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Think it through VERY carefully.

Many years ago I was replacing a compressor and I had the system charge isolated in the indoor coil between the reversing valve of the heat pump and the liquid line valve. So far so good. This is before EPA.

The GE reversing valve was in the deenergized heat position and had to be energized (O terminal) to switch to cool. The system was open and I heard a click and a big WOOSH as 18# of R22 made an exit out of the open 1 1/8" suction line. The customer may have activated the cooling cycle at the stat. I had failed to consider that possibility. I was lucky only to be startled.

The way I used to always do it on the units with semi-hermetic Copeland recips is remove the liquid line solenoid coil from the valve and manually open the solenoid valve with a magnet. Then I'd close the liquid line service valve, and run the unit through a normal pumpdown cycle with a gauge connected and the low-press. switch temporarily jumped out. You can terminate the pumpdown around 5 psig using the control stop switch for that circuit. Transfer the leftover refrigerant to the condenser.

For the units with scroll compressors, the procedure is the same, except you pump them down to 20 psig.

Don't have the model # offhand but it uses microtech controller

Most of the current RPS' pump themselves down at the end of the cooling cycle.

You're on the right track. Let the unit pump down, and then close the service valve near the filter. You'll still have some refrigerant in the evap to pull out, but it shouldn't be too much. Then you can change filter, and put everything back.

What is the model # and what controller is in it?

Mcquay RPS

Hello I have to change filter driers on a mcquay rooftop package unit, can I pump down, de energize the solenoid, close that valve at the corner, and hope the solenoid don't leak, I'll recover if I have to but is there an easier way, I'm still learning these big units, thanks.