1969 Mustang Heater Stuck on Defrost

[KipDurran 18]

Hello.

 

I have a 1969 Candy Red convertible I bought last week. The heater control seems to be stuck on defrost. So much so that a p.o. bent the heck out of the control lever. I have done a lot of searching but can't seem to find a solution to my problem.

 

I have taken the dash apart and have straightened out the heater control arm.

 

After removing the defrost and floor heating conduits I have exposed the heater box with the door that moves to change from defrost to floor heater. When the door is in the full defrost position it is very difficult to move back from there. It is not the cable as I have disconnected that and the door is still extremely difficult to move from the full defrost position. However, once is has started to move from there it seems to move ok.

 

I have tried to clean the inside of the box as best I can but to no avail.

 

Does anyone know of an easy fix for this? Do I have to replace the unit? (I am not really excited about that).

 

Thanks for any info.

 

Steve

[BinaryBo 10]

I have the same problem. I lubricated the shaft and the seal for the flapper, but it still gets stuck in defrost. It seems like the problem is the rubber seal around the flapper has gotten stiff and it is hard for it to change directions once it has been put into full defrost mode.

 

For now I have disconnected the cable and manually put the flapper halfway between heat and defrost. I am planning to upgrade to A/C soon so I haven't been too worried about it.

 

FordGuy69 solved the problem by trimming the rubber on the flapper:

http://www.1969stang.com/mustang/forum/showthread.php?p=120987

 

Also this person:

http://forums.vintage-mustang.com/vintage-mustang-forum/628950-1970-sticky-heater-heat-defrost-cable-alignment.html

 

That may work for you too.

 

Bo

[Kris 90]

I had the same problem with my box when I rebuilt it. It is either the hole that the flap rotates in on the case is worn causing it to not sit straight and get in a bind when it starts to rotate. Or the flap has rubber along the outer edges that slide up against the side of the case and make a seal so no air gets buy. I had this same problem before and after I complete rebuilt my box. All parts were media blasted and refinished and it still did this. I found that the rubber pieces along the side of the flap were the problem. The rubber was binding on the sides of the case so I took a little white lithium grease and put it on both sides of the flaps rubber edges to lubricate it. I kept rotating the flap by hand to work it in and it loosened up and worked perfectly. Don't put a crazy amount, just a little at a time until it starts to rotate smoothly. I did mine with the box out of the car but you may be able to access it in the car if you can take the floor duct plenum off or take off the dash pad and remove the defrost vent from the box to expose it. The rubber on the flap in my box was still nice and soft after I cleaned it when it was removed, so having the rubber become hard over time wasn't an issue in mine. Hope this helps.

Edited May 6, 2014 by Kris

[SA69mach 39]

Just finished repairing this on my 70 coupe. Same issue - very stiff arm, broken cable (due to stiff or seized arm)

 

I had to remove the box anyway, so, complete clean of the casing, axle and flapper. Had to slightly trim the cruddy edges off, and smooth down the inside of the box.

 

It is kind of a big job compared to the problem, but you gotta have a working defroster, and I am glad I took the effort and time. New seals, new cable, smooth working heater/defroster. Three good reasons to do it.

[69RavenConv 302]

Agree with Kris and SA69mach. On mine the hole for the "axle" is elongated. Best fix would be to disassemble and fit a new bushing but I got mine to work by a good cleaning, trimming the flapper and lubricating with white lithium grease.

[KipDurran 18]

Wow!

 

Thanks for all the quick replies.

 

You all have validated what i was thinking was the problem.

 

I think that I am going to bite the bullet and remove the whole box and rebuild it. Might as well replace the core too.

 

It doesn't really otherwise need it but I don't want to have to do it 5 years down the road after I fix everything up.

 

I know that there are rebuild kits for these things. Do they contain a replacement door seal as well?

[KipDurran 18]

Today I removed the heater box. It was not a hard as I had feared, although I figured out that I have to disassemble it in order to get it out from under the dash.

 

Indeed, it was the rubber seals that were causing the problem. What is dis was to slowly trim little bits from the edge until the door moves well. Hopefully this will solve the issue.

 

I am going to pick up a new seal kit tomorrow and put it back together with a new heater core.

 

I found something quite interesting inside the box. There was a bunch of that green DeCon rat poison pellets in there. Either a rat brought them in there or someone put them in there. I can just imagine what it would have been like had a rat gotten in and died. Wow.

[Chris'69Mach 23]

I got one for you .... My defrost lever would not move either ..... Look what I found in my heater box!

[KipDurran 18]

Holy crap,

 

What is that? Hamster bedding?

[Chris'69Mach 23]

Looked like a mouse nest .... they apparently were busy over a number of years. I was told the car was garaged for 20 years before I got ahold of it. Needless to say, the defrost lever works perfectly now LOL.

[proautomik 10]

anyone know where to get the door that changes it from heat to defrost?

[KipDurran 18]

I looked around and I could not find the door separately, it seems to be non-removable from the housing. Trimming the rubber gasket was a little tricky to do but seems the best solution and so far it is working very well for me.