A/C not cooling in hot weather...

[mdavis]

I have a 2-story home. Main (upper) floor is 2600 sq ft. and has a 4 ton American Std (installed 2005) A/C with a American Std. CUC...furnace. The air coming out of the ducts is weak to moderate in pressure and the temps are very high...over 80 now (100 out, 90 in home, 80 at the register)...best case is ~60 from the closest register when it's 70 inside...the delta T, if I understand this correctly, is usually 10. Best case 15. First company, which seems clueless, said the refrigerant level is OK, although they put 11lbs in earlier this year (they also added a drainage pan to the furnace in the garage attic and probably leaked it all out when they did the work there). There are some windows, cathedral ceilings, Marvin low-e glass, and I have not run a manual-J, but I have a hard time believing that the windows are the problem.

The bottom floor has a 2.5 ton A/C, is only 2000 sq ft. The bottom floor system is able to "keep up", meaning that I can maintain ~72 degrees when it gets hot here in Oregon...lots of 95/100 degree temps lately. The temp of the air coming out of the registers is very cool, pressure good, all is well. Right now, it's 75 in there, 100 outside, and 49 degree air is coming out of the registers...

My problem is the upper floor system...the ducts are run in the attic with cathedral ceilings...could it be a leak there, or do you think the evaporator coil is the wrong temp. or the EPR/TXV/whatever is not configured properly?

Thanks, -mark

[XFILES]

did the tach put 11 lb. of refrigerant or is that what he told you?
11 lb. for a 4 ton unit is to much that might be your problem

[bmathews]

did the tach put 11 lb. of refrigerant or is that what he told you?
11 lb. for a 4 ton unit is to much that might be your problem

Unless it was bone dry empty. In which case you have other problems.

[mdavis]

Yeah, I think they emptied the system when they moved the furnace to add a pan...it was installed in a garage and by code they didn't have to provide one...but I wanted it...Anyway, I don't think that is the problem because they came back a few months later and said it was within .25lbs of optimal...and the temps had changed a lot...so while I was concerned about a leak...it didn't seem to be the case...

Anyone know a really smart and competent tech. in Portland, OR? I want to solve this correctly...I'm convinced the tech's I've tried were clueless at this point.

[mdavis]

did the tach put 11 lb. of refrigerant or is that what he told you?
11 lb. for a 4 ton unit is to much that might be your problem

Really? Yeah, that is what I remember...11lbs...They put the gauges on the unit recently and seemed to think it needed .25 more...and that whatever it had, it was right...Maybe they are totally clueless...

I'd really like to know ASAP, since it's OVER 100 here in Portland, and my house is 90...HELP!

[2old2rock]

Delta T 10, best case 15 - Not even close. You need a competant tech.

[XFILES]

Really? Yeah, that is what I remember...11lbs...They put the gauges on the unit recently and seemed to think it needed .25 more...and that whatever it had, it was right...Maybe they are totally clueless...

I'd really like to know ASAP, since it's OVER 100 here in Portland, and my house is 90...HELP!

Did the technician took the head pressure and the low pressure?
do you know that it is?

[mdavis]

Did the technician took the head pressure and the low pressure?
do you know that it is?

They took it...No idea what it is at this point.

If you are, or know, a really good tech. in Portland, OR, and want to fix this problem, please IM.

Thanks, -mark

[mdavis]

So, I went up in the attic and;

1. The emergency drain pan in full of water...the pan UNDER the unit...it's leaking from a corner of the unit...Is the coil frozen? Does that mean it has too little refrigerant? Leak?

2. I heard a hissing sound, from what appears to be leaking air around the ducting.

Oh my...what a complete mess. This is the unit that was disconnected, moved, and re-connected to install the drain pan...and it appears the company did a terrible job...

[smittyii]

So, I went up in the attic and;

1. The emergency drain pan in full of water...the pan UNDER the unit...it's leaking from a corner of the unit...Is the coil frozen? Does that mean it has too little refrigerant? Leak?

