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Old 01-14-2012, 09:16 PM   #1
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heat pump freezing problem


I would like some other opinions on this issue I am having with my American Standard Heritage 10 heat pump (r22) system that's about 10 years old. I am thinking there is moisture in the refrigerant lines that is causing it not to function properly in the heating mode.

The system works perfect in cooling mode, but not in heating mode. About a year or so ago, I had a technician add refrigerant to the system, and since then, it has been performing great in air conditioning mode, but this winter, when I put it into heating mode, I am not getting any warm air inside. I removed the cover on the outdoor unit, and noticed the expansion valve on the outdoor unit was all frosted up, and the first coil loop was icy as well, but none of the other loops. I activated the reversing valve to put it in AC mode, and the reversing valve functioned properly, giving a hiss. After leaving it like this for a few minutes, the ice went away, so I switched it back to heating mode, again, it hissed. This time though, I noticed that it worked properly for a while. I touched the hot gas line going inside, and it was good and warm. I went inside and felt the output, and it was warm. Several minutes later though, I noticed it was back to the same old same old, with the expansion valve coated with ice.

I had a service tech look at it a week or two ago, and he connected his gauges, added another pound of refrigerant, and said the reversing valve is not working after he noticed the high head pressure, and very low suction pressure in heat mode, but perfect pressures in AC mode. I didn't think this was the case, as I could hear the hissing of the refrigerant as the valve changed modes, and the fact that the valve is de-activated in the malfunctioning heating mode, but activated in the functioning cooling mode. The tech stated that it would be too expensive to repair, and I should replace the system.

I found an old R12 gauge set in my garage and connected it up to the service port to see what was up. I figured what do I have to loose now. When I first started up the system in heating mode, I noticed that the pressures were good...about 240psi on the high side, and about 70psi on the low side. I grabbed the expansion valve bulb and warmed it with my hand. I could see the pressure go up as the valve opened. I left my gauges on the unit while it was running and watched it. As the unit ran, the low side slowly dropped, and the high side increased. I grabbed the bulb again, but this time, the pressure didn't rise, but continued to drop. I also noticed that the hot gas line back into the house was getting cooler. The low side pressure dropped to about 10psi, and the expansion valve and output lines began getting a coating of ice on it. I then activated the reversing valve. Pressures were perfect in AC mode, so I switched it back again. The process repeated itself...perfect pressure in heat mode for the first few minutes, and then it fell off.

Based on my testing here, the expansion valve is good, but getting clogged when moisture in the refrigerant loop freezes inside of it. The interior coil has capillary tubes, so it doesn't freeze up when in AC mode. Does this hypothesis sound correct?

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Old 01-14-2012, 09:50 PM   #2
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heat pump freezing problem


check the dryer in the heating mode might be restricted if you feel a temp drop going to the condenser....it's not moisture that is making the ice start showing it's a retriction just enough to meter it so the pressure drops and then the temp on the pipe.use a cup of ice water and the hand test next time on the TXV and just watch the suction react...that whushing when the reversing valve slides is a good sound.the discharge pipe should be super hot and not able to be grabbed if the charge is right the TXV modulates to that bulb in hand test check the dryer for chilling out to that condenser in the heat mode...txv is starving for liquid coming back from your air handler at 10psi hi head and lo suction are an indication of a retriction on that LL

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Old 01-15-2012, 04:03 AM   #3
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heat pump freezing problem


Basically, only way it would b a moisture problem, is if you have had work done to it that required the system to be opened. was the system opened since last winter?

If not, a restriction is your most likely culprit.
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Old 01-15-2012, 11:06 AM   #4
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heat pump freezing problem


Some heat pumps have a heating element built into a portion of the coil that assists the unit when temps fall below range. On most you cannot see it but look for wires attached to the coil and follow them back to the outdoor controls there should be a thermostat that controls it. If it has them the thermostat or element could be bad. Test thermostat for voltage thru ti and element for continuity and to ground disconnected with unit off.
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Old 01-16-2012, 04:27 PM   #5
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heat pump freezing problem


Here's a picture of what is happening when it's freezing up. The section of line between the dryer and the expansion valve is actually lukewarm. The freezing, as you can see here, isn't starting until the expansion valve. I was at first thinking the check valve was leaking, but it seems to be okay. The other side of it is lukewarm
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Old 02-01-2012, 05:44 AM   #6
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heat pump freezing problem


I have the same problem with my Heritage 10. Mine works fine in heat mode when temperatures are sufficiently above freezing (> 38 F). If temps are below that, performance deteriorates after a defrost cycle, but not due to frost on the coils.

I'm also suspecting moisture freezing up and restricting coolant flow.

Please let me know how you fare.
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Old 02-01-2012, 08:53 AM   #7
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heat pump freezing problem


there's not enough moisture compared to the actual charge that makes frosting.the TXV is a resticter thats how you get the refrigeration effect in either mode(cap tubes do the same) that restriction is so big it is causing a suction pump down and hi head try ice and hot water test on the TXV bulb during run...tap the power hat and TXV body as it is modulating between cups on water
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Old 02-01-2012, 08:12 PM   #8
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heat pump freezing problem


bad heat txv
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Old 02-02-2012, 07:16 PM   #9
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heat pump freezing problem


You called it! The TXV was bad. I had the air conditioner technician at the house Monday. He hooked up his gauges and noticed it was low on refrigerant. He then got out his leak detector and probed around the compressor, the lineset and the air handler. He found a leak right around the compressor on the discharge line. He also found a leak where the discharge line runs under the coils to the reversing valve. Today, he came and repaired all those parts, charged up the system and guess what, the expansion valve did it's same thing! I was thinking for sure the system would start working correctly. I explained everything I stated in my first posting to the tech too prior to him visiting on Monday too. Well, I can't complain. He's putting an expansion valve on the thing for free because mis-diagnosed the problem. So I am getting two repairs done for the price of one!

I do note that this was a different technician than inspected the unit on the first service call too!


Last edited by av-geek; 02-02-2012 at 07:20 PM.
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