Ask Me Help Desk - Heat Pump going into defrost prematurely

I have a 20 year old 2 ton York E1FH heat pump with TXV on outdoor unit, but no TXV on indoor coil.

The unit is prematurely entering defrost when in heat mode. Depending on the outdoor temp it is entering defrost at least every 15 minutes.

I have 3 service ports two that leave the unit 3/8 liquid line, 5/8 vapor; and a third that taps just above the accumulator. I was told to use the third for suction.

With the following conditions of outdoor temp 74°F, indoor temp 73°F and RH 31%, here is what I am seeing in each mode:

In cooling mode: suction 65 PSIG w/temp 69°F, 5/8 vapor line 140 PSIG w/temp 45°F, 3/8 liquid line 145 PSIG w/temp 67°F. Delta across the indoor coil is 18°F, precisely what is was when the unit was checked out to be okay 3 years ago under the same conditions. The delta across my coil looks good but I was told the high side pressure seems too low.

In heating mode things are not so good: suction 60 PSIG and quickly plummets to 15 PSIG w/temp steady 67°F; 5/8 vapor line 150 PSIG w/temp 90°F and quickly rises to 250 PSIG 110°F. Delta across the indoor coil is near zero. I notice frost quickly building up on the TXV and beyond into the outdoor coil. The liquid line sensor is clipped at this point, so it is no surprise the unit thinks a defrost is needed. Compressor amps appear to be a little low by 1-3 AMPS when I can get a steady reading.

There is no appreciable temp drop across my filter dryer, so I think there is no block there.

My reversing valve, which actuates for cooling mode, appears to be sweating on the correct pipes but I am not sure how to check it in heat mode.

I have added 1 lb of charge thinking I had a leak, but nothing has changed.

When the unit has not run for some time my PSIG matches the outdoor temp. I was told this means I have few if any non-condensable.

I am suspect of the TXV and have removed and cleaned the sensing bulb to no avail.

I am learning as I go and could use some ideas. Could my TXV be bad? If so, how to diagnose it further? Could my reversing valve be bad at rest? If so, how to diagnose it further? Could I have a blockage somewhere else? Is it possible I am still low on charge?

Thanks for any guidance.

Replace defrost timer and or defrost timer sensor. If old defrost timer has a setting switch or jumpers set the new one the same as the old. Then contact a HVAC company so they can come out and remove the excess refrigerant you installed unless you have your own reclaimer machine. NOTE: it is against federal law to discharge refrigerant it must be reclaimed. It seems you have created your own problem since the defrost circuit was causing your problem to start with. It is also possible you have noncondensibles in the refrigerant system.

Quote:

Originally Posted by hvac1000

Replace defrost timer and or defrost timer sensor. If old defrost timer has a setting switch or jumpers set the new one the same as the old. Then contact a HVAC company so they can come out and remove the excess refrigerant you installed unless you have your own reclaimer machine. NOTE: it is against federal law to discharge refrigerant it must be reclaimed. It seems you have created your own problem since the defrost circuit was causing your problem to start with. It is also possible you have noncondensibles in the refrigerant system.

Thanks hvac.

Yes, I may be a little overcharged but I did not mention I had a bad high side schrader I replaced that did leak some while I was debugging that issue. Plus all the gauge hook ups I have probably lost some. But I am really wondering about the 15 PSIG suction.

The liquid line sensor is new. I even checked the sensor with an ice bath and it follows proper resistance curve. The timer is embedded in the YorkGuard Control module, and is no longer made. There is an upgrade but that would be would be introducing an upgraded module to our unknowns. The algorithm is time plus liquid line sensor, and I can't seem to get an answer as to which prioritizes.

Is it still possible I have noncondensibles when at rest the PSIG matches outdoor temp?

The system read 15 PSIG suction before I added any refrigerant. I have gotten some strange readings from suction. Early on when I was checking out the system it read 40 PSIG, and is now 15. I did not change anything or touch anything, but something changed on its own. That number seems very low to me. What do you think?

I also checked something yesterday. When in head mode I checked temps with my laser thermometer across the reversing valve and everything was reading very just about to the same hot temp temp. this does not seem right to me as the compressor discharge should be routing to one direction and suction looping. In other words there should be two sets of temps: two pipes too hot to touch and two about ambient. But I did not see that. I plan to strap some temp sensors to it to get better readings. Could a bad reversing valve cause what we are seeing? FYI the reversing valve is only energized in cooling mode. Energizing might hold it in place whereas at rest it maybe free to flop about if worn out.

In relation to that I am still wondering about my outdoor coil's TXV. If it is bad and closing most of the way, could it cause back pressure all the way back through the indoor cool, and back to the reversing valve causing it to open? Remember I have no TXV inside, so it should be a straight shot, albeit a long one.

Thanks for all your help.