Pressure Ramping Up

[Joedoitall]

I have a Split system 3 Ton Heat Pump, R22, 13 Seer, Fixed Orifice, Nordyne Mfg... About a week ago the unit seemed to struggle to keep the house below 80 degrees. To bring the unit within the manufactures parameters, (i.e.15 deg super heat), I had to add just over 6 lbs of *****. I proceeded to check for leaks with 1st a halogen leak detector & then with a Spectroline UV injection die, but no leaks showed up, instead now I notice in cool mode the Suction Line at the entrance to the evaporator is ice cold within the first 5 minutes of the on cycle. So with the unit off I put my gauges on with the Condenser & turned power back on, normally the pressures would stabilize at about (Suction: 75psi & Liq: 200psi within about 5 minutes). However both the Suction & Liquid Pressures dropped super low; (Suction 20 psi Liq: 135 psi). I would have suspected there is still a leak, however within 20 minutes the pressures stabilized back to normal. I let the unit cycle off & back on normally but each time the pressures take about 20 minutes to ramp back up or stabilize to normal. The reversing valve & condenser heat pump by-pass valve energize properly on cool mode with consistent temperatures across them, indicating they are within operational parameters. I suspect the compressor which is 9 yrs old is losing pumping efficiency.. I am a Industrial Engineer and very familiar with most HVAC principles and have worked on Straight cool residential split systems over the 12 years, but not many heat pumps. What are your thoughts or experiences on this?

[Magoo]

Hi
the principals remain the same if industrial or heat pumps, I would be looking at the reversing valve as a start point, they do wear out in the slide piston and bypass/ leak and then float around. Check with an IR thermo or clamp thermocouple.

[monkey spanners]

Would expect a comp thats not pumping well to exhibit a low high side pressure and a higher than normal low side pressure.

Not sure where abouts on the system you are taking the pressures, true suction, and discharge or by the sservice valves, but sounds like there is a restriction or as Magoo says a problem with the rv.

Does it run ok in heating?