M7040 Expansion Valve Replacement

[Jim L.]

Did the new compressor come with oil already filled?

PAG oil is what your machine uses. A little on the o-rings helps to seal them.

The M7040 shows a charge of 2 pounds (32 ounce) of R134a. If you use a small scale to measure the refrigerant in, you will be almost perfect in getting the charge right. Vapor charge the low side with the can(s) right-side up.

At 86 degree F, Lo side should be 21-28 psi; high side 185-242 psi. At 100 degree F the HI side may go up another 45 psi.

In this heat maybe it's time to switch to ice-cold beer.

 

[beefmaster]

Affirmative on all, just worried about system "filling up" so fast and compressor not turning on. calling ac guy to see if he's coming over this pm. paid forward with whiskey, cold beer coming as temps get over 100!

 

[beefmaster]

may have identified problem. When I took out the evaporator a wire fell out. Looking at it, it's a probe that fits in the fins of the evap, called a "heat sensing tube" in the shop manual and a "thermistor" in the parts manual, it unplugs from a harness that goes to the expansion valve.

since if fell out, I reinserted it when I put the evaporator back in - but, it apparently hung on something and the metal prong (the other one is plastic) broke off, thus disabling the evaporator. new one ordered (no photo) hope it works and solves problem.

 

[Jim L.]

It's a "frost thermistor" and the resistance varies with temperature.

It drives the thermo amplifier; which has a pressure switch going through the amplifier; and next in series is the compressor relay.

If the refrigerant is low, the evaporator temperature can fall from about 40 degree F to 32 which causes the evap to freeze up and blocks the air flow.

 

[beefmaster]

so if probe were broken, compressor wouldn't start?

 

[Jim L.]

Assuming that it is a negative thermistor, cold would raise the resistance. No thermistor means high resistance which translates to cold temperature and freezing or below on the evap coils. Thermo amp does not conduct and the compressor relay is shut off.

 

[beefmaster]

A/C fixed! blowing really cold air, expansion valve must have been issue. thanks all.