A-coil totally iced up...UPDATE w/pics

[VincentR]

In a continuation form this post...
A-coil iced up, (http://www.hvac-talk.com/vbb/showthread.php?t=140910)
I decided to see how dirty the inside of the coil was. I removed the ductwork from around it and was really hoping to see a clog in there. Couldn't imagine how it would be so dirty though as I have a Space-Guard high efficiency filter on the inlet of the blower. But anyway. The pics below are what I saw. Looks pretty clean to me. Do you guys see anything here that could be my problem? I used a fine brush and a vacuum and cleaned it the best I could, but really didn't remove any dirt/buildup. Is the rust/corrosion on the outside frame of the A-coil anything to be concerned with? Unit is 11 years old.
Thanks in advance for your time/feedback.

http://www.chevelles.com/showroom/data/500/medium/100_1629.JPG

http://www.chevelles.com/showroom/data/500/medium/100_1630.JPG

http://www.chevelles.com/showroom/data/500/medium/100_1631.JPG

http://www.chevelles.com/showroom/data/500/medium/100_1632.JPG

http://www.chevelles.com/showroom/data/500/medium/100_1633.JPG

[acmech13]

call a tech. you need service.

[Jabarco]

What is your External Static Pressure measured at the furnace? BTW, you'll need to run the cooling for about 15 minutes first and then measure the ESP with the cooling on. Why? Because you should have a wet coil before measuring the your ESP because there is a difference in measured ESP between a wet and dry evaporator coil.

Hey, I can't help it if you don't have a magnehelic gauge!

[Senior Tech]

Noone here can "see" the problem without being there, in person, with the proper equipment to analyze and diagnose your problem. Do yourself a favor, call a reputable company to do the above.

[Gunnery Sergeant Hartman]

wow, you did alot of work taking that apart for nothing...

This is not a problem that a DIY can diagnose.

[AIR PRO]

I see the leak(s). :p

[Shophound]

Oh well...it LOOKED like dirt through the ice. I've seen it before, but a photo is never as good as being there. Shows why this internet diagnosis gig ain't gonna be dead on...

[ga-hvac-tech]

Just my personal opinion: You probably have a more serious problem, one that is not easily diagnosed (the old 'arm chair' method will not work this time).

You really need a quality tech out there. What part of the country are you in?

[VincentR]

wow, you did alot of work taking that apart for nothing...



Not really, I confirmed the coil was clean. I wouldn't say that was a lot of work for nothing. It wasn't what I would call hard work getting to it. It's all back together now and the fan is running. I'll call a local HVAC guy tomorrow.
...I do have a magnahelic and a photohelic at work. I can bring it home and measure for my own reference for future tests.

I am in Northeat PA, Nazareth PA, about 15 minutes NE of Allentown.
Thanks for the input guys, I do appreciate it.

[acmech13]

you working with sheet metal or ductboard?

[VincentR]

you working with sheet metal or ductboard?

Sheetmetal, why do you ask?

[Jabarco]

...I do have a magnahelic and a photohelic at work. I can bring it home and measure for my own reference for future tests.


If you call a service guy out, be sure to ask him what the external static pressure is. A ½ inch of water column would be ideal but not likely.

Jabs

[ga-hvac-tech]

Who wants to bet that system is choked (as in cannot get enough air to flow)???

That spacegaurd is a GREAT air filter, but there needs to be enough physical area on both sides of it (read that ductwork) to flow enough air to allow the system to breathe.

Be SURE you get the tech that comes out to check external static pressure (both on supply and return).

While you are at it, get the tech to check SH and SC (superheat and subcooling), with the air temps at the time checked (outdoor and indoor dry bulb, and indoor wet bulb).

And let us know what you (and the tech) find...

[VincentR]

I called the service guy this morning. They are busy around here now, so I have to wait a few days. I understand your point about the system being choked/starved for air, but this is not a new install. House/system is 11 years old. This is the first time it has iced up. Unless of course the blower motor is dying in my furnace, but it feels like normal airflow through all of the A/C registers throughout the house. I will let you know what he finds.

[ga-hvac-tech]

You would be amazed if you rode with at tech that understood airflow (many do not), and saw that literally most residential installations are grossly under-ducted (yeah, I just created a hyphened word).

