AC & Heat selection and vents

[RustyHalo70]

I've had some work done on m 85 GMC High Sierra, C2500 model. He upgraded the AC to be able to fill with the newer freon and seal up any leaks. It blows cold great also and not leaking.

When selecting between AC, Heat, Vent, etc it will not switch.

And, it's blowing Heat no matter what is selected.

So it blows cold for a while and then it eventually starts to be hot because the Heat is blowing all of the time.

I did replace the head unit a few months ago, was really a fan issue, but I left the new one installed.

Thanks in advance for the help.

 

[Goldie Driver]

I've had some work done on m 85 GMC High Sierra, C2500 model. He upgraded the AC to be able to fill with the newer freon and seal up any leaks. It blows cold great also and not leaking.

When selecting between AC, Heat, Vent, etc it will not switch.

And, it's blowing Heat no matter what is selected.

So it blows cold for a while and then it eventually starts to be hot because the Heat is blowing all of the time.

I did replace the head unit a few months ago, was really a fan issue, but I left the new one installed.

Thanks in advance for the help.

The hot and cold select is a cable operation so I am guessing that is not hooked up. Sadly you would have to get back in to the dash to see. The others are controlled by vacuum and I would check to see if the main supply under the hood is still connected.