I've been having problems with the AC on my wifes blazer, me along with a few friends have looked at it and tested about everything we know, here's quick rundown of what it doing

2001 blazer

When is 90 or above out the ac won't work at all

when its below 90 the ac will work on the highway most of the time, last night it shut off a few times on the highway

95% of the time while driving it town it doesn't work

When the ac does work it blows cold like it should, then out of the blue the ac light on the dash will shut off, i press the light and it just blinks

The cycling switch is working correctly, but when the ac light shuts off inside the car, the switch loses power, but has power when it comes back on

Gauge readings are good, and is full of freion

I've had it at a couple of shops and when i go in and explain what the problem is, and what all i have checked already, they turn me away and say i've never heard of a problem like that we can't help you here

My guess is the Body Control Module is shorting out causing the ac controller to loose power??????

If there's anyone that can help me out, or if you know someone, i would appreciate it...thanks Justin

 

Sounds like the system is overcharged. High temperature and/or inadequate cooling will cause the high pressure cutout switch to open, disengaging the compressor clutch. If the high pressure cutout switch was opening up prematurely, it could cause these symptoms on a properly charged system.

The system has to be evacuated to replace the high pressure switch.

 

where's a good place to find a wiring diagram for the ac system, is there a way to test the high pressure switch before i take it off to see if its working correctly???...i've triple checked the sysyem and it is not overcharged...Have you ever seen a fan bad fan clutch cause this problem???...thanks for your help...Justin

 

A search for "hvac+wiring+diagram" (or some variant of that) should turn up some results. The basics of it won't be too much different from '98 thru '04. And I believe the high pressure switch functions the same in both auto & manual climate control systems.

The high pressure switch should read continuous with a multimeter set to test continuity. If, during operation, the switch opens up and the pressure on the high side is within spec, then the switch is likely bad.

When you have been checking the system pressures, what were the high side pressures while the clutch was engaged? The high pressure switch should remain closed unless the pressure exceeds ~300psi.

 

A bad fan clutch will not affect the AC while going down the highway. At 35 MPH the ram air is suffiecient to cool the AC and truck.

If you clutch fan is bad, the truck would also be over heating during city type low speed driving.

I agree with swartlkk, it sounds over charged. You stated the system is full of refrigerant. Please define full. Do you know if the charge was weighed in?

I googled "blazer ac flashing ac light" and found a few things. Is you system the automatic fancy dancy computer controlled automatic AC? Seems there may be a thermister that could have failed. They also talked about pulling codes out of the HVAC panel.

Good luck.

 

Swattlkk....the pressure on the high side was around 200 if i remember right

Kristoph30....no the charge wasn't weighed in...and it does have one of those expensive controller's in which i have already replaced

 

Kristoph30 you are the man..that thermister was the problem
the past 2 yrs of not having AC is finally over, all over a $19 part

Blazerforum.com ftw

 

Glad you found the issue. Could you give some more detail into what part you replaced, where it was, any part numbers, etc...Any additional information that may help someone else in the future while the info is still fresh in your head?

 

Glad you found it!

 

Swartlkk here's what i found on google with Kristoph30's suggestion

Its called the Ambient Air Temperture Sensor, bought it from GM for $19 today...its located behind the grill on the passenger side of the vehicle, was very easy to replace, just removed the clips that held the grill in, unpluged the old sensor and plugged the new one in, hooked the battery back up and it was good to go...it was above 90 degrees here in kansas today, usually it would never work above 90...thanks again for all the great advice, my wife doesn't know what to think having ac again

Had the same A/C button light blinking three time with the Climate Control Computer on a 98 Blazer. Turned out the problem was the Ambient Air Temperture Sensor. It is a thermistor, located on the right hand side of the grill in front of the A/C condenser. With little hands, one can reach through the grill and remove it for testing.

The thermistor resistance varies with temperature. At 32 degrees F, the resistance should be near 16,330 ohms and at 104 degrees F, the resistance should be near 2,663 ohms. You will need a digital multimeter, VOM, or the like to test this litlte bugger. Anyone that plays with electrical equipment should have this basic piece of test gear.

My failed sensor was telling the climate control computer that it was 40 degrees below zero outside and A/C wasn't needed, just roll down the window. The A/C did work sometimes as long as the outside temperature remainded in the 70's.