2. I heard a hissing sound, from what appears to be leaking air around the ducting.

Oh my...what a complete mess. This is the unit that was disconnected, moved, and re-connected to install the drain pan...and it appears the company did a terrible job...
if someone has had recent work done to a system whether it was us or somebody else, that is the first place to look. you may have a float switch in your new pan. remove the water with a wet vac and call the tech back, they need to make it right. if you do have a float switch and the system comes back on after removing the water you STILL need to call them back, there IS a problem.

[mdavis]

Yeah, the company who did the work did a very bad job.

I noticed the liquid line was bent into a 270, the drain for the pan was mounted in a way that will not drain unless the pan is 99% full, all the tape is coming off the unit and the vents are no longer air-tight, etc. The unit is leaking water everywhere - and the A/C coils are on top of the unit, which is bad since the water is leaking down the side of the unit...What a mess...what an incredible mess.

They said they can come by next week, it's 100 Mon -> Wed this week and the system is completely dysfunctional.

If you live in Portland, I have a company you need to avoid.

[gasser65]

Do you still have the AC turned on? If so, go outside and look at the big copper line that goes into the outside unit - if it is iced up, you need to turn the ac off until it can thaw out. You have checked your air filter to make sure it is clean haven't you?

[mdavis]

I turned the system off at noon.

It was iced up at the coil, it was leaking water out the condensate like a hose.

I'm thinking of turning it back on soon.

[mdavis]

System was off for about 10 hours.

Turned it back on.

Return temps are 90. Air coming out of the registers is 77. Airflow is improved.

How does one get a better TD? Cool the coil lower? Since the coil just froze up, I suspect that isn't what we want to do.

[gasser65]

Quite a few things can cause the problem you are having, but it boils down to one or both of these problems: Low air flow across the indoor coil or insufficient amount of refrigerant getting to the coil. You just need to get a competent tech to check things out - do yourself and the tech a favor though - don't run the unit so long that it is frozen up when he comes or you'll be paying him to sit around and watch ice melt. Good luck!

[udarrell]

I have a 2-story home. Main (upper) floor is 2600 sq ft. and has a 4 ton American Std (installed 2005) A/C with a American Std. CUC...furnace. The air coming out of the ducts is weak to moderate in pressure and the temps are very high...over 80 now (100 out, 90 in home, 80 at the register)...best case is ~60 from the closest register when it's 70 inside...the delta T, if I understand this correctly, is usually 10. Best case 15. First company, which seems clueless, said the refrigerant level is OK, although they put 11lbs in earlier this year (they also added a drainage pan to the furnace in the garage attic and probably leaked it all out when they did the work there). There are some windows, cathedral ceilings, Marvin low-e glass, and I have not run a manual-J, but I have a hard time believing that the windows are the problem.

The bottom floor has a 2.5 ton A/C, is only 2000 sq ft. The bottom floor system is able to "keep up", meaning that I can maintain ~72 degrees when it gets hot here in Oregon...lots of 95/100 degree temps lately. The temp of the air coming out of the registers is very cool, pressure good, all is well. Right now, it's 75 in there, 100 outside, and 49 degree air is coming out of the registers...

My problem is the upper floor system...the ducts are run in the attic with cathedral ceilings...could it be a leak there, or do you think the evaporator coil is the wrong temp. or the EPR/TXV/whatever is not configured properly?
Thanks, -mark
At 100-F, you're way above the summer design in Portland, OR.
What was the Heat Index?

Summer Design in Portland, OR is 85-dry bulb & 67-wet bulb or around a low 32% relative humidity.

How high was the humidity in your home?

First, the indoor SA/RA temp/split should be 18 or 19-F at 50% relative humidity in your home, not 10 or 15-F.

So, (installed in 2005) it's probably a 12-SEER system.

First, you make sure it is not drawing hot air from the attic or garage areas.

The condenser air discharge should be about 17 or 18-F above the outdoor temperature.

That is the amount of heat transfer that should be taking place.

Get a $10 humidity gauge for indoors at a local hardware store.
At 50% RH, the the supply air with a proper airflow CFM should be 18 to 20-F.

