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2005 GMC Sierra, poor a/c performance

ncprog4 on Mon August 10, 2009 1:55 PM User is offline

Year: 2005
Make: GMC
Model: Sierra
Engine Size: 5.3
Refrigerant Type: 134a
Ambient Temp: 90-100
Pressure Low: 35-40
Pressure High: 230-250
Country of Origin: United States

I have the above crew cab pickup, it has the automatic climate control. I have had the truck since it was new. It has very low miles (25000) and has never had any a/c problems. But I checked the temp. of the air coming out of the vents (with the temperature turned all the way down (60 deg.) and on recirculate.) The air coming out of the vents only got down to about 47 degs. I thought maybe after 4 years it was a little low on freon. I added about 6 ounces but it didn't improve any so we purged, vacuumed, and put in the specified 1.6 lbs of freon. Now it would only do about 55 degs. at 1500 rpm. Low side pressure was about 42 lbs. We thought maybe our scale wasn't accurate, so we let some freon out. Still the best we could get was 47 degs. We continued letting freon out until the compressor started cycling. then we added just a little bit. So, through all this, the best we could get for the low pressure side was 35 lbs. and 47 degs. out of the vents.
Does it sound like we did anything wrong? Or is that as good as it gets?

GM Tech on Mon August 10, 2009 8:43 PM User is offline

47 on high fan is probably as good as it gets-- low forties, high thirties on low fan recirc would be good as well---they never were the greatest systems....

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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