Heater core?

[PStansberry78]

I've been troubleshooting an issue with my heater not working.

So far, I've replaced a broken control knob, discovered and fixed an issue in the control unit (Linkage cable brackets broken so not changing mode.), and a dead blower motor relay (Replaced. Blows fine now.).

The issue now is that when it's set to defrost it only blows hot for about 30 seconds... and it IS hot. After that, it cools to ambient temperature as if the heater core shut off.

Could it be the heater core itself? That seems unlikely considering it does get hot every time when you first turn it on.

 

[Bobmbx]

Disconnect the electrical connector on your AC compressor, then hit the defrost again. I bet it stays hot.

When using the "Defrost" mode, the AC kicks on to dehumidify the air before it gets to the windshield.

If this is whats happening its a normal thing.

 

[PStansberry78]

OK. I'll try it. But if that's the case, how would it actually clear the windshield?

 

[larrydd999]

That's a normal situation, the A/C dries the air and the heater warms it. My '92 has a working A/C and my '94 is waiting for me to have time to rebuild it. The '92 clears the windshield much faster under similar conditions than the '94.