Diagnostic Advice

[pehanlon]

Following readings were taken today on a RUUD 4-ton R-22 system:

Liquid Line
200psig >> ~101 deg F
80 deg F (reading taken near service valve)
78 deg F (reading taken about 6" from entry to evap)
I calculate 21 deg F SC (should not exceed 15 deg F)

Suction Line
50 psig >> ~30 deg F
77 deg F (reading taken near service valve)
I calculate 47 deg F SH (should be btwen 20-30 deg F)

Ambient Air = 79 deg F
Air Exit Condensor = 86 deg F
Air Temp Entering Evap at return air register near blower = 80 deg F
Air Temp Leaving Evap = 66 deg F

Condensor Coil and Evap Coil were cleaned two weeks ago. Have not taken amperage reading at compressor.

From Troubleshooting with Superheat at:
http://hvac-talk.com/vbb/showthread.php?threadid=49522

I read:

"A low side superheat greater than 30 degrees indicates too little refrigerant is in the low side.
· A condenser subcooling exceeding 15 degrees indicates too much liquid refrigerant is in the high side."

Further it states an example:

"High superheat with high condenser subcooling indicates a
restriction. Too much liquid is in the high side and too little in the low side."

Would I expect a restriction based upon the info above or could it be low on refrigerant?

[Toolpusher]

After I checked the blower wheel and filter.
And they both were clean.

I'd suspect the charge.

[HVAC Pro]

I'd say undersized piston or a TXV which isn't opening properly.

[pehanlon]

Originally posted by HVAC Pro
I'd say undersized piston or a TXV which isn't opening properly.

Evaporator has a sticker which reads "Unit equipped with piston #84." I'm not clear how to determine undersized piston when this came factory installed.

Could additional R-22 be added in limited quantity on the high side until the suction line temp begins to drop and then let the system stabilize and take new readings? Desire is for SH and SC readings to then be within acceptable limits or at least trending towards acceptable limits.



[Edited by pehanlon on 06-21-2005 at 11:12 PM]

[HVAC Pro]

I would pump down or recover and look inside to see if the piston or strainer is partially blocked. Then I'd pull the piston and look on the side to see if it is the proper size. (Number will be stamped on the piston.) I had a similar problem with a system last year. Turned out the piston was much too small. The sticker was right but the piston was the wrong size. I've also seen shavings stuck in the orifice partially blocking the opening, which would of course effectively reduce it's size.

[miami mike]

Look for frost.

Frost is your point of restriction.

Start at the metering device.

If your a Homeowner.....

Look for the Phone Book.

[pehanlon]

Originally posted by miami mike
Look for frost.

Frost is your point of restriction.

Start at the metering device.



No frost evident. Liquid Line just as it enters evaporator is cold to the touch but no frost. I would not expect a restriction and suspect undercharge but was hopeful Superheat and Subcooling info in the original post would provide basis for some sound diagnostics advice from this forum.

Any further advice is greatly appreciated.

[dnt]

Can you get the CFM and Static pressure for the supply duct also check the return duct for proper sizing and restriction. Low airflow (blower set to incorrect speed/dragging blower/restricted supply or return duct/etc.) can make it appear to be undercharged. 4 ton should be around 1600 CFM. Once proper airflow has been verified those posted readings might actually be useful. For better info list the following information; Unit design CFM and static pressure / Supply duct actual total CFM / Supply duct actual static pressure / Return duct size and return filter size with efficiency rating / Evaporator inlet WET BULB temp / outside ambient DRY BULB temp / low side pressure / low side line temp leaving evaporator / high side pressure / high side line temp at exit on condensor / temp at bottom of compressor housing / Dry Bulb temp at inlet of evap / Dry Bulb temp at outlet of evap / amp draw of compressor / condition of the klackenbocker (note: a klackenbocker can only be properly checked between the hours of 1:00 a.m. and 3:00 a.m.)

[jdenyer]

Originally posted by pehanlon

Originally posted by miami mike
Look for frost.

Frost is your point of restriction.

Start at the metering device.



No frost evident. Liquid Line just as it enters evaporator is cold to the touch but no frost. I would not expect a restriction and suspect undercharge but was hopeful Superheat and Subcooling info in the original post would provide basis for some sound diagnostics advice from this forum.

Any further advice is greatly appreciated.



Liquid line should not be cold, should be around room temp. Is there a filter/drier on the liquid line? If so I bet your restriction is there. As others stated pull the piston and check for debris, and right size.

