ive been working on a buddies ac unit whenever something goes south. he has a ducane heat pump. cools great in the summer, but wont make heat in the winter. my first thought was he had a bad reversing valve. it seems to be working fine.

when we turn the heat on, it kicks on for about a minute and then shuts down. at the same time, i notice that the txv valve is iceing over. while it is running, the evap gets warm, and condenser gets cold. shuts down, and after about 10-15 minutes it will start and run for another minute.

ive read a couple different things, one says its low on freon. i could see that if it had problems in the summer.

another said it could be the pressure switch, but again, it works fine in cool mode.

im good with the electronics side of working on it, but ill end up calling someone in if it looks like the system needs to be opened up.

im hoping someone on here may be able to shine some light on it.

tstat is brand new. he wanted to switch to a programmable. swapped it out, still same issue.

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have no worries.....President Obama swears "If you like your gun, you can keep it

Not an HVAC tech, but I did take an hvac class in college once.

How well did it heat before? Is this a new development?

From the description it sounds like this heat pump uses outside air as the heat sink. That type of heat pump is notorious for not working worth a poo when ambient temperatures get to about freezing or lower. How cold is it there?

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

they bought the house in september two years ago. it didnt work then, but it didnt bother them. they have a newborn now, and the little bit of heat the fireplace puts out isnt enough for the baby. its getting into the 40s at night. even in the 60s it wont work. i started working on it at 2pm today.

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have no worries.....President Obama swears "If you like your gun, you can keep it

PM ' VStech ' On here. he's HVAC certified if memory serves correct

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

Had similar problems with ours recently, a 15 year old Trane 2 1/2 ton.

According to the tech that serviced it, if the unit is more than a few years old, low freon from gradual leaks is usually the main culprit for poor performance.

2 or 3 weeks ago, starting the day after the utility had dropped power the night before for 2 or 3 minutes, the beast would be iced up badly - like 1/8" of solid ice inside and out - with temps in the 50's outside - and the defrost cycle couldn't make a dent in it. We'd have to turn off the system and let the ice melt on it's own.

Service tech discovered it was 3/4 of a pound low on freon - which in his opinion was nowhere near low enough to make it behave in such a way, given the temps we'd seen.

His considered guess was that many of these pumps have to "learn" how long to run the defrost cycle to deice themselves - and considering that this had started the day after the utility had dropped power - that this had reset the defrost cycle to minimum, and it would have to relearn how long to run the cycle before it would behave normally again.

The other possibility was that the power transient had damaged the control board and it wasn't operating properly. Only time and observation would tell.

It kept doing this intermittently, and the other day I discovered the reason why. Temps in the high 40's/low 50's, it was iced up again. I turned off the system for a couple hours and let the ice melt. When I turned the system back on, the pump fan bumped for a couple revolutions, then stopped, and the unit kept running. With no air flow over the coils, it immediately began freezing the moisture out of the air and forming another sheet of ice on the coils, fast enough I could watch it forming and thickening.

I turned the system off again, and this time let it set for several hours. When I turned it back on, it behaved normally - and has continued to do so for the past 3 days, even with temps dropping into the high 20's, no hint of ice forming.

My guess is a faulty control board or a old worn out start capacitor for the fan motor.

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Just say "NO" to Ethanol - Drive Diesel

Mitchell Oates
Mooresville, NC
'87 300D 212K miles
'87 300D 151K miles - R.I.P. 12/08
'05 Jeep Liberty CRD 67K miles
Grumpy Old Diesel Owners Club

faulty control board i could believe. its not a bad cap or motor. those are new as of last summer. this has had this issue for two years. cools just fine. that rules out the cap and motor.

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have no worries.....President Obama swears "If you like your gun, you can keep it

Probably right but you know the rule about assumptions. If something else made it fail the first time it could be going again.

General troubleshooting rules apply. Keep your eyes open and that means all of your senses.

Measure everything you can, temps, pressures, air flow, amps, volts etc. Before and after each component.

If you don't have a good clear understanding of the following terms, read: subcool, superheat, latent heat, sensible heat. It is difficult and costly to heat or cool humid air.

You have to figure out where the refrigerant is and what it is doing compared to what it is supposed to be doing. Where is is it a liquid, gas or in between?

Very rough rule of thumb is to look for 20°F changes across components.

Often oil leaks where refrigerant leaks.

Easy to overlook power problems and dirty coils.

Good knowledge to save some bucks, time and discomfort.

The universal certification took me 3 weeks of self-study and cost $65. Now I can buy wholesale. Get the certification through a wholesaler. I am not a professional HVAC person.

ended up being the txv.

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have no worries.....President Obama swears "If you like your gun, you can keep it