Make sure the airflow is at-least 400-cfm per ton of cooling, or for 4-ton 1600-cfm.

Get the entire duct system sealed with duct mastic.

"Take a thermometer & check the air temperature coming off the outdoor condenser."

Locate the small uninsulated copper line where it makes a bend, outdoors or indoors, so you can put a digital thermometer flat on it & insulate theTH with something (piece of the tubing insulation) read the temperature & subtract it from the outdoor condenser discharge air temp.

E.g., condenser temp 110, line temp 100-F that is 10-F subcooling & 10 to 12-F is a normally charge system. If it's considerably less than 10-F it could be low on refrigerant or need a Tech to check it; too far above 12-F it's overcharged, call a Tech, could also be a restriction in the lines.

You should own a low cost digital pocket thermometer; anyone can Ballpark check the charge with a little low cost MA-Line digital thermometer & using some tubing insulation on the sensor probe. Inquire at hardware stores, etc.
http://www.ma-line.com/HTML/L1_productmenu.html

Take the outdoor temperature & subtract it from the outdoor condenser's discharge air temperature. Should be 17 to 18-F.

These outdoor condenser temperatures are standard for different SEER Rated units.
A 12-SEER unit, with 50% relative humidity indoors will have ballpark, 18 to 20-F condenser temp/split

A 14-SEER will be around a 14 to 16-F condenser temp/split. if too far above or below those temps, call for an A/C Tech. - Darrell

[mdavis]

Thanks for the detailed Responses!

Here is where we are.

The refrigerant was about .5lbs low again...we suspect a faint leak...All the contractor did was tighten a liquid line fitting at the A coil. I have an "imposter 2" by bacharach and it was not happy with a 270 degree turn on the liquid line in front of the furnace/coil connection.

Using a Fluke 561 (got one last night just for this), the temps in/out on the condensor were about 20 delta-T after they refilled the refrigerant.

Inside, we see 15 for a TD, ranging from 14-17....measuring the temp coming out of the register and the avg. room temp at a return....right now: 66 vs. 81 in the home.

We did find a few small leaks in the attic supply lines, but I would be surprised if they were enough to matter.

Home humidity varies from 35-55...today it's 38, but it's going to be 104 outside.

I don't know the SEER of the A/C system, it's Ameristar, built 8/2004. 2A7B0048A1000AA...Anyone know anything about this one?

The furnace is an American Std...the furnace is a single speed 4 ton unit CUC100A...with 90 eff.

So, we're going to wait for it to leak again, and then they might evac. the system and try to find the leak.

I measured ranges of 101-104 on the condensor output and 91-94 on the liquid line.
-mark

[udarrell]

Thanks for the detailed Responses!
Here is where we are.

The refrigerant was about .5lbs low again...we suspect a faint leak...All the contractor did was tighten a liquid line fitting at the A coil. I have an "imposter 2" by bacharach and it was not happy with a 270 degree turn on the liquid line in front of the furnace/coil connection.

Using a Fluke 561 (got one last night just for this), the temps in/out on the condensor were about 20 delta-T after they refilled the refrigerant.

Inside, we see 15 for a TD, ranging from 14-17....measuring the temp coming out of the register and the avg. room temp at a return....right now: 66 vs. 81 in the home.
It's probably a 10 or 12-SEER with 2004 date (?).
With a low 38% relative humidity, unless the airflow is terribly high the temp/split would usually be considerably higher than 15-F.

The airflow temps & velocities shoud be relatively uniform from room to room.
What size ductwork is there?

The Return air is extremely important, & two large exterior filter racks may be called for.

Most 4 & 5-Ton systems require two filter racks exterior of the airhandler to achieve a low enough air velocity through those filters.

Most 4 & 5-Ton systems nearly always have too much air velocity through initial clean filters, let alone when they begin loading.

Divide the rated CFM the duct is carrying by the free area sq.ft. of the Return Air grille for airflow velocity in FPM without a filter in the rack.

