16yr old central A/C. High side=200psig, low side=80psig. Only seeing about 12 degree drop in inlet/outlet?l?

Question

Inlet Temp = 76.0F, Outlet = 64.0F. Outside ambient = 76 and rainy at the moment. I don't get it. How do I get a 20 degree drop? I want to try to do it myself before calling a professional.

The evap coil is not frozen, and when I dropped the low side down to 68psig (38F), it didn't seem to work any better, with about the same degree difference and a high side of only 190 or so (taken same night as recharge). Yes, R-22 system. There was more "sweat" on condensate drain pipe with 80psig lowside than 68psig. So I assumed the coil was colder. Apart from cracking open the ductwork, I don't know. The evap coild could very well be dirty. Things just don't add up.

Condenser coil and unit is clean...washed out with high pressure water. Fins are in GREAT shape...no bends or damage.

Here's a another part to my question. Lowside pressure is taken at the unit, right next to high side pressure. If the evap coil is about 25 feet into the house, does the reading for lowside pressure still apply? I read that pressures are different throughout the system...so would a 68psig reading at the unit indicate a 68psig pressure at the evap coil...thus a 40 degree F coil? THANKS GUYS...

Answer 1

I'm assuming you AC is using R-22 as a refrigerant. the low side pressure reading indicates an over charge, (the higher the pressure - the higher the temperature) If you look at the R-22 scale on the low pressure gage 80 lbs of pressure puts the temp in the range you've stated. It's an old unit, and it may be designed to be less efficient than a newer model. Your high pressure reading should be the ambient temp + 150 - 165, in your case 76 + 150 = 226. If it's raining the cool rain water will drastically reduce the high pressure. It's no different than spraying water on the condensing coil. It's normal to have a low head pressure reading if cool water is falling on the condenser.

As mentioned previously, you might need to check your air filter and A-coil to see if it's dirty. Dust and lint act as insulation and restricts the air flow.

Answer 2

Sounds like you have bad compressor valves. Assuming the charge was correct, all indications are that. An 80 degree suction adds up to the 12 degree delta T on the coil. You probably have a high superheat also. When you reduced the charge, you made it worse, even though you thought you had a 40 degree coil.
A dirty evaporator would make the suction low, not high! If the evap was dirty and you clean it, the suction will go up even more. If the unit has service valves, try pumping the unit down to see how far the compressor will pump down. It should go into a vacuum if valves are good and lineset is short. Check compressor amp draw too. If low compared to the nameplate RLA, it is bad valves.
High suction+high superheat+low temp. drop on evap+low amps=bad suction valves

Answer 3

take analog or digitel probe style therm and ancheck your temp about 3inches above acoil then ckeck temp at inlet vent then minus inlet temp from acoil if you pull18 to 20 differance everythings probably fine if your below 18 ya might need to clean acoil and out side unit coil

Answer 4

You would have to run a full service on this unit, including but not limited to a recharge...Call a professional, they have all of the equipment necessary to do this, and it is usually cheaper then buying all of the tools necessary to do it yourself.

Answer 5

did you check to see if it froze up? could happen in hi humidity. turn off and let defrost for a few hours