At least 3 out of 4 change-outs I do need duct modification to let it 'breathe' freely. All I can figure out is that the builder does not care cause he does not live there, and cheaper means more profits...

Please do let us know what you find, and BTW: The idea that a blower motor is going out does hold credence. They tend to run a little slow w/out it being easily noticeable, and they tend to stop/start (heat overload) the last few days/weeks before they will not start.

Also could be low in refrigerant, but a tech will have to verify that one.

Is it working well enough for you to keep the house comfortable until they get out there? Hope so.

[VincentR]

Yep it is workin sort of OK now that I thawed it out.:) I also bumped the temp up to 76 degrees from 73 degrees. I took some pressure measurments this evening. Somebody at work had my 0-1 "H20 magnahelic gauge, so I had to do it with a 0-5" gauge. Not nearly as accurate, but good enough until tomorrow. I got;

Fan running only, with filter in place;
Return plenum before filter (point A) = -.20
Return plenum at blower inlet (point B) = -.60
After blower, before A-coil (point C) = +.50
After A-coil (point D) = +.20

Fan running only, no filter in place, but filter housing sealed.
A = -.30
B = -.50
C = +.50
D = +.25

A/C unit running with filter in place "wet" >30 minutes, House at 77, T-stat set to 73
A = -.20
B = -.60
C = +.55
D = +.20

3 hours later, house at 73 degrees,
A = -.20
B = -.60
C = +.60
D = +.15 Bottom 1/2 of A-coil had frost on it. So I set the t-stat back up to 76 degrees and set the fan to run continuous. Gotta wait for the tech to arrive. Also going to repeat my test tomorrow with my 0-1" Dwyer magnahelic.

[AIR PRO]

I got $20 say's it a leak in the evap coil, any takers? :D

[Advanced Response]

If your measurements are at all accurate... Your duct work is undersized on the return as well as the supply... You have a total external static pressure of 1.15 inches which is well outside of the design static of .5 for proper airflow..

However your pressure drop across the spacegard and the evaporator are inline..

I also suspect a refrigerant leak.. that could be in the evaporator or anywhere in the refrigerant circuit..

Goodluck
J

[BigJon3475]

His run cap just went out not to long ago on the evap fan. It was bulged out. I'm thinking fan issues if it's 11 years old.

[ga-hvac-tech]

Hi Vincent,

THX for taking the time to do all the measurements, although I suspect it is fun for you... :)! You have already confirmed what some of us thought, that being the ductwork in the house is a bit small (not unusual, actually it would be unusual if it were properly sized--seriously).

Now I read that Air Pro says you have a refrigerant leak, and BigJohn says you thinks you may have a weak blower motor (moves the air through the furnace).

I will put my money on all three (yes, it took more than one problem to force the system into this mess). However, think of it this way: If all the problems were corrected properly, your energy bills would go down, and your home would be lots more comfortable than you are accustomed to. And after all, what is the system there for... but comfort!!!!!!!!!

Please do keep us posted as to what the tech finds, it will be interesting to hear!

[VincentR]

GA-HVAC,....just to be sure we are on the same page....the cap I replaced a few weeks ago was for the fan on the outside unit (condesner fan). It was one of those dual run caps 5/40 uF. One for the fan and one for the compressor. When I replaced that cap, I also cleaned the coils outside. Although they were pretty clean to begin with. I also tested the speed of that motor and it is spinning at spec (850RPM). I have not tested the fan speed of the blower motor in my furnace yet though. I'll stick that on my list of stuff to do. As a homeowner waiting for my tech, I dont mind doing this stuff, I do have access to various pieces of test equipment and I learn a lot along the way.

[BigJon3475]

GA-HVAC,....just to be sure we are on the same page....the cap I replaced a few weeks ago was for the fan on the outside unit (condesner fan). It was one of those dual run caps 5/40 uF. One for the fan and one for the compressor. When I replaced that cap, I also cleaned the coils outside. Although they were pretty clean to begin with. I also tested the speed of that motor and it is spinning at spec (850RPM). I have not tested the fan speed of the blower motor in my furnace yet though. I'll stick that on my list of stuff to do. As a homeowner waiting for my tech, I dont mind doing this stuff, I do have access to various pieces of test equipment and I learn a lot along the way.


