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Regan Land
Regan Land, HVAC Technician
Category: HVAC
Satisfied Customers: 647
Experience:  Over 20 years of experience, NATE Certified, Licensed HVAC Contractor, Certified IAQ Specialist
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HVAC (Heat Pump) Question I have a 2-year old Trane XR13 single

Customer Question

HVAC (Heat Pump) Question: I have a 2-year old Trane XR13 single stage heat pump with a two-speed air handler and electric back-up or "emergency" heat, in Central Florida. The unit works fine in cooling mode, but not in heat mode. The blower motor starts as required, but neither the condenser fan or compressor start at all. If I swith to cool mode and then back to heat, the condenser fan and compressor will start and run for anywhere between a few seconds to a few minutes and then quit and not restart, while the blower keeps running. I've checked the thermostat wiring and even installed a second thermostat, to no avail. The reversing valve also seems to work fine (thermostat sends current to solenoid on cool mode, none on heat mode, and solenoid seems to click as necessary, you can also hear the gas pressure release when the reversing valve solenoid switches from heat to cool. Last winter I had a friend who's an HVAC tech (unlicensed) check charge, and he said it was a little low and added some freon, but it made no difference.Two days ago with about 70 degrees OD temperature I got the heat to run for several minutes after switching back from cool mode, but now with temps in the 30s to 50s, it will only run a few seconds, and only after switching back from cool mode. Yesterday with OD temp about 55, heat ran for a few minutes, then condenser entered defrost mode, seemed to complete as required, and resumed heating, but only for a few seconds. That was the end of it. Could it be some sort of faulty pressure or temp sensor, or the defrost board? If the reversing valve was sticking or partially sticking, how long would it run in heat before cutting off? What else could it be? How can I troubleshoot? Is there a way to bypass for now to run heat at least temporarily with no need for cool? Thanks.
Submitted: 6 years ago.
Category: HVAC
Expert:  Regan Land replied 6 years ago.

Hello. Welcome to My name is XXXXX XXXXX I'll be happy to assist you today.


There are several things that can cause this, some of which you already said above. My guess is a bad outdoor TXV (or check valve on the indoor TXV). To accurately help diagnose this, we will need to know the refrigerant pressures as well as the indoor and outdoor ambient temps during the time the pressures were checked.


Also, put your meter between C and Y outside and see if you are getting 24v when the thermostat is calling, but the unit isn't running.

Customer: replied 6 years ago.
Thanks, XXXXX XXXXX was just outside installing a new defrost control board. No dice. I will try to get the pressures and temps for you tomorrow. In the meantime, can you tell me exactly which C and Y you are talking about? Yellow and Common? To check the pressure switch?
Expert:  Regan Land replied 6 years ago.

Yes on the common and yellow part. This won't check the pressure switch, but will tell us if the condenser is getting a signal from the thermostat come on.

Customer: replied 6 years ago.
Ok. I still won't be able to get you pressures until tomorrow, but I confirmed thermostat is sending signal. I also jumped the low pressure cut off switch terminal (from the defrost control board to the contactor, after the unit had shut down, and it started and ran. Does that mean it's the low pressure switch shutting things down, or is there also a high pressure switch on this model? I only see two temperature sensors on the small pipe coming from the compressor. If so, would the faulty TXV cause the pressure to fall below preset limit or could it be a bad switch? Is there a way to test the switch or the TXV, or is that just done with the pressures? I realize this is getting involved, so if you can help me out, I intend to throw in a bonus. Thanks.
Customer: replied 6 years ago.
Finally checked pressures. Ambient was about 55, inside was 67. On cool mode: Low side: 62 psig; High Side: 120 psig. Also, resistance measured through the low pressure cut off switch was between 30 and 50 while in cool mode, but dropped to 8 to 15 in heat mode. Again, if I run power directly from the lpco terminal at the defrost control board to the low voltage contactor, the unit fires right up. Am I just low on charge?
Expert:  Regan Land replied 6 years ago.

If you have an R22 system, it doesn't look like low charge... if you're not sure if it's R22 or R410A, take a look at the model #. If the model # XXXXX with a 2, then it's R22, if it starts with a 4, then it's R410A.


It could still be a bad TXV. We will need to know the pressures in heat mode as they aren't listed above. Does the suction drop? What does the head pressure do?

Customer: replied 6 years ago.
It's R22. I'll try to get the heat pressures to you later. I've read about holding the expansion bulb in your hand and then placing it in ice water to see if the pressure changes, in order to check the TXV. Does that work and will it work in heat mode, and should I hook up the gauges by the reversing vavle instead of outside by the access panel? Thanks.
Expert:  Regan Land replied 6 years ago.

Sorry for the delay... I was trying to answer, but the site was having problems, so my answer never went through.


The outdoor TXV is what is used in heating. Heating up the bulb will open the valve, and cooling it down will close it. If the valve is stuck, or the bulb lost it's charge, heating and cooling the bulb won't change anything, but it's worth a shot.


You will need to put your suction hose on the tap that's between the reversing valve and compressor. You can put the high side on either of the service taps as the pressures should be relatively close. I would recommend placing it on both (obviously one at a time) so that we can better determine where the restriction is (if there is one).

