Well, yesterday was in the 80's so since AC season will soon be here, I did the usual spring maint. (wash out the condenser fins and change the filters) to the AC unit. I've got an antique (1973?) Coleman Polar Prince unit that is probably original to this trailer. Several years ago I paid a local company $80 to come out and add a pound of R-22 when my evaporator started icing up from low pressure but last summer things didn't seem as cool as they should be. Yes, I know that a new unit would be much more efficient but I only plan to live here for another year so I don't plan to go that direction.

Here's the question. While checking out the unit yesterday, I hung the gauges on it and fired it up and got the following readings with 80* ambient outside air temp.

35 PSI low side
190 PSI high side
78* air temp at the return register
61* air temp at the AC vent

Does this sound normal for a R22 system? It's been 15+ years since I did any HVAC so I need some help. Thanks in advance.

 

Nope, 35 psi on the low side is too low. Look at the gauges it will tell you on one of the inner rings the temp for 35 psi but it is way too low, about 12 degrees. or in other words it will freeze any condensate on it. Something in the neighbourhood of 65-70 is more like it.

Hope this helps.

http://www.longviewweb.com/pressure.htm

 

Yup, it's possibly low.

I imagine with the age of that system, plus it's in a mobile home, it's got "quick-Connects" in the refrigerant line-set. They're prone to leak.

While you're in the cleaning mode, consider the indoor coil. Check out the incoming air side and see if it's stopped up. That can cause BS readings on your gauges and lead one to think it's low on refrigerant. (The ultimate restriction of heat to the coil results in less refrigerant being boiled. That in turn presents with lower than expected pressures on both the low, and high side. As mentioned above, the lower pressures screw with the superheat and cause sections of the evaporator to run well below the freezing point of water. The frost/ice there block entirely the heat available to that section of the coil, making the balance run too cold, it pretty much snow-***** from there. The worst case scenario is you slug liquid refrigerant back to the compressor and bust its valves, seals, crankshaft, etc).

Consider soaking the coil with something like SimpleGreen or there abouts. In a perfect world, you could flush the coil forcefully with a garden hose. If you can't do that, squirt the coil in small places letting the water drain. It'll take a while, but well worth it in the long run.





But, . . . . . . right off, I too think it's low on refrigerant.