Oh my fault I mis represented. i thought in the other thread you said evap fan.

[VincentR]

Oh my fault I mis represented. i thought in the other thread you said evap fan.

No, that was my mistake. Sorry, I did say evap fan in the other post. It was the condenser fan that stopped running before. The cap was bad for that and I replaced it.

[VincentR]

I brought home a more accurate 0-1" Dwyer gauge. With the system dry, filter installed and only the blower running;
A = -.25
B = -.65
C = +.55
D = +.18

So I have a .40 drop across the filter and a .37 drop across the A-coil. Do these sound excessive?
Tech is coming to the house on Friday.

[ga-hvac-tech]

I brought home a more accurate 0-1" Dwyer gauge. With the system dry, filter installed and only the blower running;
A = -.25
B = -.65
C = +.55
D = +.18

So I have a .40 drop across the filter and a .37 drop across the A-coil. Do these sound excessive?
Tech is coming to the house on Friday.

Well, it is more than would be optimal, but .77 ESP is not too far out of line as far as what I see almost daily. Better would be .5 to .6 max, but that would probably require some ductwork modifications.

Tell us about the size of the return ductwork: What size duct, what material, and what grill(s). And what size is the A/C; is it 2 ton, 2.5 ton, etc?

[dash]

Coil could have been surfaced cleaned ,but is still impacted in the center.


Is the blower wheel dirty??

[BigJon3475]

A wet coil will be a little more restrictive also then just a fan test.

[Jabarco]

I brought home a more accurate 0-1" Dwyer gauge. With the system dry, filter installed and only the blower running;
A = -.25
B = -.65
C = +.55
D = +.18

So I have a .40 drop across the filter and a .37 drop across the A-coil. Do these sound excessive?
Tech is coming to the house on Friday.



I'm sorry but what you have given us is TSP (Total Static Pressure) and (measured by using one pitot tube). What we need to know is ESP (External Static Pressure) and (measured by using two pitot tubes).

http://i199.photobucket.com/albums/aa214/jabarco/staticpressuretip.jpg

Hey I can't help it if you don't have two pitot tubes!

[VincentR]

Blower wheel (squirrel cage) is clean.
I believe the unit is a 4-ton.
Ductwork...
Each room of the house has it's own supplies and returns. Some 1 of each, some multiple for larger rooms. Supplies are floor mounted registers with openings that measure 18" x 3" The house has a total of 18 of those. (2 story colonial, open foyer, 3000 sq-ft. Returns are mounted in the walls, some in floors and are rectangulars grates with the openings measuring 5.5" x 11". The house has 15 of these.
Return ductwork in the basement is sheetmetal, 8" x 20", then it goes to 8" x 28" where it feeds into my Space Gard filter. Supply duct is also sheetmetal. Above the furbace is the 21" x 21" enclosure where the A-coil is. Then it feeds into a 8" x 24' supply duct running across the basement ceiling. Goes about 10 feet then reduces down to 8" x 18", runs another 35 feet or so and then goes down to 8" x 14".
Not sure what you meant about measuring my pressure with one tube vs 2. My dwyer does have 2 inputs, 1 for + pressure and 1 for - pressure. I put one tube in each and came up with the deltas. Which is also the same as just subtracting one from the other. Is that not right?? Thanks for being so patient with me. I have no expertise in this field (obviously). Just trying to be an educated homeowner. I'll gladly pay the tech to troubleshoot and fix this issue. I just don't want to be clueless about the whole process.

[ga-hvac-tech]

Return seems a little restrictive to me. It was common in years past to size the return smaller than the supply, but now it understood that both need to move the same amount of air.

Is there a place in your home where a 'common' return could be placed in the floor that would not be disruptive to your lifestyle (say one or maybe two more of those existing 5.5x11 returns)? And duct them directly to that larger duct just before the spacegaurd. That will allow the system to 'breathe' a lot better.

Beyond that, I think you are probably low on refrigerant. Lets see what the tech says Friday. Be sure to get the tech to do a SH and SC readings and post them here.

