1y ago

Diagnosing A/C Failure When Idling

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!

16 comments

Had an issue on my golf where I had the secondary radiator fan die, so it would de-rate the compressor and run the main fan full time. I put an after-market (cheap) fan in, but the system didnt think it was running and was causing similar issues where at speed it was fine but when stopped it wouldn't cool (compressor would run a few seconds then off for 30 seconds). It was not until I replaced it with a OEM 2nd hand that the system was able to see the fan running as normal, so the compressor was allowed to run as normal."
- Thanks! Unfortunately the QX4 only has one fan. I’ve seen that some people install an electric fan but I’d rather try to return it to working condition as Nissan intended, unless they didn’t intend to work in 100 degree weather.
  
  If the AC cooling while moving but not when sitting still you have an issue with airflow across the condenser. Check to ensure that the electirc radiator fan is actually coming on when idling and the AC is activated.
Not an HVAC pro but these are a couple of things I can think of,
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
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
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
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
- Thanks for all the tips. Time to do some detective work.
  I’ll check if the compressor is spinning next time.
  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?
  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.
  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.
  
  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
It might have a temperature cutoff for the compressor
- Ah so at a high temp the compressor stops. I’ll check to see if it stops spinning next time. That’s just normal function or is it possibly cutting off too soon because of something else. It has been really hot here but I would think that these cars would be made to handle up 90-100 degree weather.

16 comments