97 Blazer. A/c blows hot air but the compressor is working and the dryer is ice cold. The hot/cold dial has no effect but I tested it with a meter and it is working (0-12.4 volts)

Please help!

 

Sounds like the blend door is sticking/stuck. Fairly common problem on these vehicles. There are a number of threads on here as to the cause and solution.

 

Couple months ago my AC was not working yet the compressor was fine as well. Turned out I had a cracked schrader valve on the AC port, replaced it, put some R-134a, and was all good again!

 

Could very well be the blend door, Christine is one of the resident experts on that issue.

Do you have a set of gauges to check the low and high side pressures. You could also have a restriction or low gas and a frozen evaporator coil.?

George

 

Thanks George. I'm flattered. Yes, the blend-door is an obvious culprit here. It is electronically controlled and the axle that engages the door can slip if the main gear through which it passes has cracked. You can replace it, depending on the year if you reach in through where the glove compartment is located.

Another thing to check is if there is a vacuum leak in the under-hood vacuum hoses. Vacuum supplied by the engine is used to operated the other HVAC valve actuators that direct the heat/cold to different parts of the HVAC system under the dash. This same vacuum supply also is responsible for the actuation of the front axle. It is well worth checking these hoses. Nice thing is that replacement of the hoses, at least on a 4-button transfer-case 4wd system, is pretty easy and not very expensive.

The hoses under the dash are made of better material but the ones in the engine compartment tend to rot by the time they get to being 15 y.o.

Note also that the blend door actuator is different depending on if you have a manual HVAC system or a Computer Controlled (you set the temperature) system.

In a pinch, you can check if the blend door is working by removing an access panel (on some Blazers) that allows you to look down onto it from the engine side of the fire wall. See the pictures below.

For information on the vacuum hoses, check my signature for a link on it.


Green is the the AC evaporator. Red is the access panel.


Red arrow shows the door. The axle shaft is in yellow. I forget which position this corresponds to. But it should move depending on the temperature setting.