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Air blows cold and hot

fortee9er on Thu September 01, 2011 9:38 PM User is offline

Year: 1998
Make: GMC
Model: Safari
Engine Size: 4.3L
Refrigerant Type: R134a
Country of Origin: United States

The issue with my 1998 GMC Safari (with rear a/c) is that it will blow cold air when the engine is cold or when the engine is under load such as while accelerating. It will also blow cold air while cruising a 70+ MPH. When the engine is fully warmed up or while cruising at low speeds the air coming out of the registers is warm. Do I have a vacuum leak in the air distribution system? If so where should I start looking?
Thanks
Jorge

TRB on Fri September 02, 2011 12:28 AM User is offlineView users profile

It would be good to know the refrigerant level and pressure readings.

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Dougflas on Fri September 02, 2011 5:58 AM User is offline

If the airflow does not change positions ie: ifthe air stops coming from the dash vents and starts coming out of the defroster ducts, you have a vacuum problem. Your vacuum line is plastic and they do crack and break off.

GM Tech on Fri September 02, 2011 8:53 AM User is offline

"M" vans are also known for bad fan clutches - causing high pressure cut-outs

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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......

mk378 on Fri September 02, 2011 9:15 AM User is offline

Wait until it is blowing hot, then check under the hood. See if the compressor is engaged and the lines are cold.

fortee9er on Fri September 02, 2011 9:31 PM User is offline

The van's a/c system had a leaky schrader valve replaced, system vacuumed, and recharged (4.8oz of R134a) as called for by a factory sticker on the blower motor housing. The vacuum lines and vacuum reservoir in the engine compartment were replaced because the old ones had disintegrated and the air flow was directed to the defroster register on top of the dash.
After the repairs were made I noticed the problem with the cold/hot air situation. BTW the air volume remains the same regardless of the temperature.
How can I test the compressor clutch?
Thanks
Jorge

Cussboy on Sun September 04, 2011 9:57 AM User is offline

mk378 means to open up the hood and visually check that INSIDE of the compressor is spinning. If only the outside pulley is spinning and the inner circular portion is not, then the AC clutch is NOT engaged. Take a look first at the running engine with the AC off, then you'll know what it looks like; then switch AC on (when you say it's working) to see the difference.

Cussboy on Sun September 04, 2011 10:03 AM User is offline

mk378 means to open up the hood and visually check that INSIDE of the compressor is spinning. If only the outside pulley is spinning and the inner circular portion is not, then the AC clutch is NOT engaged. Take a look first at the running engine with the AC off, then you'll know what it looks like; then switch AC on (when you say it's working) to see the difference.

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