this post was submitted on 23 Aug 2024
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Diagnosing A/C Failure When Idling (self.mechanicadvice)
submitted 3 months ago* (last edited 3 months ago) by venusaur to c/mechanicadvice
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2001 QX4

It has been 90+ degrees where I live and when idling for more than 10-15 min, the A/C stops blowing cold and is humid. Works great otherwise when ambient temps are low and car is moving. The Freon pressure is good. The Enser is old and has some dents, but has been cleaned and looks to be getting airflow. How can I tell what is wrong? Replace the radiator fan clutch? Condenser? Something else? Should also note that the engine temp gets high when on long stretches up uphill highway, but I think that is somewhat normal for an old car, no? Thanks!

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[–] [email protected] 2 points 3 months ago* (last edited 3 months ago) (1 children)

Not an HVAC pro but these are a couple of things I can think of,

  1. check to see if the compressor pump is turning when it stops cooing, might be an issue with the electric clutch on the compressor. also check the voltage at the clutch if it stops engaging to see if it’s the clutch or something else causing it to stop
  2. to much coolant line, is it over pressure? have you been filing the R134 yourself from small cans? it could be “icing up” due to to high of a head pressure at the compressor. check the pressures both at the high side and low side with a gauge set
  3. blocked drain line, the coil in the car will condense water that drips down and out of the car with the drain line blocked drain could cause it to ice up
  4. blocked/low air flow will also cause it to ice up make sue that both the evaporator and condenser coil are free of junk, a layer of dust can often form lowering the airflow past the coil causing it to ice up, you might need a inspection camera to look at the coil inside the car without taking the dash apart
[–] venusaur 1 points 3 months ago* (last edited 3 months ago) (1 children)

Thanks for all the tips. Time to do some detective work.

  1. I’ll check if the compressor is spinning next time.
  2. i flushed and refilled the freon last year and made sure it was balanced on both sides based on the ambient temp using a gauge set. I could check again. How could I tell if it’s icing up?
  3. I see a puddle under the car when parked after A/C has been on, but I’ll check to see if it’s blocked.
  4. Condenser is as clean as I can get it. I’ll have to open the dash/glove to check the evap coil. Maybe a camera would work.
[–] [email protected] 3 points 3 months ago* (last edited 3 months ago) (1 children)

When you flushed and replaced the coolant did you draw the lines down with a vacuum pump before filling with new oil/coolent? If it got moisture in the line it might have caused junk to form in the metering tubes? You can use an inspection camera to see if there is frost covering and blocking the airflow through the evap coil

Also as @jk43 said check the schematic and see it there is a high temp thermostat on the compressor, might just be a bad thermal switch or something wrong with the compressor

[–] venusaur 1 points 3 months ago (1 children)

Yeah I used a pump. That reminds me. I think there might have been a leak because it wasn’t holding zero pressure. If that’s the case then moisture could be getting in, but wouldn’t that cause the system to not function properly all the time?

[–] [email protected] 2 points 3 months ago (1 children)

depends on how much is in it.

[–] venusaur 1 points 3 months ago (1 children)

Do you know what the next steps would be to find and fix the leak? Dye? Leak detector device?

[–] [email protected] 3 points 3 months ago (1 children)

leak sniffer, last time I needed one I rented it from the auto parts store that had tool rental, it was like $5 but I had to leave A big deposit until I returned it.

[–] venusaur 1 points 3 months ago

Cool. I did that with the pump and gauge set. I’ll try it. Thanks!