Figure 2-cfm per one sq.in. of figured free-air-area: 1600-CFM/800-sq.ins. = 2 X's 144= 288-FPM velocity, but add the filter, & it loads.
Checking formula: 800-sq.ins / 144-sq.ins.= 5.555555-sf X's * 288-fpm = 1600-CFM.
If possible, keep airflow through filters within 350-cfm.

The filter will reduce the sq.ft. free-air-area, thus increasing the fpm velocity, as it loads.

*All filter mfg'ers should print the free air area of the clean filter on the edge of the filter (we need that data) along with the pressure drop data.

Divide the rated CFM the duct is carrying by the free area sq.ft. of the filter for airflow velocity in FPM. (Or use above formula with the duct's sq.ft. area for duct airflow velocity)


We did find a few small leaks in the attic supply lines, but I would be surprised if they were enough to matter.

Home humidity varies from 35-55...today it's 38, but it's going to be 104 outside.

I don't know the SEER of the A/C system, it's Ameristar, built 8/2004. 2A7B0048A1000AA...Anyone know anything about this one? (10 or 12-SEER)

The furnace is an American Std...the furnace is a single speed 4 ton unit CUC100A...with 90 eff.

So, we're going to wait for it to leak again, and then they might evac. the system and try to find the leak.

I measured ranges of 101-104 on the condensor output and 91-94 on the liquid line. (Ten Subcooling, should be okay unless mfg'er calls for more.)
-mark

[mdavis]

UPDATE: system is again at a TD=0. Likely have a small leak and a frozen coil again. Portland, OR recommendations?

Udarrell- there are two return air vents...probably 14x14 or so each. Moved the filters down from 13 MERV to 10.

[crmont]

mdavis.. From what I've read you may have a low airflow issue and your system may not have a TXV at the evaporator coil. If your system really holds 11lbs and a leak is the problem, then you have a rather large leak.

As a tech in Oregon, I've found many poorly designed duct systems causing freezing issues at the evaporator. Your Furnace has a maxed out 4 ton blower with what is likely a PSC motor. This type of system must have a properly designed duct system for a PSC motor to achieve the 1600 cfm necessary. I've seen 4 ton systems only produce 800 cfm simply because of an insufficient duct system and undersized filters. Do I understand that you have 2 14x14 filters? If so, that's undersized for a 4 ton system.

Systems that are poorly installed are prone to freezing in Oregon because the ambient temps can dip into the low 50's at night even when it's been 100 deg the previous day. The owner will turn the stat so low that it won't shut off all night and if you have poor airflow and the lack of a TXV, any system will freeze.

If you wan't to find the exact performance of your system, check with your local utility company and inquire about a "CHECK ME" service. This type of service will document your airflow and charge level. Make sure the tech uses the flow plate method to check the cfm WHILE the filters are installed.

[mdavis]

Systems are American Standard CUCs. No idea on the motors used...the coil was a cheap A-coil.

The 4 ton has 2 return ducts that are roughly 14x14 or 16x16. There is a Honeywell 5" 20x25 filter FC100A1037 on the unit. I moved it from MERV 13 to 10 to increase airflow and lower pressure drop.

I was told there was no TXV. Correct. Is that an issue in Oregon? My other system doesnt have one and it works great.

I doubt I have 1600cfm, but I have no measured.

-mark

[crmont]

The lack of a txv on larger (3-5 ton) high efficiency (12+ seer) equipment can be an issue in low ambient conditions, especially with a lack of evaporator air flow. Did the system freeze over night or during the day?

Thats a good filter btw.

A txv will compensate for low ambient conditions, long lines and also make it easier to charge.

What is the vertical rise and over all lineset length?

Has this system ever worked right?

Barring any other issue, If the coil freezes generally with a freezing suction line, then it's low air flow. If it freezes gradually, begining from the distributor tubes, then it's low on charge or not enough refrigerant passing the metering device. Don't leave any doors off the system for more than 1 min.

[udarrell]

Systems are American Standard CUCs. No idea on the motors used...the coil was a cheap A-coil.