Customer: replied 6 years ago.
Regan: No problem on the delay. Thanks for looking into it. I will gladly accept your answer, but want to be able to ask more questions. What should I do? Anyway, I had a retired tech come by and charge the unit and it fired up and ran fine-for a couple of hours. He says it has a leak, but wasn't sure where. I got it to run for a few minutes again, and I hooked up the gauges where you said, and on heat mode suction went all the way down to 10 or 15 psig, and head pressure goes to about 120. That's with ambient about 50 degrees and inside about 67. Unit is back to starting for about 2 seconds and cutting off. Cool mode runs, but I will have to recheck those pressures by the reversing valve. It would have to be a hell of a leak to lose that charge that quick wouldn't it? Is there a way to check the outdoor TXV?
Expert:  Regan Land replied 6 years ago.

The test you're doing is the best way to test the outdoor TXV.


The symptoms above could indicate low charge or TXV... we'll need the unit to run longer to know for sure which. Can you locate the low pressure switch (it will be on the suction lie between the reversing valve and the compressor)? Let's bypass that by cutting the wires and connecting them together with a wire nut. Be sure to leave enough wire from the switch so that you can connect the switch back after we're finished.


After you bypass the switch, check the charge again. Let it run for a bit and see if the suction pressure starts to rise or if it drops down to a vacuum.


Do you know how much refrigerant was added?

Customer: replied 6 years ago.
Ok. I'm not home right now, but will be able to do that later this afternoon. I don't know how much refrigerant, but the tech is an old timer who didn't check any temps; just his gauges, and said the suction pressure was really low, so it was very low on charge. That is suspicious to me , though, because if it were that low, wouldn't it fail to run on cooling mode too? One more thing: How long is it safe to let run with the low pressure switch disabled?
Expert:  Regan Land replied 6 years ago.

If it were low, it would be obvious in cooling mode, but may not be low enough to trip the low pressure switch (pressures will be higher with warm outdoor temps).


You can leave the unit running with the pressure switch disabled as long as the suction pressure doesn't drop below 0 (vacuum) for a long period of time. The compressor will have an internal overload that will shut it off before it overheats.


Did the tech put his high side on? If not, he wouldn't be able to know if the suction pressure is low due to low charge or bad TXV. If so, I question weather or not he knew what he was looking at.

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Customer: replied 6 years ago.

Yes. He checked high side. Again, his diagnosis was low charge, but he didnt' seem very confident when leak checking, so I am questioning everything. If the TXV was bad, what would the high side show on heat mode under the previous scenario? I think it was about 140.

Expert:  Regan Land replied 6 years ago.

If the unit continues to run (and TXV is bad), the high side will rise and the suction side will fall. If it's closed completely, the high side could reach into the 400 psi range and the suction could go into vacuum.


If the high side remains 140 and the suction remains 15, then I would say low charge as well.

Customer: replied 6 years ago.
Cool. I'll check it out. Thanks.
Expert:  Regan Land replied 6 years ago.
No problem
Customer: replied 6 years ago.

No need to reply tonight. Ambient temp 50, inside house 65. Disabled low pressure switch to allow unit to run in heat mode and pressures were: Heat mode pressures: 15 psig suction, 125 high side. Added about 1.5 pounds more r22 to see if unit would run in heat mode, but it only ran about 2 minutes. After adding r22: 18 low side, 145 hight side, but would not run unless pressure switch bypassed. Pressures in cool mode: 75 suction, 225 high side. When first switching to cool mode the high side steadily increased to about 300 and then stabilized at about 225. Suction side did not move that much.

So is it likely a big leak somewhere or something else? I'm calling a tech tomorrow, but I would like to have an idea as to what the problem might be, so I don't get taken for a ride. Thanks.

Expert:  Regan Land replied 6 years ago.

I'm still thinking restriction. Your pressures in the cool mode are high for those ambient temps, so it's likely overcharged now.


It's looking like the outdoor TXV, but I would need to know what the pressure is at the suction service valve when the system is running in heat mode. Keep in mind that both the suction and discharge will be high pressure when in heat mode, so switch your high side hose (keeping your suction hose on the all time low port).


If the pressure on the suction and high side lines are about the same, then we know the indoor TXV is checking like it's supposed to. If the pressure at the suction port is a lot higher than the liquid port, then the problem is the indoor TXV.

Customer: replied 6 years ago.

Regan: To recap: Diagnosis of the first guy who came out to check it (retired dude): Leak in evaporator (based on his cursory leak detector test which entailed just sticking his probe in the plenum upstream of the coil while blower was running). Charged the unit and it ran for a few hours. Diagnosis from second company I called out: Leaking evaporator coil and bad TXV. This was a "free estimate company, so I was sceptical.


Diagnosis from third company I just had out this morning: Bad outdoor TXV. $575 to replace under warranty (labor charges only). They want another $104 to leak test the indoor coil, or they will just replace the indoor coil at the same time, for another $160 under warranty, based on first two diagnoses. Are these fair prices, and should I just replace the indoor coil for an additional $160, since it will cost me another $104 just to find out if it leaks or not? Thanks.

Expert:  Regan Land replied 6 years ago.
$575 is quite a bit to replace a warranty part, but it covers labor, uncovered parts (filter/drier, refrigerant, etc), vacuum, welds, etc, etc. $160.00 to replace a warranty coil is a steal, so I would tell them that you want to add that, but only want it to be done if it's leaking. That way, they'll have to leak test it on their own dime and you won't be responsible to pay for the leak search, even if it isn't leaking. If they really want to earn your business, they won't charge you for the leak search if they don't find a leak. I would not let them replace the coil without doing a leak search.