85 Heater stuck
Thread Starter
Intermediate
Joined: Apr 2009
Posts: 47
Likes: 0
From: Albuquerque NM
85 Heater stuck
Hi all,
I am new to vettes and need some help. I have seen a lot of posts about HVAC problems on newer vettes with the automatic climate control but I can’t seem to find anything for an 85 with just a normal old fashion climate controller.
Here is my problem: no matter what I do from the inside, the only think that comes out of the vents is hot air. There is a device under the hood on the passenger side that if I hold the plunger in, it will blow cooler air. The selector under the hood is spring loaded somehow and appears to be disconnected from the HVAC controller. Does this connect directly to the dash unit or is there a step in-between that I need to check? What else could it be?
I am new to vettes and need some help. I have seen a lot of posts about HVAC problems on newer vettes with the automatic climate control but I can’t seem to find anything for an 85 with just a normal old fashion climate controller.
Here is my problem: no matter what I do from the inside, the only think that comes out of the vents is hot air. There is a device under the hood on the passenger side that if I hold the plunger in, it will blow cooler air. The selector under the hood is spring loaded somehow and appears to be disconnected from the HVAC controller. Does this connect directly to the dash unit or is there a step in-between that I need to check? What else could it be?
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
The hot water valve out under the hood (which you are describing) is not your problem. Or not Causing this problem. The cause is the blend door within the heater box, above the passengers feet.
On the '85 this door is Cable operated, from the lower lever on the heated control unit. If you remove the hush panel on the passenger side (under the dash) you will expose the cable and the connection to the blend door operating linkage.
You will need to verify that the cable is working. Could be the cable is broken, could be a bad connection to the door linkage, could be the linkage or something inside the heater box (there is a plastic connector Inside there that is prone to failure, now after 25 years..). Could also be a problem right at the heater control - there is a small spring washer that holds the eyelet end of the cable onto a plastic pin on the control, and I have had that washer fall off allowing the cable to become disconnected from the control...
Other than this blend door/temperature control Everything else about the HVAC system operates by Vacuum, including the hot water valve you are describing out under the hood.
On the '85 this door is Cable operated, from the lower lever on the heated control unit. If you remove the hush panel on the passenger side (under the dash) you will expose the cable and the connection to the blend door operating linkage.
You will need to verify that the cable is working. Could be the cable is broken, could be a bad connection to the door linkage, could be the linkage or something inside the heater box (there is a plastic connector Inside there that is prone to failure, now after 25 years..). Could also be a problem right at the heater control - there is a small spring washer that holds the eyelet end of the cable onto a plastic pin on the control, and I have had that washer fall off allowing the cable to become disconnected from the control...
Other than this blend door/temperature control Everything else about the HVAC system operates by Vacuum, including the hot water valve you are describing out under the hood.
Team Owner
Joined: Jan 2003
Posts: 20,322
Likes: 248
From: Summerland B.C. Canada
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
if the hot water valve vacuum has gone away, Temporarily, till you find out what happened to the vacuum, you can drill a small hole in the arm, and tywrap it in the closed position. Otherwise, it will be in the full hot open position
Thread Starter
Intermediate
Joined: Apr 2009
Posts: 47
Likes: 0
From: Albuquerque NM
Ok, I found the cable that comes from the back of the control unit. It goes to a Y piece of metal. Moving the temp selector back and froth moves that Y piece of metal. That cable attaches to one side of the Y but there isnt anything attached to the other side. It looks like there should be because there is a plastic retainer but there isnt anything attached to it. I cant find anything around there that looks like it should attach to it. Anyone know what is missing?
I used a tie to close the valve so it isnt blasting hot air at me all the time, thank you for that tip.
I used a tie to close the valve so it isnt blasting hot air at me all the time, thank you for that tip.
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
That "Y-piece" or "bellcrank" should have a link connected to it which runs forward through an opening in the plastic heater box housing and connects inside to the flapper door which directs hot/cold air flow.
Neither of the links provided by agent86 really shows the mechanical arrangement of that actuating linkage.
You Might, perhaps, be able to spot the linkage arm by looking thru the opening in the box with a flashlight, but It's a very small hole. More likely you will have to disassemble the heater box to find the link and reconnect it to the arm, a lot of work but no alternative.
Right now you have no connection between the heater control head and the temperature control door - therefore you have no control over the air temperature.
Neither of the links provided by agent86 really shows the mechanical arrangement of that actuating linkage.
You Might, perhaps, be able to spot the linkage arm by looking thru the opening in the box with a flashlight, but It's a very small hole. More likely you will have to disassemble the heater box to find the link and reconnect it to the arm, a lot of work but no alternative.
Right now you have no connection between the heater control head and the temperature control door - therefore you have no control over the air temperature.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
