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Very high pressures??

mrbear3800 on Sat July 19, 2008 8:01 PM User is offline

Year: 1999
Make: Chevy
Model: Blazer
Engine Size: 4.3
Refrigerant Type: R-134a
Ambient Temp: 75-80
Pressure Low: 55
Pressure High: 325+
Country of Origin: United States

Hello again. Recently, this site was very helpful in helping me diagnose my car's A/C (95 Grand Marquis).

My friend has a 1999 Blazer with marginal cooling. His father just wanted to dump some refrigerant into it but I told him to at least bring it over so I could check his pressures first. So I checked the vent temps, which were about 60F in NORM, 45-50 on MAX(75-80F and humid). He said if it is driven around for a bit, it gets decently cool.

Then we checked the pressures: 55-60 low side, over 300 highside and climbing. It got as high as 325+. Clutch never cycled off once, even when I raised the RPM's. The Accumulator/drier was nice and sweaty during this. The compressor sounded a bit on the noisy side.

I then sprayed some water on the face of the condensor and the highside dropped down to 200. But vent temps didn't drop and the compressor still didn't cycle. Whats going on here? Is it a condensor airflow issue? Are those pressures way too high for this vehicle?

Thanks!

Edited: Sat July 19, 2008 at 8:03 PM by mrbear3800

Chick on Sat July 19, 2008 8:20 PM User is offlineView users profile

I would recover the charge in case someone added refrigerant, unless you know for a fact no one ever did, and people do hold back that information.. then I would change the fan clutch, it is not doing the job as the water test shows..Hope this helps..
PS: if someone added refrigerant, could be air in the system, or some sealers etc.. Pull the O tube when you evacuate it, the low side indicates bad or worn reed valves if no air is in the system. Hope this helps..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

mrbear3800 on Sat July 19, 2008 10:03 PM User is offline

Ok. I shall relay that info, thanks. But they're cheap and probably won't want to take it to a shop. I already told them at the very least to pull the radiator and clean that and the condensor out. Helped with my car at least. The fan seems to be moving a lot of air but it appears to be original and the truck has 105K miles on it.

Also, is there a general pressure chart for auto a/c systems or would the pressures be different for different cars/manufacturers?

Thanks!

Edited: Sat July 19, 2008 at 10:04 PM by mrbear3800

Chick on Sat July 19, 2008 10:27 PM User is offlineView users profile

There isn't a "general" pressure to go by, especially with mechanical fans..Electric fans "usually" run around 2.2 to 2.5 times ambient temp with a factory system (non retrofitted) but with engine driven fans, to much depends on the condition of the fan, thus the water mist test... So the upper end of 2.5 would be as general as you can go..Those miles would indicate a new fan clutch to me..Just my opinion...Hope this helps..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

mrbear3800 on Sat July 19, 2008 10:40 PM User is offline

That's good to know. Looks like 300+ is a bit on the high side then, lol. I should have also noted the static pressure was 75/75 and the compressor noises I mentioned was a knocking type noise (i saw a reference to that while searching other Blazer posts). It wasn't real loud but definetly there.

Chick on Sat July 19, 2008 10:49 PM User is offlineView users profile

At 80 degrees, 300+ is high, no doubt about it...Have them at least change the fan clutch, clean the condenser and area between it and the radiator..You need good air flow thru them..hope this helps..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

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