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Sparkybuoy
Sparkybuoy, Auto Mechanic
Category: Car
Satisfied Customers: 639
Experience:  20 years experience
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2000 gmc: z71..air conditioning blows cold..blows warm air

Resolved Question:

i have a 2000 gmc z71. The air conditioning blows cold when the truck is at idle, once the truck is moving the system intermittingly blows warm air, the only way to stop it is to shut the switch off, wait a couple of minutes and turn the switch back on. Some times this works and other times not.
I have replaced the switch on the accumulator and it changed nothing. I suspect the problem is electrical. Can anyone help?

Thank you
Submitted: 10 years ago.
Category: Car
Expert:  Sparkybuoy replied 10 years ago.
You need to speed up the engine with the hood open and the A/C on Max and high blower and watch the A/C clutch...is it staying engaged at idle but not at higher speed? Cycling on and off frequently? Sounds like low refrigerant. If it stays engaged while revving it to about 2000-2500 rpm and cycles every 10-15 seconds, then check the fan clutch for not locking up and not drawing enough air thru the radiator/condenser. If it doesn't cycle off at all, even after holding it at that rpm range for 30-60 seconds, then it's overcharged.
Customer: replied 10 years ago.
Reply to Sparkybuoy's Post: the a/c will run continually at all fans speeds when at idle. When you start driving, the unit works fine at all speeds for a quite a while. Yesterday it took 1 hour plus on the highway before it malfunctioned. Once it quits cooling, the only way to get the air to come back on is to shut the fan off, wait a minute or two, and turn the fan switch back on. This will allow the unit to start cooling but it only lasts for a few minutes and you must go through the same steps again
Expert:  Sparkybuoy replied 10 years ago.
So what you're saying it's a problem with the airflow out of the vents stopping...or is it the compressor that cycles off and won't re-engage?
Customer: replied 10 years ago.
Reply to Sparkybuoy's Post: the airflow out of the vents changes from cold to slightly warm air, once you turn off the switch and wait a few minutes and turn the switch back on, cold air will continue for a couple of minutes and then warm air starts again. It seems that on smooth roads the problem does not occur as much as on rough roads
Expert:  Sparkybuoy replied 10 years ago.
All you're doing is shutting the system off and that also shuts the compressor off and equalizes the system until you turn it on again and it starts cycling on and off frequently again. If you go under the hood and rev it up to about 2000 rpm with the A/C on max/high blower, if it's not too low on refrigerant, the compressor should stay on for 30 secopnds or more than cycle off when the evaporator gets cold enough to keep it from freezing over and then when the temperature rises again it will cycle the compressor back on again. Being that's it's a 2000, if it's never been serviced, it's probably time.
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