I’ve got a 2000 Mazda Protege. Up until about a month ago, the AC worked great. Then, summer hit and now the AC kind of comes and goes. It usually stays on in the morning, at least for an hour or so. Then the fan starts blowing hot air. The AC will sometimes come back on after the engine has been off a while, but sometimes it won’t come back until the next morning.
I took it to the mechanic, who says the freon levels are strong. He performed some tests and found that when the AC starts blowing hot, the compressor is actually drawing a vacuum. He thinks it might be a bad expansion valve, but he’s not sure. He thinks he might have to replace the entire AC system, which would probably cost more than the car is worth.
I’m willing to replace the expansion valve if that will fix the problem, but I don’t want to pay $500 and still have a bad AC unit. Does anyone have an idea about what’s the real problem here?
I had a similar problem with a Ford Aerostar van. It turned out that the thermostatic coupling with the mechanical fan didn’t allow the fan to move it full speed. The mechanic found it by hooking up his gauges and found that the pressures really went up when the air conditioning quit pumping cool air. He then took his big shop fan, directed the air through the grille. The pressures dropped and the air conditioning came back.
Now, your car probably has an electric fan. However, if there isn’t enough air flow through the evaporator to remove the heat, the air conditioning won’t function properly.
If the low side is going to vacuum with the system fully charged there is a restriction in the system somewhere and the expansion valve is the most likely location and desicant from the drier is a likely cause for the restriction. The mechanic may be concerned that desicant is scattered throughout the system and if the valve is replaced the compressor will soon fail and appear to be the result of his poor work.
@Rod Knox: If that’s the case, is there a way to squeeze a little more life out of the compressor by somehow periodically clearing the restriction/unblocking the valve? Any ideas on how this might be done?
I would replace the expansion valve and the drier and back flush the liquid line, then hope for the best. Continuing to operate the AC when the stoppage occurs will damage the compressor SOONER or later.
Also, @allsburg, if the mechanic is exaggerating when he describes the low side in vacuum when actually the low side is falling below 20psi while the high side is also comparatively low the problem may be the evaporator icing up. A restriction would cause the low side to approach or enter vacuum while the high side would likely be running well beyond 300 psi. Is the mechanic an AC specialist?
@Rod : Thanks for the advice. I’ll check with my mechanic on all the above possibilities.
Check the orifice tube for clogging.
Orifice tube ~expansion valve… FWIW.