The 4 ton has 2 return ducts that are roughly 14x14 or 16x16. There is a Honeywell 5" 20x25 filter FC100A1037 on the unit. I moved it from MERV 13 to 10 to increase airflow and lower pressure drop.

I was told there was no TXV. Correct. Is that an issue in Oregon? My other system doesnt have one and it works great.

I doubt I have 1600cfm, but I have no measured.
-mark
A single 25X20 is 500sq.ins (filter's free air area? a guess say 75%, or 375-sq.ins. or 2.6-sq.ft / into 1750-cfm is 673-fpm velocity-fpm velocity through the filter. It should have close to half that through clean filter(s).

Therefore, all the filtering should be accomplished through larger filter grilles at the entry of each RA duct-run. Using 2000 / 2= 1000-sq.ins of filter grille area. The grille reduces the area by 25% or 1000 * .75 = 750-sq.ins of free air area. Therefore, 1250-sq.ins. provides 1000 but without the filter restrictions!
Therefore, 1250=1000-sq.ins free-air-area (equivalent to two 25X25 or combinations = near 625-sq.ins. filter grilles = 6.94-sq.ft., / into 2000-cfm= 288-fpm w/o the filter restrictions which will increase considerably the velocity. :) - Darrell

[crmont]

A single 25X20 is 500sq.ins (filter's free air area? a guess say 75%, or 375-sq.ins. or 2.6-sq.ft / into 1750-cfm is 673-fpm velocity-fpm velocity through the filter. It should have close to half that through clean filter(s).

Therefore, all the filtering should be accomplished through larger filter grilles at the entry of each RA duct-run. Using 2000 / 2= 1000-sq.ins of filter grille area. The grille reduces the area by 25% or 1000 * .75 = 750-sq.ins of free air area. Therefore, 1250-sq.ins. provides 1000 but without the filter restrictions!
Therefore, 1250=1000-sq.ins free-air-area (equivalent to two 25X25 or combinations = near 625-sq.ins. filter grilles = 6.94-sq.ft., / into 2000-cfm= 288-fpm w/o the filter restrictions which will increase considerably the velocity. :) - Darrell


In a practical application, his filter system is about the best that you will see installed out here. (I like merv 8 honestly.) Maximum air flow capacity for a merv 11 of his size (20x25x5 1/4) is around 2000 cfm so I'm not so concerned about his filter situation yet.

[udarrell]

I agree, that is what you will see, I was merely illustrating optimal Return-Air & filtering conditions.

If the static (ESP) needed lowering, something on the order of what I showed would drop it considerably for more efficient blower performance as well as filtering. - Darrell

[mdavis]

The lack of a txv on larger (3-5 ton) high efficiency (12+ seer) equipment can be an issue in low ambient conditions, especially with a lack of evaporator air flow. Did the system freeze over night or during the day?

Thats a good filter btw.

A txv will compensate for low ambient conditions, long lines and also make it easier to charge.

What is the vertical rise and over all lineset length?

Has this system ever worked right?

Barring any other issue, If the coil freezes generally with a freezing suction line, then it's low air flow. If it freezes gradually, begining from the distributor tubes, then it's low on charge or not enough refrigerant passing the metering device. Don't leave any doors off the system for more than 1 min.

I have not been able to confirm it is frozen -- I didn't see a ton of drainage from the condensate line and it continues to have a TD of about 2-3 degrees this morning...after I had it off all night.

The lineset is very long, probably 120'.
The vertical rise is also very significant, estimate about 30'. !!! I probably should have noted that.
I don't have a 90 count...i

I'm a new owner, so I don't know if the A/C ever worked correctly..not for me...every time it is recharged, it is fine for a few weeks...fine as defined by TD = 15/16...not really optimal.

[smittyii]

I have not been able to confirm it is frozen -- I didn't see a ton of drainage from the condensate line and it continues to have a TD of about 2-3 degrees this morning...after I had it off all night.

