I just bought a 99 Blazer 4x4 LE with 134000 miles. I have the following issues...
1. A/C works great but when I put the selector switch to heat, still blows Ice cold, also Dash Defrost blows Ice cold. I put the Selector switch back on A/C and the temp control to hot the A/C should blow hot but still blows Ice Cold?

2. AM/FM/CD Radio, only speakers that work are the Passenger Door and Passenger Dash Tweeter and Driver Side Dash Tweeter. I checked all other speakers wiring which is good and the speakers Ohm out good so they are not blown, Is it a bad head unit?

3. In the center of Firewall is a vacuum actuator with an electrical connection and supposed to be two hose connections, where do the hoses go too, (see pic).

Thanks, Al

 

the actuator on the firewall has something to do with the 4 wheel drive if im not mistaken. i think that it is suppose to go to the transfer case.
as far as the stereo situation, did you try to take a known good speaker and hook up to the factory wiring? i had the same kind of issue. figured out the speakers were actually bad.
the two hoses that go into the firewall in the first picture are your heater hoses. if those are not connected to the engine, then you wont have heat. if they arent connected it might be because the heater core is broken. then you will have to either change it, or get it changed.
just a start until more people chim in.

 

I had a problem with my heater also not hot and cold, but selecting were the air comes out also my 4wd drive stopped working I ordered a new vacuum actuator thinking that was the problem. But when I went to replace it I discovered it was fine. So I ended up replacing all the vacuum hoses for $4.00 and presto the 4wd works and the directional air works. The stupid thing was I put up with it for over a year.