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.

[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.