The lineset is very long, probably 120'.
The vertical rise is also very significant, estimate about 30'. !!! I probably should have noted that.
I don't have a 90 count...i

I'm a new owner, so I don't know if the A/C ever worked correctly..not for me...every time it is recharged, it is fine for a few weeks...fine as defined by TD = 15/16...not really optimal.
120 ft lineset could be a game changer. low speed compressor is probably struggling, i would definitley check that out.

[mdavis]

120 ft lineset could be a game changer. low speed compressor is probably struggling, i would definitley check that out.

Can you please elaborate? Is it possible I need a higher speed compressor?

[udarrell]

I have not been able to confirm it is frozen -- I didn't see a ton of drainage from the condensate line and it continues to have a TD of about 2-3 degrees this morning...after I had it off all night.

The lineset is very long, probably 120'.
The vertical rise is also very significant, estimate about 30'. !!! I probably should have noted that.
I don't have a 90 count...i

I'm a new owner, so I don't know if the A/C ever worked correctly..not for me...every time it is recharged, it is fine for a few weeks...fine as defined by TD = 15/16...not really optimal.

Actually, we have to use piping equivalent lengths; 90-ells, dryers, etc., have a small added footage length that is added to the measured length.

A 4-Ton with those piping lengths using 7/8th suction line, could be losing over 9%; I factored in other things to get a 12% loss of cooling capacity.

A 12% loss drops a 4-ton capacity to 3.5-ton.

Should probably go to 1-1/8th inch OD suction line to reduce to 1 or 2% capacity loss.

The liquid line would probably have to be up-sized too. - Darrell

[smittyii]

Actually, we have to use piping equivalent lengths; 90-ells, dryers, etc., have a small added footage length that is added to the measured length.

A 4-Ton with those piping lengths using 7/8th suction line, could be losing over 9%; I factored in other things to get a 12% loss of cooling capacity.

A 12% loss drops a 4-ton capacity to 3.5-ton.

Should probably go to 1-1/8th inch OD suction line to reduce to 1 or 2% capacity loss.

The liquid line would probably have to be up-sized too. - Darrell
plus you factor in that the smaller compressor is not full tonnage.

[crmont]

Fix the leak, add a txv and a low ambient kit. This should fix the long line and freezing issues.

[mdavis]

Interesting development. TD went to 0.

Had the tech. out, no R22 left.

Turns out there is a lot of oil leaking from one of the coils in the condensor.

Recommendation was to replace the coil at the 4 ton Ameristar condensor unit. Price was ridiculous, and the part is apparently under the 5 year warranty and free.

Guy wanted to add a filter to the liquid line as well, recommended??

He said he only brings the system to 500mils, reasonable? My wine cellar was down around 150 on refill.

There is no trap in the 30 ft. drop liquid line, should I have one added?? There were some SLIGHT curves in the line, but very slight.

The guy was trying to up-sell me on a lot of things...wanted to move the liquid line from 7/8" to 1 1/8"...wanted to sell me a new furnace because the airflow is low and it's a single-speed CUC American Std -- can't I just replace the blower motor?

Also pointed out a leaking cap. at the blower -- oil was dripping out of it, worries??


So, I have to believe the leak was in the compressor coil all along, but just in case, the line is at 250psi outside the coil...just to check the rest of it.

Is it still OK to leave the furnace in heat mode?

Thanks, -mark

[crmont]

Interesting development. TD went to 0.

Had the tech. out, no R22 left.

Turns out there is a lot of oil leaking from one of the coils in the condensor.

Recommendation was to replace the coil at the 4 ton Ameristar condensor unit. Price was ridiculous, and the part is apparently under the 5 year warranty and free.

Guy wanted to add a filter to the liquid line as well, recommended??

He said he only brings the system to 500mils, reasonable? My wine cellar was down around 150 on refill.

There is no trap in the 30 ft. drop liquid line, should I have one added?? There were some SLIGHT curves in the line, but very slight.

The guy was trying to up-sell me on a lot of things...wanted to move the liquid line from 7/8" to 1 1/8"...wanted to sell me a new furnace because the airflow is low and it's a single-speed CUC American Std -- can't I just replace the blower motor?

