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Doug L
19-07-2012, 05:26 PM
Hi All
I have a Lennox HP26-036 heat pump with an ECB29 Air Mover. AC runs for ~30min and then the compressor shuts down. The contactor remains closed (220V at compressor terminals), so it is shutting down on overtemp. Fan remains running. Using the Approach Method to judge coolant level, I get interesting readings. When the unit powers up (on cool), the dT (well temp - ambient{26.2C - 21.3C}), is 4.9C (recommended 5.8+/-0.5C), so a little low indicating remove refrigerant. The refrigerant charge has not been altered for some years. Approximately 30 minutes after start up the well temp dropped slowly down to 22.8C and then over the space of a minute rose to 30.3C at which time the compressor overtemped. I am assuming this excursion is caused by the TXV in response to something?? Any thoughts would be appreciated.
Thanks
Doug

chemi-cool
19-07-2012, 05:36 PM
Your compressor shut's on internal clixon could be seized, when such thing is happening, it will never be ok, replace it and check the new one for working conditions.

The Viking
19-07-2012, 06:28 PM
Doug,
I take it from your post that you are the end user and not an engineer working on this kit for a living?

Looking at your post there are a lot of reasons why this might happen but to determine what is going on inside your system you need a professional with his (or her) hands and tools actually on your system, sorry.

From a financial point of view the cheapest option will also be to get a professional in to have a look. We could say to replace the compressor only for you to later find that the compressor was OK but the charge was missing or the contactor faulty...

:cool:

.

Doug L
19-07-2012, 06:30 PM
Hi chemi-cool
Thanks for your reply. The clixon seems to be operational (if I let the compressor cool it closes). It could be opening at a lower than designed temp though. As the well temp increases in that last minute, the surface of the compressor also rises in temp since the coolant entering the compressor is warmer thus less compressor cooling. When the clixon opens the compressor is quite hot, so I suspect the clixon is doing its job. Unfortunately the clixon is internal and so would mean replacing the compressor.

Doug L
19-07-2012, 06:35 PM
Hi Viking
Thanks for your reply.
You are right that I am not currently doing this for a living, but I did spend a couple years in the industry, and have all the tools.
Doug

The Viking
19-07-2012, 11:40 PM
Hi Viking
Thanks for your reply.
You are right that I am not currently doing this for a living, but I did spend a couple years in the industry, and have all the tools.
Doug


Ah, good. Let's start again...

As the compressor is running for a period before it cuts out, what are the:
-Discharge pressure?
-Suction pressure?
-Discharge temperature?
-Liquid line temperature? (Both where it leaves the condensor and before it get to the expansion device)
-Suction line temperature?

Oh, one last question... What refrigerant is it operating on?

.

Doug L
26-07-2012, 06:05 AM
Hi Viking
Sorry for the delay, we had a plant shutdown.
I have taken the suggested readings:
Ambient Temp 25.4C refrigerant is HCFC-22
-Discharge pressure 150 psi
-Suction pressure 54 psi
-Discharge temperature 66.4C
-Liquid line temperature where it leaves the condensor 28.8C
-Liquid line temperature where liquid line leaves outdoor unit 28.2C
-suction line temperature 20.7C just as it enters compressor
-suction line temperature 19C where it enters outdoor unit

After about 30 minutes the readings changed rapidly and the compressor tripped out:
-Discharge pressure 140 psi
-Suction pressure 10 psi
-Discharge temperature 120.5C
-Liquid line temperature where it leaves the condensor 24.3C
-Liquid line temperature where liquid line leaves outdoor unit 24.0C
-suction line temperature 54.7C just as it enters compressor
-suction line temperature 24.2C where it enters outdoor unit; I am not sure of this last temp as the compressor stopped a few seconds before I measured it.

Thanks again for your help
Doug

monkey spanners
26-07-2012, 08:37 AM
I think its the reversing valve leaking discharge gas back into the suction. Can be the only way I can see the suction temperature getting that hot as it enters the compressor and not changing as it enters the unit. Are your pressures the true pressures the compressor sees or are they after the gas has been through the reversing valve?

The Viking
26-07-2012, 08:25 PM
R22 @ 150psi = a saturated temp of 28.3ºC. A pipe temperature of 28.XºC gives no sub cooling what so ever, indicating a shortage of refrigerant.

R22 @ 54psi = a saturated temp of -1.7ºC. A pipe temperature of 19ºC gives a superheat of 20.7K!!! Indicating a shortage of refrigerant or a faulty expansion device and further more, giving no cooling for the compressor what so ever.

