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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.
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