Also pointed out a leaking cap. at the blower -- oil was dripping out of it, worries??


So, I have to believe the leak was in the compressor coil all along, but just in case, the line is at 250psi outside the coil...just to check the rest of it.

Is it still OK to leave the furnace in heat mode?

Thanks, -mark

Sounds like he knows what he's doing. We told you most of those things already. BTW it's the suction line to be enlarged not the liquid line. He's not "up-selling", he's trying to protect your investment by installing things the right way.

[mdavis]

So, options at this point are:

1. fix coil. the price is surprisingly high.
2. replace unit with a new carrier 4ton. are the coils compatible? could get cash back and a tax credit that may pay for a new high eff.
3. trane? 20seer.

I will ask them to install oil traps and perhaps a filter as well in the line.

Still torn on whether I need to move up to 1 1/8".

Do I have to replace the evaporator coil if I want to buy a 21SEER? Current is around 10-12. I think the coil is an ADP A-coil.

Who makes the best condensor units these days? I have a commercial control system that is web-based, so I want to continue to use that (not infinity, so don't know if the humiditty control helps...my system will run the A/C to control humidity)...Recall my furnace is a American Std CUC 4ton and my broken condensor is a 4 year old Ameristar.

Thanks, -mark

[crmont]

So, options at this point are:

1. fix coil. the price is surprisingly high.
2. replace unit with a new carrier 4ton. are the coils compatible? could get cash back and a tax credit that may pay for a new high eff.
3. trane? 20seer.

I will ask them to install oil traps and perhaps a filter as well in the line.

Still torn on whether I need to move up to 1 1/8".

Do I have to replace the evaporator coil if I want to buy a 21SEER? Current is around 10-12. I think the coil is an ADP A-coil.

Who makes the best condensor units these days? I have a commercial control system that is web-based, so I want to continue to use that (not infinity, so don't know if the humiditty control helps...my system will run the A/C to control humidity)...Recall my furnace is a American Std CUC 4ton and my broken condensor is a 4 year old Ameristar.

Thanks, -mark


To get any type of tax credit or otherwise, your system (condenser, coil, air handler) must have an ARI match. R410 refrigerant and POE oil is more miscible than r-22 so i believe whistle1 will handle long linesets better than r-22. All of the particulars; lineset sizing, oil traps, filter driers ect, are plainly described in the installation instructions. Most of those instructions are online somewhere so get the model numbers and research your choices. This is what the contractor should be doing as well.

[mdavis]

So, in order to qualify for the credit, I will probably have to replace the furnace? Current American Std. is a single-speed CUC..

I am now researching Carrier vs. Trane. I wonder if I should just put a high eff. condensor out there? Perhaps a new coil as well.

May get some S/W for a manual J today to see if 4 tons is sized properly...the ystem wasn't keeping up...2700 sq ft. on the top level with tons of Southern windows and cathedral ceiling and 3 large skylights...was 4 tons, may consider 5...

-mark

[udarrell]

So, in order to qualify for the credit, I will probably have to replace the furnace? Current American Std. is a single-speed CUC..

I am now researching Carrier vs. Trane. I wonder if I should just put a high eff. condensor out there? Perhaps a new coil as well.

May get some S/W for a manual J today to see if 4 tons is sized properly...the ystem wasn't keeping up...2700 sq ft. on the top level with tons of Southern windows and cathedral ceiling and 3 large skylights...was 4 tons, may consider 5... -mark
With cathedral ceilings, leave the hot air up there, let it stratify.
That warm air acts as an insulating blanket as there is far less temp difference for temp migration.

I am reminded of stratfication every time I go up the stairwell to the 2nd floor & hit the hot humid air that the 1st floor room A/C didn't affect.

Never cool & condition the areas that don't need it!

Engineer everything in an attempt to only cool the air at or near up to an eight foot height.

Is there anyway you can get them to stop the solar-gain from those 3 large skylights?

