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Bob, Auto Tech
Category: Chevy
Satisfied Customers: 4087
Experience:  Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)
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Blazer: 99..Chev..10 A/c just started blowing hot air

Customer Question

My '99 Chev Bazer S-10 A/c just started blowing hot air and occasionally cool air off and on. What do you think is wrong?
Submitted: 8 years ago.
Category: Chevy
Expert:  Bob replied 8 years ago.
This is going to take a process of elimination to find the reason for it. First thing you need to do is to verify if the AC is getting cold or not. When the AC is running feel the accumulator under the hood and see if it is cold. If the AC is not working, there won't be any cold air to blow into the truck. Look to see if the AC compressor clutch is engaged when the unit is turned on. Then if it is, let it run for a while and see if it stays engaged or if it cycles on and off. It should cycle once every few minutes, but if it cycles over and over rapidly, it may be low on freon. If it is low on freon, it will act as you describe. If on the other hand the system stays good and cold all of the time and cycles in a normal manner, chances are you have a problem with the HVAC case mode door inside of the truck. The door could be either broken or the actuator that makes it work could be bad. If you set down in the right front seat and listen below the glove box, you may hear the door or actuator going click, click, click or something similar. If it does not, move the hot and cold control from hot to cold and listen to see if you can hear the door shift modes. Also you should be able to feel a change in the volume of air flow. If that is not happening, you may need to remove the glove box to see if you can visually see the mode door actuator. If so, again move the control and note if the actuator linkage moves or not. If the linkage moves but the temp stays the same the problem is inside of the heater case. If it does not move, then either the actuator is bad or the control panel where you select hot and cold. Then check to see if the voltage going into the actuator changes when you change the control lever. If it does and the actuator does not move the actuator is bad. If the voltage never changes, you have a problem in the control panel or wiring. To replace the actuator, you may need to roll the whole dash panel back or even remove it. Let me know what you find and we will go from there. Thanks
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Customer: replied 8 years ago.
I think it's the Freon because it keeps clicking on and off every few seconds.
I'll use your guide to go over the symptoms with my mechanic.
Thanks for the diagnosis.
Tom Bolton
Expert:  Bob replied 8 years ago.
If it is clicking on and off a lot, you are probabley correct. Low freon causes that. There is a good chance you may have a leak. If they ad freon, have them also install a leak detector fluid with the feon and do a sniff test on it for leaks, too. Good luck and thanks for the accept.
Customer: replied 8 years ago.
Already replied.
Expert:  Bob replied 8 years ago.
You are welcome.
Customer: replied 8 years ago.
I already accepted and paid.
FYI It was the actuator under the dash that they say is stuck open so heat is coming in.
My mechanic told me that it would cost about $800 including the part because they would have to remove the dash to fix.
Good thing it's almost winter.
Think I will ride around with the windows down until then.
Expert:  Bob replied 8 years ago.
Hi Tom, Thanks for the update. Glad you at least now know what the problem is for sure. Hate to say it but the price they quoted does not sound out of line at all. It is a really big job as they do have to remove the dash pad in order to get to the heater case and replace the actuator. You may also want to toy with the idea of installing an old fashioned hot water shut off valve in the heater hose as an optional way of shutting off the hot water supply. Not original but could be made to work cheap. Just a vacuum operated valve like we had on the old Chevys and a switch to apply and take away vacuum from it. There are still some out there that work off of a cable too, just a thought. Thanks
Customer: replied 8 years ago.
I know the price is fair, just comes at the wrong time.
That's a great tip about the shut-off valve.
I will do exactly that at least until it starts getting colder.
Thanks and I will sure be talking to you again.
Tom Bolton
Expert:  Bob replied 8 years ago.
Your sure welcome, Tom. Thanks again for the accept and for using JA. If you need me again and ever post a new question, just put my name in the subject line and I will be notified. Thanks

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