[pehanlon]

Originally posted by dnt
Can you get the CFM and Static pressure for the supply duct also check the return duct for proper sizing and restriction. Low airflow (blower set to incorrect speed/dragging blower/restricted supply or return duct/etc.) can make it appear to be undercharged. 4 ton should be around 1600 CFM. Once proper airflow has been verified those posted readings might actually be useful.

Interesting comments as postings in the For Your Interest Fourm that speak to system efficiency discuss SH and SC but do not directly speak to CFM and Static Pressure.

I could see where that may be important in low air flow situations but the condensor, evap and blower fan are clean. Very good airflow from what I can tell although it has not been exactly measured. System is about eight years old and has been working fine until this cooling season.

I still suspect undercharge but am seeking advice from those well versed in SH and SC diagnostics.

[HVAC Pro]

So add some refrigerant! What are you waiting for? Use your digital scales and measure what you put in. If you don't get the results you like then go to the truck, grab the recovery cylinder and take it back out. Don't be skeeered. :D

[pehanlon]

Added R-22 today and took the following readings:

Liquid Line
275psig >> ~123 deg F
80 deg F (reading taken near service valve)
---------
43 deg F SC (should not exceed 15 deg F)

Suction Line
69 psig >> ~40 deg F
50 deg F (reading taken near service valve)
--------
10 deg F SH (should be btwen 20-30 deg F)

Ambient Air = 84 deg F
Air Exit Condensor = 99 deg F >> 15 deg F delta

Air Temp Entering Evap = 78 deg F
Air Temp Leaving Evap = 66 deg F >> 12 deg F delta

At this point I see low SH (10* vs 20*-30) and high SC (43* vs 12-15*F). This now indicates an overcharge from what I know. Agree? Any advice on how to tweak to get just right?

Thanks!

[NormChris]

self edit

Norm

[Edited by NormChris on 06-23-2005 at 10:11 PM]

[billva]

piston metering devices are charged by superheat.

airflow could be an issue, what is the duct size, including all branch ducts?

also wet bulb temps?

i do not see your credentials listed, that would help also.

[NormChris]

Originally posted by NormChris



I goofed up. Will repost.

Norm

[pehanlon]

Originally posted by billva
i do not see your credentials listed, that would help also.

Just updated....did not see that it was germane to my query for advice but I'm happy to provide that info. ;-)

[TheDuke]

I agree with the over charge now with the new readings also from the first readings I think you may have had a restriction in the refigerant lines etc.
but u can check see the condenser coil needs cleaning

here is what you can do now
to much refrigerant remove by recovery, some of the refrigerant and check the superheat.
if the superheat is low remove more refrigerant and if the superheat is high add refrigerant.
also note high efficient expansion valve systems may require charging by a factory subcooling chart.
you can also get amp rating for compressor and take amp draw to while chargeing on name plate good backup.

superheat example not trying to be funny just help
take low side pressure say 68 psig convert to temp 40f
now that = temp of line going into evap.
now take temp of line coming out of evap say 48f that =8f
superheat

[bmc]

It sounds like you have a restriction due to too small of an orfice. You stated the evaporator came factory installed with a #84 orfice, could it be that it's a universal 4-ton coil and need to match the orfice more closely with the condenser capacity? I've seen systems set up like this that work half-decent for quite a while until conditions in house or system change and this problem shows up.

[Edited by bmc on 06-25-2005 at 12:50 AM]

[mech890]

Origonally you had a partial restriction. Now you have a gross overcharge w/ a partial restriction. Fix it by finding the restriction and removing it.

[pehanlon]

Originally posted by bmc
It sounds like you have a restriction due to too small of an orfice. You stated the evaporator came factory installed with a #84 orfice, could it be that it's a universal 4-ton coil and need to match the orfice more closely with the condenser capacity? I've seen systems set up like this that work half-decent for quite a while until conditions in house or system change and this problem shows up.

[Edited by bmc on 06-25-2005 at 12:50 AM]

Assuming there is a partial restriction and #84 orifice is too small, what would be the best way to determine what the size of the orifice should be? I spoke to RUUD customer support yesterday and they stated they had no way of determining how to evaluate if a carrier coil is properly matched to a RUUD condensing unit. This system was installed eight years ago when the home was newly constructed.

I am able to resolve the overcharge but want to be able to address the possible restriction and undersized piston at the same time.

It appeared NormChris was going to post a reply but has not done so yet.

[Mr Bill]

Originally posted by pehanlon
I spoke to RUUD customer support yesterday and they stated they had no way of determining how to evaluate if a carrier coil is properly matched to a RUUD condensing unit.

