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on hot humid days a/c doesnt blow cold until vehicle is moving

louiel1 on Thu July 30, 2015 2:17 PM User is offline

Year: 2001
Make: chevy
Model: silverado
Engine Size: 5.3L
Refrigerant Type: 134

On hot humid days a/c doesn't blow cold until vehicle is moving, and sometimes it will go warm and smell "musty" when in slow traffic. Just had system professionally checked and recharged, I was told it was alittle low, but tech said that it wasn't enough to cause a problem, he also said the high and low switches were working properly but it is still doing it. Any ideas?

Cussboy on Thu July 30, 2015 2:49 PM User is offline

Hmm "until vehicle is moving"...that sounds like an issue with air flow over the condenser. Has the fan clutch been changed? Or, if electric fan(s) are they all spinning full time when the AC is on?

See, when the vehicle is moving, a ram effect keeps that condenser cooled enough to change the hot gaseous refrigerant to a hot liquid. I'll assume all such fan shrouds are intact and how they should be, and that the front of the condenser isn't blocked by debris...

louiel1 on Thu July 30, 2015 4:07 PM User is offline

I have a clutch fan with 60,000 or 280,00 miles on it, the engine was changed at 214,000 and I'm not sure if the fan was changed at that time, I know the belts were
all shrouds are in place, cond. is clean. At a temp of 88 the fan will move with little force and rotate about 1/8 of a turn before it stops

Edited: Thu July 30, 2015 at 4:15 PM by louiel1

mk378 on Thu July 30, 2015 4:46 PM User is offline

One test is to spray some water on the condenser, if performance improves suddenly it's likely an airflow problem.

Can you get pressure readings?

Also you should never see the high pressure switch act in normal operation. If the compressor is tripping off on high pressure it's either overcharged or a condenser problem.

Jag987 on Thu July 30, 2015 5:40 PM User is offline

When the engine is hot, like after a drive, open the hood then shut the engine off. If the fan make more than one revolution, there is a good chance it is not locking up like it should and is bad.

I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

louiel1 on Fri July 31, 2015 2:58 PM User is offline

I tried the fan test , it stopped dead, no overrun. I will carry a spray bottle and try the water next time the air goes hot
I am surprised at all the reply's, thanks for helping a backyard mech.

bohica2xo on Sat August 01, 2015 12:49 AM User is offline

Fan clutches cause problems long before you see overheating. Higher underhood temps are hard on electronics and plastic.

Here is the testing process:

Testing fan clutches


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Cussboy on Sat August 01, 2015 9:29 AM User is offline

Originally posted by: bohica2xo
Here in Las Vegas, I see it all the time - the vehicle does not boil the radiator, so the ASSumption is that the clutch is OK.

Just because a vehicle does not overheat, does not mean that the fan clutch is operating correctly.

Here in Phoenix, I've generally gotten about 6 years out of fan clutches. My 1988 B2200 has a Hayden lifetime warranty one, and I've replaced that a few times in the 21 years I've had the truck, and none of those times was because of the engine running hot, but because the AC performance/condenser cooling dropped off.

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