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runnin12s
runnin12s, ASE Master Technician
Category: Car
Satisfied Customers: 9
Experience:  Master Engine Builder / Degree in engines/electronics/steering/suspension etc.
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98 Chevy Blazer: S10..the air flow door..climate control..blow

Customer Question

I have a '98 Chevy Blazer S10 with 153000 miles. Before it became warm outside I noticed what I now think is the air flow door for the computerized climate control continually opening and closing. Now that it is warn out the air conditioner doesn't work and only very hot air will blow from the vents/floor. The selector for the vents and floor seem to be operating as they should. Both hoses for the heater are warm or hot. The air conditionser compressor is cycling on and off in short intervals. One of the lines on the compressor is cold and the other is warm which I think means the system is cooling but no cool air is getting to the inside of the vehicle. I have seen on other sites this same problem with other Blazer S-10s. Is this a common problem with an easy fix or rare problem with an expensive fix? Thanks, XXXXX XXXXX
Submitted: 11 years ago.
Category: Car
Expert:  runnin12s replied 11 years ago.
I have seen this a couple of times and it has usually resulted in a larger fix. First check for the vacuum lines going into the firewall from the engine. If you get lucky you will find a cracked or broken vacuum line running inside and therefore controlling the vacuum levers that select temperature. If this happens it could explain the doors opening and closing as the engine rocks and causes the vacuum to be lost to the controllers. if all vaccuum lines look ok go into the inside comparment and remove the glove box door. Inside you will see a clear plastic connector with several different color plastic vacuum lines coming out of them, you may have to remove some inner platic trim plates beneath the dash. inspect all of the lines running from the vacuum line in from the fire wall to the control unit itself and ultimately to the 2 different airflow valves "doors". if all vacuum lines appear to be in good shape go to the next step, start the vehicle and move the temperature control from full hot to full control (digitally from 90 down to 60 deg.) listen really close inside by the heater box (behind dash behind glove box). you should hear a vacuum sound and then a slight "thunk" as the vacuum opens and shuts the "thermal door". if the vacuum continues to hiss after the door actuates then you have a vacuum leak, recheck the lines for a break, if the vacuum hisses for a second then stops but you don't hear the "door" make the thunk sound then you have a vacuum solenoid problem. before determining this to be the problem I have seen a few instances where the retaining circlip that holds the vacuum solenoid onto the "door" comes off and the solenoid doesn't connect and therefore doesn't control the door. The reason I feel this is the best check is because if this door is not closing it would explain the hot air, the door blocks off the air from passing through the heater core (aka hot air) and redirects the air through the air conditioning portion of the heater box. hope this helps good luck

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