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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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[–] indomara 4 points 3 months ago (1 children)

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."

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

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.

[–] jam12705 2 points 3 months ago (1 children)

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.

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

I’ll do another test today, but the fan is on lat time I checked. Any way to check how engaged the clutch is? When I spin it after turning off the car is doesn’t spin freely but how can I tell if the clutch is locking up as much as it should?

[–] jam12705 2 points 3 months ago (1 children)

The clutch is magnetic and you should hear it click when actuvated.

Another thing to look at is your temperature gauge, if your close to overheating the computer will shut the AC compressor off first to save on load.

Outside of checking the air flow and overheating the last thing I would check is the refrigerant charge. Have someone put gauges on and test the pressures.

[–] venusaur 1 points 3 months ago* (last edited 3 months ago)

Thanks!

Hm idk if I hear the clutch engaging but it definitely is. I can hear a loud motor type of sound when it’s engaged. Just don’t know how much it is engaged tho. Is this something that wears out?

It’s never overheating when it happens. Temp is good.

Charged the freon last year with a pump and gauges. Should be good but maybe there’s a leak. If there’s a leak would it work while driving but not while stopped for some time?