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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.
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.
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?
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).
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?
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.
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.
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.
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.
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.
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.