gene2661

Lately I have been having an issue with hot air coming through my vents instead of cold. Sometime its cold and then it turns hot. I think I have a problem with my doors opening and closing on the duct system. I would leave with air on an its cold then all of a sudden it get hot air. After I have stopped for awhile it will be cold again. The duct door system works on vacume doesnt it? could I have a bad vacume line and where does the duct system pick up the vacume from the engine? really need help on this one. This is a 1987 Corvette

AGENT 86

The temp door is controlled by an electrical motor. It sounds like you may have broken a clip on the rod that joins motor and door, allowing the door to swing from cool to heat.
The rest of the doors are controlled by vacuum.
Can you switch from floor to vent, etc ?

http://members.shaw.ca/dankai/HVAV'S.pdf

http://members.shaw.ca/dankai/HVAC%20Electrical.pdf

AGENT 86

Oops, if you have a manual control HVAC, the temp door is controlled by a cable.

gene2661

I have the electronic ac control head not the manual. If I take the temp setting to 90 then a door closes and air goes to the floor. Take it back to 60 and the air comes to the top center. But stays hot-sometimes. The air is cold at times then get hot coming from the same center top vents. Once I shut the system down and I had nothing but hot air came from the floor vents. I took the AC control head out of the dashto see if anything was broke and found that its just a module. Something that I havent been able to find in any catalog. Could the control head be bad? If so where do I get a new one? I just love this forum so much info here Thanks for the responce and the help so far.

Salvi 07

recharge the ac?

gene2661

AC Charge is ok But what about having the ac control head -C68- tested can it be ested and where

93v

Are you getting any codes from the hvac head?On my 93 you can pull codes from the head,not sure if you can do that on your year.

gene2661

I know nothing about getting codes from the hvac head its a 87

93v

If you do a search you should be able to find how to do it,if not I can look in my helms book and let you know how it's done on a 93.Don't know if that will work on your year.

AGENT 86

Remove the blower control module from the housing. Look into the opening while someone changes the temp from high to low, low to high(auto mode), you should be able to see the door opening and closing.
If you don't, one of the rod clips being broken, is a likely suspect.

SunCr

As above - if it doesn't move or it flops around, you know it's probably the linkage or motor. If it moves, the Evaporator is probably icing over meaning something is wrong with the charge or Low Pressure Switch.

gene2661

I will try that It makes sence here is a little more info With the HVAC shut off I sometimes get hot air blowing on my feet That shouldnt be right??? The temp setting is on 60 when I turn it back on I get hot air (sometimes) from the center vents I also will have the ac checked But I do get cold air sometimes could something be going on with maybe low pressure??? Thanks for the help

gene2661

Ok I had the HVAC control head checked out.. Its ok what is my next step... it still blows hot air sometimes.. is there another module that controls the blend door??? and how and where is it. How do i get to the blend door?

gene2661

Hey Agent 86
Where would I purchase the plastic clips on the blend door motor fot my 87? Would that be a item that will be hard to find?