This is some of the best advise you will ever hear so jot that down give that Ruud tech. support a gold star. :D

[bmc]

You must have spoke to the wrong person there, I mainly install Lennox and our tech support have charts that match condenser model numbers to proper orfice size. Surely Ruud has the same? The charts were made so they could sell you any make of coil and you could orfice it for exact match. Because of pressures stated and no evidence of frost, I think this is a possibility worthwhile checking into.

[smokin68]

RUUD could tell you what size piston came with that factory condenser.....if they can't chop it out and install a txv. Your problem is right there anyways......You now have an overcharge with a restricted metering device. There's no way around it....you have to open the system up. Adding freon is just going to fill your condenser up more.....good old mis-matches.

[madhouse]

Just forget the piston and install an adjustable TXV. Just tweaked my superheat. 92 deg here, good day to fine tune!

[tinknocker service tech]

why is refrigerant always the blame for a cooling problem
is the evape ciol clean or dirty. is the condensor coil dirty. what does the blower look like and is the blower motor working properly and at the correct speed. did the return flex if you have it clalasp. look at the entire system and do so checking. tunel vision will just cause more problems. now you may be over charged and when you lower it you will be back where you started and with the same question. check the entire system out and look for anything that may be causing this

[wendel]

May I suggest you calculate the BTU/hr the system is currently delivering. Here's a site that can supply all the data with minimal data input http://www.connel.com/freeware/psychart.shtml

If it's rated for 4 tons but delivering 2 tons of cooling, then a restriction/wrong piston seems likely. But if it's delivering 4 tons of cooling with only a 15 degree air temp difference, then maybe the system is undersized. The behavior would be similar.

[pehanlon]

Recovered some R-22 today and now have the following readings:

Liquid Line
250psig >> ~117.5 deg F
80 deg F (reading taken near service valve)
---------
37.5 deg F SC (should not exceed 15 deg F)

Suction Line
61 psig >> ~34.5 deg F
48.6 deg F (reading taken near service valve)
--------
14.1 deg F SH (should be btwn 20-30 deg F)

Last readings were 43 deg F SC/10 deg F SH so trend appears to be improving. Also took Relative Humidity readings in the home today using dry/wet bulb and got 57% RH.

Does this appear to now be a restriction, overcharge, or both?

[smokin68]

Are you going to keep playing around with the charge or are you going to find the restriction and fix it? You'll come back tomorrow "took more freon out and got these readings". It's only going to fix itself if whatever's causing the blockage miraculously dissappears. Good luck.

[Mr Bill]

Originally posted by bmc
Surely Ruud has the same? The charts were made so they could sell you any make of coil and you could orfice it for exact match.

Well Ruud don't! yes they do have a chart for Aspen or Ruud coils you go ahead and see if Ruud can tell you anything if you match a Carrier evap. with a Ruud condenser they will laugh at you, as most mfg.'s that don't want to be opening up a can of worms would do, now for Lennox :D no I won't go there I will leave that alone.

[tinknocker service tech]

one question is the unit cooling the house

[oogene]

poster stated that unit has worked fine for a few years (4?) but started acting up this season.Why are so many people blaming the piston??? how has it worked fine up until now then all of a sudden it is the wrong size ??? what am I missing ???

[mech890]

Since your having so much fun w/ the charge. Why don't you just pump the damn thing down. Pull the piston, look at it, while your there pull the coil and clean it. Make sure the piston is clear. Replace the filter drier, pull a deep vac and restart the damn thing? Apparently altering the charge isn't going to work or haven't you figured that out yet. Or better yet just replace the coil.

[tinknocker service tech]

like i said earler leave the charge alone till you find out what the problem is. with what you have done so far has proven till the problem is found you will never get the charge correct. pump it down and check the screen by the piston clean it. check the piston and put it back it worked for 4 years and dout if it realy madders if it is not the exact size. clean your coil and blower wheel. put back in service then see what you have.
better yet call the the guy that put it in and have him check it out

[pehanlon]

Thanks for so much advice. It is certainly helpful. Appears to me in reading all the posts/advice that the current best approach at this point is verify there are no restrictions (which requires system to be opened).

From there the coil can be pulled and cleaned and the system recharged and then evaluated using superheat/subcooling, amps, etc.

Thanks again.


[Edited by pehanlon on 06-27-2005 at 10:22 PM]

[grodan1]

I recently replaced an oriface that was oversized.After replacement I had readings like 240 over 40.I pumped the unit down again,took out the oriface and blew nitrogen through the lines.Put the same replacement oriface in and the systems pressures were fine.Situation like yours you need to pull all the refrigerent out and measure it back in by weight and then if pressures are not right you can start looking at all the other possible culprits.But take my advice for what its worth,I'm still very new to the field.