Automotive Air Conditioning Information Forum

Hello everyone, I`m having some weird ac problems, so what is happening is that sometimes the A/C freezes up, sometimes works perfect for days and sometimes would blow slightly cold air, low side would be on 30 psi high side on 150 psi, when it freezes up low side would go to 0 psi and high side would be on 150 psi, parts I have already replaced would be the dryer and expansions valve, vacuum for 1 hour and re-charge to spec which is 500 grams, I also check the evap temp sensor and its working, the clutch would disengage at 3.5v, when it freezes it stays at 3.3v, but if i turn the blend door to the middle between hot and cold and it blocks off the evap, the temp sensor goes up to 3.5v and the compressor disengage, then cycles as usual, only thing that I have notice is the compressor is making a knocking noise and when I turn the clutch part of the compressor by hand, 1/2 turn has resistance( compressor compressing the r134a), and the other 1/2 turn it spinnings freely then gets back resistance then it repeats, could it be that the compressor is weak and not cooling enough to bring the temp sensor to 3.5v causing it to stay on and freeze up?, any advice ?

Need make/model/year
Is this an R 134 vehicle
was any work done on the AC system just prior to symptoms occurring

Only the expansion valve and dryer was change looking to solve the problem, its a 2005 Mitsubishi lancer, r134a, all fans are working only thing we did was clean the evap because it was dirty from in the cabin. the system wasn`t opened, if you rev the engine( stand still) the a/c gets a little colder

I have my doubts about the comp, but want to see what another consultant has to say. Wait for JohnHere to reply

OK thanks because I`m at a lost, freezing up is due to moisture, expansion valve or a bad evap temp sensor, I don`t know if a weak compressor can cause it to freeze up if its running for too long and not cycling the system only has a high pressure switch and a temp sensor, when we changed the expansion valve, we blow through the evap and it didn`t feel restricted, want we blow in came out the next side, same for the condenser, but it felt a little restricted, we think its because of the fines being so small, but if a condenser is restricted it would cause the high side to be low because the service port for the high side is after the condenser and the line would feel cold or much cooler than normal

I believe that your car has an electric (electronic) control valve mounted in the compressor that could be malfunctioning. I would try replacing it as they're relatively inexpensive, although you'll have to recover the charge, complete the replacement, evacuate, and recharge the system.

Check with the Forum sponsor for the correct part.

I googled it, it's a Mitsubishi fixed scroll. The way you describe resistance turning it sounds like it's a good compressor, that's how scrolls feel.

Sounds kinda like the temp sensor might be dislodged, i.e. working but not in the correct position.

The evaporator doesn't get blocked off by temperature blend doors, air always runs through the full evaporator.

I have no idea what your hvac module looks like, sometimes you can pull out the evaporator freeze thermistor wire and peek in there with a borescope, sometimes you can just fish straight down a center panel register with hvac set to full cold, panel mode and see it. Your evap inlet might also be partially blocked, take out the blower motor/wheel and look with mirror or borescope

I went and felt a good compressor and it doesn`t have the 1/2 turn free wheel spin, it has resistance for its full turn, I left the blend door slightly off cold and it hasn`t freezed up since, the compressor cycles, its like the blend door slightly close pushes some of the cold air back on the sensor and cause it to cycle once i put it on fully cold the compressor runs constantly, and the A/C feels cold ish, if i rev the engine at stand a still the A/C gets cold and it starts to cycle

DetroitAC wrote: ↑Mon May 16, 2022 4:25 pm I googled it, it's a Mitsubishi fixed scroll. The way you describe resistance turning it sounds like it's a good compressor, that's how scrolls feel.

Sounds kinda like the temp sensor might be dislodged, i.e. working but not in the correct position.

The evaporator doesn't get blocked off by temperature blend doors, air always runs through the full evaporator.

I have no idea what your hvac module looks like, sometimes you can pull out the evaporator freeze thermistor wire and peek in there with a borescope, sometimes you can just fish straight down a center panel register with hvac set to full cold, panel mode and see it. Your evap inlet might also be partially blocked, take out the blower motor/wheel and look with mirror or borescope

I checked its clipped into the evaporator, it was never touched