THX for all the data! It is not easy to 'internet diagnose' things, but your ability to gather data has been stellar!!!

You might want to do that 'wet coil' test and post the results; do it from before the air filter to after the coil, all in one test. After all, that is the TOTAL esp over the system, and that is the number we are working with.

Have a GREAT one!

[Jabarco]

Not sure what you meant about measuring my pressure with one tube vs 2. My dwyer does have 2 inputs, 1 for + pressure and 1 for - pressure. I put one tube in each and came up with the deltas. Which is also the same as just subtracting one from the other. Is that not right?? Thanks for being so patient with me. I have no expertise in this field (obviously). Just trying to be an educated homeowner. I'll gladly pay the tech to troubleshoot and fix this issue. I just don't want to be clueless about the whole process.

Hey, don't worry about it. I'm sure that I'm not the only professionally trained air conditioning technician reading your posts. In addition, I'm certain that you having a Magnahelic gauge is more than I can say for more than half of all HVAC service technicians. Furthermore, many don't even understand ESP, or what it can tell him.

Anyways, you did an excellent job ("I put one tube in each and came up with the deltas. Which is also the same as just subtracting one from the other") of giving us the TSP. However it's not the same as ESP.

ESP can be measure by using two pitot tubes on your Magnahelic gauge and inserting the one tube in the return of the furnace and one tube in the supply of the furnace. That reading will be your ESP.

Furnace manufacturers already know how many CFM are moving through their furnaces just by knowing the ESP. Ideally, it's ½" of water column. They will be able to tell you the CFM at just about any given ESP.

[catmanacman]

iwould think that if the unit is a older unit from the rust on the coil and if the unit was working properly i would check freon level fiist btw i have never found a dirty coil in a system that had a spaceguard and also seen plenty of 2200 on 5 ton systems no problem

[VincentR]

ESP can be measure by using two pitot tubes on your Magnahelic gauge and inserting the one tube in the return of the furnace and one tube in the supply of the furnace. That reading will be your ESP.


Pardon the noobie ignorance.....
One tube in the return....Would that be before or after the filter?

One tube in the supply....Would that be before or after the A-coil?

[catmanacman]

if it is a traneyou might as well tell the service tech to bring a evap coil

[BigJon3475]

Think of it like everything you want to take readings of have to be included in the before and after. If you want filter included go before and after. If you want coil included with filter go before filter and after coil.

[Shophound]

Pardon the noobie ignorance.....
One tube in the return....Would that be before or after the filter?

One tube in the supply....Would that be before or after the A-coil?

You might find this article handy:

http://www.bacharach-training.com/Tips/esp.htm

Not sure about Jabarco's angle, but both the article and my own ESP measuring techniques involve using one static tip (or the static port on a pitot tube) to measure both locations. Thing to remember when using the Mag is to switch the hose from one port to the other when going from supply to return. As the article says, once you obtain both readings you add them together, ignoring the negative sign. That will be your ESP.

[Shophound]

Here is another excellent article from our very own Penton Media, owner of this site:

http://www.contractingbusiness.com/editorial/serviceclinic/static.cfm

[VincentR]

Good articles/tech info! Thanks.:)

[bsharp]

I brought home a more accurate 0-1" Dwyer gauge. With the system dry, filter installed and only the blower running;
A = -.25
B = -.65
C = +.55
D = +.18

So I have a .40 drop across the filter and a .37 drop across the A-coil. Do these sound excessive?
Tech is coming to the house on Friday.

Since this is a furnace with an A coil and external filter, just drop the signs before measurments B and C and add them together. You have 1.2" ESP which you already know is too high.

As others have told you there probably are other issues that your tech will find.

[Shophound]

I brought home a more accurate 0-1" Dwyer gauge. With the system dry, filter installed and only the blower running;
A = -.25
B = -.65
C = +.55
D = +.18

So I have a .40 drop across the filter and a .37 drop across the A-coil. Do these sound excessive?
Tech is coming to the house on Friday.

I see B & C as being your data points for ESP, which adds up to 1.2 ESP....hmmm, if so, any wonder the thing is freezing up?

