Lennox heat pump. Loud comp, low suction/head pres. what gives?

[mlock]

I have a lennox chp16-653-8y heat pump. Noticed it not cooling. Found the comp. hot as fire cracker. Put gauges on and found unit running 20 psi on suction and 160 on high side. Fan running, evap clean. Looked for a leak, found none, began adding r-22. Pressures didn't move, I didn't weigh it in, but guess about 2 lbs. Checked amp draw 18 at start up, drops to 10. Sure acts low on gas, but with pressure not moving I'm confused. Any ideas?

Thanks, Mel

[flange]

go back to the basics.........air flow, cleanliness, belt driven? maybe you are short o' gas. not sure of the lennox number, but depending on the size of the system, 2# may not be squat.

[airworx]

if you want to know if a system needs refrigerant then use subcooling. low subcooling means your low on gas.
then use superheat to troubleshoot. low suction high superheat low subcooling would mean low charge. so give us sub and superheat

[crab master]

What is your temp. differential across the indoor coil? Return air temp minus supply air temp. If it's 18 to 23 it's fine. Pushing/Anymore than 25 you've got air flow problems - check how many balancing dampers or diffusers are closed down, loose belt, broken fan blades, supply air ducted into return, bypass damper open, etc. Pressures, Superheat, subcool, Supply air, return air and outdoor temp would tell us a whole lot more. Taking superheat and subcool measurements and understanding them would make you a much better tech.

[bornriding]

Sounds like restriction to me.
recover refrigerant, purge system, pull vacuum, recharge with virgin refrigerant.

[crab master]

Bornriding
LOW HEAD AND LOW SUCTION RARELY EQUAL A RESTRICTION.
R-22 160 High and 20 Low.
Altough there could be a refrigerant restriction, that is not the root cause of this. I would be checking out alot more items before I charged the customer for recovery, new refrigerant, etc. Also what about finding the restriction? Maybe you figured it goes without saying, however I've known guys to do just what you've stated and then they wonder why it still doesn't work right.

[john dalton]

Dear Mlock,

The Lennox model #CHP16-653 is a 5 ton 208/230 volt 3 phase heat pump package unit with an EER of 9.6. The unit’s refrigerant charge is approximately 7 pounds – 7 ounces. Based on the limited information posted, I would “guess”, and that’s all it would be is a guess, that the system is extremely low of refrigerant.

The proper thing to do at this point would be to obtain all operating information, and then diagnoses the system based on that information, not guess at what it might, or might not be.

Although the subcooling, and superheat do need to be obtain, in order to do a complete and comprehensive job, all the pertinent operating readings need to be obtained, analyzed, and acted upon accordingly. Do not get into the “bad habit” of jumping to conclusions based upon “limited” information, such as subcooling and superheat alone.

In this case, I would not be surprised if the superheat was high, and the subcooling was low, which would indicate a refrigeration leak, but all the operating conditions need to be obtained before confirming that diagnoses.

The pertinent operating readings are as follows, if you have no way to obtain all of these, you should make an effort to obtain as many of them as possible to confirm a good and accurate diagnoses:

Discharge line pressure
Liquid line pressure
Suction line pressure
Liquid line temperature
Suction line temperature
Compressor FLA or RLA
Compressor actual amp draw
OSA
Return wet and dry bulb temperature
Supply temperature

Please post the results of your completed service call for our benefit………….

Respectfully Submitted,
John J. Dalton

[john dalton]

Dear Airworx,

Regarding your previous post:

“if you want to know if a system needs refrigerant then use subcooling. low subcooling means your low on gas…”

Although this statement is “sometimes” correct, it is not “always” correct, therefore it should not be used on this, or any thread at this forum.


“…then use superheat to troubleshoot. low suction high superheat low subcooling would mean low charge…”

Although these readings could indicate a system is low on refrigerant, it could just as easily mean that there is a refrigeration restriction somewhere in the condensing coil, or liquid line upstream from where the liquid line temperature was obtained.


“…so give us sub and superheat”

Giving us these two readings in and of themselves will not be sufficient for an “accurate” diagnoses, it could be used to make a guess or speculation as to the root cause of the problem, but after all is said and done, that would all it would be good for……a guess.

Respectfully Submitted,
John J. Dalton

[Shophound]

Lennox heat pump...low suction, low head. Adding gas doens't do squat.

Hmmm...I've come across this problem before. And not all that long ago at that.

It was the TXV at the evaporator. Power head failed, causing evap to massively starve for refrigerant. If you don't return much to the compressor from the evap, you won't have much for the compressor to make head pressure. As a result you get low suction, low head.

Go to the air handler and look over the coil and TXV. If you have a lot of frosting of the distribution tubes and return bends occuring but the coil isn't freezing over, and if you remove the thermostatic bulb and get no change in pressures when you immerse the bulb in hot water, I'd put good money on that TXV powerhead being history.

If it is indeed the TXV, be sure you replace it with one compatible with heat pumps. Many heat pump TXV's have built in check valves in the body for reversing modes.

[shogun8]

MLOCK, You may want to check the starter contacts for high resistance and the voltage on the line and load side. Also if the valves were bad we could have this same condition

[Edited by shogun8 on 07-15-2005 at 10:15 PM]

[crab master]

Shophound, this really does not make sense. I hope he finds the answer and clears the air. If the system has/had proper charge and you are adding gas to the system the gas has to go somewhere. A closed system and a positive displacement pump. If the txv is closed down due to blown powerhead/empty sensing bulb, then as you are adding gas you should watch your head pressure increase. If the compressors pumping and the internal relief isn't open and you have a restriction at your evap you will have an abnormally high head, low suction and high superheat-hot compressor.

[seaboard]

Originally posted by crab master
Shophound, this really does not make sense. I hope he finds the answer and clears the air. If the system has/had proper charge and you are adding gas to the system the gas has to go somewhere. A closed system and a positive displacement pump. If the txv is closed down due to blown powerhead/empty sensing bulb, then as you are adding gas you should watch your head pressure increase. If the compressors pumping and the internal relief isn't open and you have a restriction at your evap you will have an abnormally high head, low suction and high superheat-hot compressor.

It's been my experience that the larger the system the more refrigerant you will be able to stuff into it (with a bad powerhead) without raising the head pressure. Because refrigerant is not getting back to the compressor on the suction side (starved) the head pressure is unable to rise to a high level. Now if you were talking about a household refrigerator with a restriction then I would agree with your analysis that adding refrigerant would raise the head pressure.

Also this problem happens to be a heat pump and very often you can check for a bad powerhead by reversing the cycle and checking the operation in the heating mode. This also will put high pressure on the indoor TXV and if the powerhead seal is indeed back you will actually add refrigerant back to it (from the system). Therefore when you reverse back to the cooling cycle you may observe higher suction pressures for a period before the powerhead loses charge again.

[shogun8]

"Although this statement is “sometimes” correct, it is not “always” correct, therefore it should not be used on this, or any thread at this forum."Quote John Dalton

I can't believe this guy? Who the hell is he to tell another member what he can and can't say I thought we defeated the Nazis. John, Do every one a favor and take a hike!