If everything is figured just right for cooling, you may get by with the same or less cooling tonnage. (?) - Darrell

[crmont]

So, in order to qualify for the credit, I will probably have to replace the furnace? Current American Std. is a single-speed CUC..

I am now researching Carrier vs. Trane. I wonder if I should just put a high eff. condensor out there? Perhaps a new coil as well.

May get some S/W for a manual J today to see if 4 tons is sized properly...the ystem wasn't keeping up...2700 sq ft. on the top level with tons of Southern windows and cathedral ceiling and 3 large skylights...was 4 tons, may consider 5...

-mark

Historically, some condenser/evaporator combinations have had high enough efficiencies to qualify for the credits without replacing the air handler but many more (and cheaper) systems qualify when the air handler is also replaced.

Not keeping up under what circumstances?

[crmont]

With cathedral ceilings, leave the hot air up there, let it stratify.
That warm air acts as an insulating blanket as there is far less temp difference for temp migration.

I am reminded of stratfication every time I go up the stairwell to the 2nd floor & hit the hot humid air that the 1st floor room A/C didn't affect.

Never cool & condition the areas that don't need it!

Engineer everything in an attempt to only cool the air at or near up to an eight foot height.

Is there anyway you can get them to stop the solar-gain from those 3 large skylights?

If everything is figured just right for cooling, you may get by with the same or less cooling tonnage. (?) - Darrell

What about humidity?

[udarrell]

What about humidity?

Well, we're talking about grains of moisture per lb of air.
Warmer air holds more grains of moisture at a specific %RH.

Water vapor migrates from areas of higher absolute humidity to areas of lower.
http://forum.onlineconversion.com/showthread.php?t=567

Maybe the separation is greater, - but the humidity level was higher & muggier as I walked up in to the unconditioned upstairs air.

It appears it would depend on the ratio of which air temp could absorb the most grains of moisture from the other.

I thought the humidity would migrate to the downstairs, but for the most part, it didn't seem to do that.

I am NOT the world's expert on that topical question!

Perhaps we have someone that could deal with it with more clarity. - Darrell

[mdavis]

Thanks for all the help everyone.

I started a new thread for sizing the system:

http://hvac-talk.com/vbb/showthread.php?t=364672

Anyone have the sensible stats for the top few Carrier and Trane A/C units in 5 tons? (assuming I did the calcs right).

The options are:

1. replace the 4 ton Ameristar coil - maintain the crappy Ameristar and 4 tons
2. replace the 4 ton Ameristar with a 5 ton Trane or Carrier...without a furnace replacement, doubt I will qualify for any tax credits in 5 ton? Perhaps if I went the heat pump route, rather than just getting a new A/C?
3. replace the 4 ton Ameristar with a 5 ton Trane or Carrier with XC95 or carrier equiv. furnace. The adv. would be better humidity control and a more efficient furnace and a tax rebate, but the cost is probably too steep for now.

-mark

[mdavis]

Historically, some condenser/evaporator combinations have had high enough efficiencies to qualify for the credits without replacing the air handler but many more (and cheaper) systems qualify when the air handler is also replaced.

Not keeping up under what circumstances?

Here in Portland, OR, we've had some interesting weather...weeks of 100ish highs...weeks of 90ish highs...

In those cases, the setpoint was 74 and my home was quickly at 80/82 on the top floor (the system that is broken)...the bottom floor system kept up for the most part.

Oh boy...Anyone know the model #s of some Trane and Carrier higheff A/Cs I could try?

I see:
24ANA1 and 24ANA7 for Infinity and 24APA5 for the Perf. 15 from Carrier...but I don't have the specific model #s for the 5 ton units.

Same for Trane...XL20i,XL19i,XL15i...with 5 tons?

No idea on the matching evaporator coils.

If I had all that, I'd attempt to use http://www.ahridirectory.org/ahriDirectory/pages/ac/defaultSearch.aspx

Or, perhaps, someone who knows what the hell they are doing can put together a few systems that would work??

Would you recommend going heat pump or sticking with the A/C?

-mark

-mark