[Jabarco]

You might find this article handy:

http://www.bacharach-training.com/Tips/esp.htm

Not sure about Jabarco's angle, but both the article and my own ESP measuring techniques involve using one static tip (or the static port on a pitot tube) to measure both locations. Thing to remember when using the Mag is to switch the hose from one port to the other when going from supply to return. As the article says, once you obtain both readings you add them together, ignoring the negative sign. That will be your ESP.

I read both of the articles and I found that they use one pitot tube. However, I was taught that to measure static pressure accurately, two pitot tubes are required. Furthermore, I was confused about using one pitot tube and adding the two readings. Either way, it appears that both ways work fine. Now we have determined that this unit has a high ESP which translates into low air flow.

Now that we have discovered the low air flow problem, I fear the frosted coil will be solved using the wrong solution like hundreds of HVAC tech do; overcharge the unit until the suction pressure is forced above 57 psi (or 32°F) to stop the frost from forming. Yes, the unit will start to cool again better than a unit with a frosted coil, but inefficiently, and at a much higher operating cost along with many other consequences.

Jabs

[Shophound]

I read both of the articles and I found that they use one pitot tube. However, I was taught that to measure static pressure accurately, two pitot tubes are required. Furthermore, I was confused about using one pitot tube and adding the two readings. Either way, it appears that both ways work fine. Now we have determined that this unit has a high ESP which translates into low air flow.

Now that we have discovered the low air flow problem, I fear the frosted coil will be solved using the wrong solution like hundreds of HVAC tech do; overcharge the unit until the suction pressure is forced above 57 psi (or 32°F) to stop the frost from forming. Yes, the unit will start to cool again better than a unit with a frosted coil, but inefficiently, and at a much higher operating cost along with many other consequences.

Jabs

You could be right, Jabs. Rather than hunt down the cause of high static, the endless supply of jug jockeys out there will just gas 'er until they get a pressure they like. I can't say I've never done that in the past before I knew better. :(

One of the articles seemed to say that taking each reading was more accurate. I guess the way to nail that one down would be to take two separate readings on the same system, then use two pitot tubes and take the readings again, then compare the two. If the two pitot tube method favored lower readings I'd tend to bias toward the separate reading results as being closer to actual conditions, due to the average quality of resi duct installations.

[dash]

I'm not sure the statics were taken at the correct places.


1.)Should be between the furnace and coil,not always possible.

2.)At the return inlet of the furnace,not blower inlet.

[VincentR]

I'm not sure the statics were taken at the correct places.


1.)Should be between the furnace and coil,not always possible.

2.)At the return inlet of the furnace,not blower inlet.


"Between furnace and coil".....I had to drill a hole.
"Return inlet of furnace, not blower inlet".....I had to drill a hole there also. I used my best logical judgement for each. I could be in a spot that is not the best I guess. I'll know tomorrow when the tech arrives.

[BigJon3475]

I hope the tech has the knowledges you are learning or his going to feel threatened as soon as he walks in the door and see's drilled holes for pressures. If you have maintenance plan with the company (may or may not don't recall if you said so) This may put the idea that you have been fiddling with the system. Not that you don't have the right to test your system but most companies or at least I would think most companies would be weary about this.

[VincentR]

OK,...tech came out this morning. It was cool today. 68 degrees outside temp, 73 in the house. Not quite optimum conditions for checking an AC unit I guess. He hooked up his pressure/temp gauges to the outside unit and had me kick on the A/C. From what I could see, the gauge on the left was showing the temp to be 27 degrees. Too cold. You guys were right, he says it was low on freon.
It took 1 pound, 3 ounces to bring the pressure/temp back into spec. He also checked out my static pressure readings and locations on the furnace unit in the basement and said they were correct. I couldn't watch for the SC/SH tests, I had another disaster to attend to, the pump for my pool filter decided to get jealous of the attention and let go. Made a horrible noise and a nice big mess. So I had to attend to that. He also mentioned that my ducting in the basement was not optimal, but I guess that is common. System should run normal now that it is charged. It was the first charge it took in 11 years.

[dash]

It likely has a leak,that started much more recently,so if he's back to add refrigerant soon,I'd get the leak found and repaired.