Colman heat pump sub cooling or super heat

pnichols wrote:

mark-45 wrote:
Hello, I have a colman-mach heat pump with 2 compressors in it. I had to change the one compressor and reversing valve on it. Does anyone know the proper sub cooling or super heat calculations for this unit?

That unit was on an RV???

Basement model RV AC units have 2 compressors (makes the equivalent of 2 roof top AC units). You have the option of running 1 or both compressors. Doug

mark-45 wrote:
Hello, I have a colman-mach heat pump with 2 compressors in it. I had to change the one compressor and reversing valve on it. Does anyone know the proper sub cooling or super heat calculations for this unit?

That unit was on an RV???

The accepted method is to charge by weight on these units.

mark-45 wrote:
Hello, I have a colman-mach heat pump with 2 compressors in it. I had to change the one compressor and reversing valve on it. Does anyone know the proper sub cooling or super heat calculations for this unit?

RV AC units do not require what Home systems require. ON the spec plate of your Coleman, you will see the EXACT Ozs of Freon 22. You install THAT amount and the system is correctly charged. You MUST have a AC dial a charge to do the work. Copy and paste see what one looks like. Doug

http://shop.advanceautoparts.com/p/robinair-r-134a-model-dial-a-charge-refrigerant-gauge-rob34205a/17631180-P

Moved from Forum Technical Support

No matter what brand, size or refrigerant I watch the whole picture as I charge. Older units with beat up or corroded coils can't take a lot of sub cooling without pushing the head psi too high. FWIW, Cap tubes are a crude device, those tiny filter driers are usually poor quality and the mfgrs often don't do a good evacuation so there's a good chance of improving the cooling on even a new AC by redoing them right. Sub cooling is paramount for increasing net refrigeration effect (NRE) as long as everything else looks good. I've installed a split system w/txv that would handle 17 degrees SC and T sat was only 20 degrees over ambient. With a cap tube, you're also limited by superheat. Say the SH is down to 10 degrees and the SC is only 1 degrees or so.... You're stuck with that. Or if the SC is only 1 degree or so and the T sat is sky high, like 30 over ambient and SH is still too high... You've got a big problem. Sorry if you already know all this stuff but this is what makes it so interesting and fun! So anyway, I'm happy if I can get only 5 degrees SC or even less, if T sat is around 20 over ambient and SH is down to 10 or so. That's for high SEER units and a clean coil. You have to adjust for the equipment condition and efficiency. Get the SH down to 10-12 and watch the head psi and hopefully you'll have a few degrees or more SC and T sat that's good... 20 or a little more, over ambient. But... If the SH is down to 10-12 and you don't have much, or no SC and T sat is good, that's also fine for a cap tube. You can't count on SC with a cap tube and that's why a liquid line sight glass ahead of a cap tube is worthless. Good luck! Craig