M S, I am awfully sorry but in this one case I have to disagree with you.:eek:
If the reversing valve were letting by, the likelihood is that the suction pressure would increase, not drop.
Doug, when you say "just as it enters the compressor" am I right in assuming that this reading were taken within 1" of the compressor shell?

Doug,
I can not say what happens after 30 minutes but to me, sitting some thousand miles away from your system, the root of your problems is that the system is short of refrigerant.
You most likely got a leak somewhere on the system, as it seems to be a small leak it is probably somewhere on the suction side.
The best way forward would be to find and repair the leak, give the system a good deep vacuum and then recharge it with the right amount of R22. You should then see the sub cooling to be around 6-8K, the superheat to come down to around 4K and the compressor discharge temp to stay below 100ºC.

:cool:

.

monkey spanners
26-07-2012, 09:08 PM
Reading it again i think Viking has it correct :o i was just focusing on the jump in temperature of the suction line but it could be heat from the compressor if you are measuring too close to the compressor.
Looking at the discharge temperature this is in the range that could cause a discharge thermistor or klixon to trip.

Doug L
21-08-2012, 04:53 PM
Hi Guys
I have now added refrigerant and have new data (sorry for delay).
I added refrigerant in 2 stages 0.2 pound (by weight) each. After the first addition I thought all was right as it ran for an hour, but then suddenly did the overtemp thing again exactly as before. I added another 0.2 pound and it went back to 30 minutes before another overtemp event. Granted I did not add much refrigerant, but all the time I was adding it, the advance method (recommended by Lennox), the measurements were telling me it had sufficient refrigerant. As in the previous post:

Ambient Temp 25.4C refrigerant is HCFC-22
-Discharge pressure 150 psi
-Suction pressure 54 psi
-Discharge temperature 66.4C
-Liquid line temperature where it leaves the condensor 28.8C
-Liquid line temperature where liquid line leaves outdoor unit 28.2C
-suction line temperature 20.7C just as it enters compressor
-suction line temperature 19C where it enters outdoor unit

After about 30 minutes the readings changed rapidly and the compressor tripped out:
-Discharge pressure 140 psi
-Suction pressure 10 psi
-Discharge temperature 120.5C
-Liquid line temperature where it leaves the condensor 24.3C
-Liquid line temperature where liquid line leaves outdoor unit 24.0C
-suction line temperature 54.7C just as it enters compressor
-suction line temperature 24.2C where it enters outdoor unit; I am not sure of this last temp as the compressor stopped a few seconds before I measured it.

there seems to be no indication of low refrigerant until the sudden onset after 30 minutes. I am adding in the suction port and so the event is over before I can add more.
I was wondering about the expansion valve and the possibility that it is being plugged by debris in the refrigerant (I have no experience with this type of problem).
Thanks again for all your sage advice.
Doug

Doug L
24-08-2012, 06:11 AM
I reread the interesting thread started by Larry2 in 2006. He had a very similar issue with a very similar Lennox heatpump. In the end he had an incorrect run capacitor value forcing the compressor to run less efficiently, so more heat. I measured my capacitor at 45uF but it was labelled 50uF +/-5% or 47.5uF to 52.5uF. 50uF is the appropriate value for the compressor. After much referral to my old but thorough text books, I satisfied myself that a 10% lower capacitor value would cost me only a percent or 2 in efficiency, and sadly decided I was barking up the wrong tree. I will next try iceing or heating the sensor bulb for the expansion valve to determine if it is in fact working. I have a USB data acquisition board that allows me to record 8 temperature sensors, so after that I will try spacing them along the evaporator tubes to see what transpires in that minute when the pump quickly heats. Any comments on that would be appreciated.
Doug

Mrdaikin
24-08-2012, 02:00 PM
You need to weigh out the refrigerant not top it up!! It's def low and has a leak which will require repairing otherwise you will be spending your life there topping it up!!

Mrdaikin
24-08-2012, 02:11 PM
Does it have a liquid line solenoid valve/ coil? If so does it look damaged in any way like cracking? When the unit pressures begin to drop check for temp drop a cross your liquid line components. If it seems like its running fine then all of a sudden your suction drops from 60psi to 0psi then your liquid line could be shuttin and causing pump down

Doug L
25-08-2012, 04:03 PM
Mrdaiken, thanks for your reply. It is a relatively simple system with no valve in the liquid line. The only valves present are the reversing valve and the expansion valve.