Hi! This is my first post. I appreciate in advance any advice you can give me.

The 4WD, heat and AC in my daughter's 96 Blazer all went out around the same time. This was right around the time that her boyfriend installed a new radio. I'm suspicious of the timing, all of those functions going out simultaneously. Is it possible that something behind the dash became disengaged or that wires were crossed back there when the radio was pulled out? The controls for the 4WD and the heater are all right above the radio in the dash.
We have had the heat looked at by a mechanic (flushed the heater core, checked vacuum) but I believe he only checked mechanical things, not electrical.
Basically, the heat and AC blow but not hot or cold.. just air.. and the 4WD does not engage (the light flashes when you try to go from 2WD to 4HI but then just goes back to 2WD. I don't believe you hear anything try to engage under the truck.) Oh, and there is a check engine light and it is pulling an evap code but I believe that is unrelated.

Any ideas?

 

Your fan might not be working

 

But there's the 4WD not working... you don't think the issues could be related? Maybe behind the dash? It's just such a weird coincidence that the heat and AC AND 4WD all went out at the same time.. right around the time that someone had pulled the dash apart, ya know?

 

If someone pulled the dash apart they may have messed something up. If your 4x4 is push button, is the light on on the 2wd button?

 

I believe so. (I don't have the truck here right now)

The lights looks normal until you try to go into 4WD. When you push the button, I think the 2WD light flashes once but never goes to 4WD.

 

I'd honestly pull the dash back out (however far it was pulled last time) and check all your connections, it's hard to say what it is without being there.

 

Thanks! I'm hoping I can find someone to do that this weekend. I just wanted someone to tell me I wasn't barking up the wrong tree with the idea that it's in the dash. I appreciate your input!

 

Your whole vehicle (electronically) is basically controlled from the dash so it's a great possibility. Good luck, i'll help you out if you still can't figure it out, You're welcome.

 

Understand air blows out but can you switch vents? {def, floor, vent}

Is this an automatic {"climate"} or manual heater control?

Cant hurt to check the IP fuses, end of dash driver side

Do you hear a faint hiss under dash with engine running?

 

As fog has eluded to, the problem is most likely vacuum related. Both systems share the manifold vacuum source and a leak at one results in neither functioning properly.

In a '96, the manual HVAC was the only option and all of the vacuum lines run to the HVAC control panel right under the radio. The most likely assumption is that the main vacuum connector was knocked off in one way or another during the stereo install.