Long story short it seems two gremlins hit my a/c / heat system at the same time, and I don't know if they're related or not.

First the air temp control **** on the dash seemed to intermittently stop working in that the vent air would stay locked on one temperature regardless of where the **** was. Can't remember if early on the air temp stayed stuck on hot or cold. It may have been stuck on cold all along, can't quite remember, but either way the air vent temp has been stuck on full cold for a couple months now and that hasn't varied.

Next, the under-hood 15A fuse started blowing that I've been told power the compressor clutch relay and elec. fan relay, (but not the compressor clutch or the elec. fan themselves, I believe). It was blowing once every day or two so I got a bulk pack of fuses and just kept replacing it. This be the fuse...



After I found out what that fuse went to, admittedly using the shotgun approach I took a guess and replaced the compressor clutch relay. After replacing the relay I'm now seeing the fuse blow only every week or two, as opposed to every day or two like it was before.

So now I'm still faced with the temp control **** that doesn't seem to work. I'm leaning away from the idea that the cable's simply become disconnected because when I move the **** I can hear a thump inside the dash that I interpret to be the temp mix door moving. Also, when the a/c is on and I move the lever from full cold to full hot, with my hand at the vent I can feel a change in the air...it slows down just barely, as well as drops in temp only very slightly, so it's still a/c cold.

So, questions... Other than having a loose cable on the air mix door in the dash, what can cause an a/c system to continue to blow cold air when the temp control **** is in the hot position?

How would the fuse that keeps blowing be associated with this air temp problem, if at all?

And lastly, if there IS no other possible solution to the temp control problem other than a loose cable, what's the best way to get to this cable to at least examine it and potentially reattach it?

 

Look up to the left corner of the bottom of the HVAC Unit from the passenger footwell.

There should be a simple bell crank protruding out of the HVAC Unit with a push-pull cable attached to it. This is the Blend Air Door control.

While looking at the bell crank, operate the temp slider on the Climate Control Panel from heat to cold. See if the cable/bell crank freely moves.


If there is no, or little, movement at the bell crank, remove the Climate Control Panel and look at the back of it. Operate the temp slider and see if the cable is moving. If not, it may be disconnected at the back of the control panel.

 

Maybe the heater core is clogged up? If it has a coolant control valve for the heater core it may be stuck closed.

 

Thanks Ken that sounds like good advice. If I can confirm circulation through my heater core that's exactly where I'll be going next.

Actually '90, since it seems like the temp control door is still sounding like it always has I was leaning toward the idea that maybe somehow I've lost circulation through the heater core. Here's my valve...



The part with the star is connected to a vac line and is the actuator to the valve. What kind of tests can I do to put this valve through it's paces where I should be able to observe it in both it's open and closed positions?

 

The valve has a spring and it's default position is open, when vacuum is applied it closes. Don't remember if the rod would be out or in for open, but generally out and your's looks to be in. Start the engine, put the control to heat and see where it is. Pull the vacuum line off and if the valve moves then that means it was closed when it should've been open. You should be able to pull or push the rod with the vacuum off and it'll spring back. If that's the problem, a quick fix is leave the vac hose off and plug it.