63 SDV No Heat Defrost

[Tom Bahner]

Well, Cruisin is just about over for the season here in NE Ks. I had pulled and plugged the vacuum line to the  heater control valve on the engine during the summer to help the AC system out.

Well I hooked it back up for the heat and defrost for the occasional winter drives, and no air comes out of the floor ducts or defrost ducts. The air is toasty warm coming out of the AC vents. Guess the door directing airflow isn't working.

Is this controlled by vacuum only, off the heat/AC lever.  I haven't pulled the dash cover off yet to get to the control levers. I have pulled the lower cover off and couldn't see anything amiss there.  Don't hear any vacuum leaks coming from that area. Could the control head have just given up? I've read through the manual but couldn't find anything that addresses this problem.

Any help appreciated.

Tom B

[Tom Bahner]

Update - Pulled the dash cover off. All vacuum hoses are connected.

All the mechanical cables appear to be working at both ends of the levers. I can't see where anything happens when the top lever is switched to heat.  Seems like a door ought to change positions when Heat is selected. I can see the connection/door moving when the lever is moved to defrost.

Read the  manual a couple times but not understanding whats missing.

[3ft7bqmb7dryo]

Check on top of the heater/AC box for a vacuum line. There is a vacuum line that goes to a vacuum module. that module controls the heater/AC door.

The vacuum line plugs into a plastic fitting, so be careful and don't have gorilla hands. Check for vacuum at the hose, then test the module for holding vacuum.

[Tom Bahner]

Thanks Russ. I was looking at the manual and saw that module. Put my vac. pump on that line between the control levers and the module. Pumped it up to about 15 and didn't note any  change. Didn't have a good connection so slowly  lost pressure. Trying to figure out which line supplies vac. to the control levers. How much pressure is needed to hold the door open???

Thanks.

[3ft7bqmb7dryo]

Tony mentioned the start of the vacuum at the engine. Check the connection at the firewall, then the white plastic T type canister that is under the dash, to the left of the NSS/steering column. The white plastic T canister is a vacuum check valve, and that is where all the vacuum lines get the vacuum from.

Put your vacuum pump directly to the mode selector door, and see if it moves.  That way you are not including any possibly bad connectors/vacuum lines.

[Tom Bahner]

Thanks all for the responses. Well, I'm starting to get a little better understanding of what IS happening. Still haven't got to what should be happening.

I took the AC duct off to see what the mode door was doing. I found it in the AC position which directs air flow out the dash vents as expected. I pulled on the door and it slowly closed to the heat/defrost position. It appears there are two doors that operate when the control lever is moved. One the vacuum module is attached to in the middle and another to the passenger side of the air duct, attached together by a long rod. When the control lever is switched to AC, the vacuum module pulls the door to direct air out the dash. 

My question is what pushes the door the other way for heat/defrost?? It doesn't look like the vac module is a push/pull type affair. When the control lever is switched to heat, no vac is applied to the module. There is a spring attached to the bellcrank on the passenger side but its not enough of a spring to pull the door shut to the heat/def. mode.

This is probably clear as mud. I can get heat/def. now but hate to not fix the problem while I have it tore apart. If you know what I'm missing, any comments appreciated.

Tom B

[3ft7bqmb7dryo]

I looked at a assembly, and it looks like the air flow starts the door to move, and then the spring takes over and closes the door.

[Tom Bahner]

Thanks Russ.. It didn't look like there was any other components involved is these two doors. The right one must be hanging up some. I'll look at it some  more.

Tom B

[Tom Bahner]

Update - Well, I now have full operation of the heat/defrost and AC mode doors. I took the AC vent air plenum off the main plenum so I could see what the doors were doing. This is looking through the glove compartment.  Picture 1. When the Heat/AC control lever is switched to AC, the Vacuum Module hidden behind the flex tube, opens this door and one on the far right side of the Heat/Def plenum, allowing air flow to the AC vents. There is a rod on top of the plenum connecting the two doors.

Picture 2

 When the control lever is moved to Off or Heat, vacuum is released from the vacuum module, and a spring located on the far right door(this door  is located in the plenum so you can't see it, but you can see linkage on top of the plenum) is supposed to pull these doors closed to keep air flow in the main plenum. You can see the spring behind the wires.  After 50 years, the door axel and linkage was binding enough that the spring couldn't pull the doors shut. This left the doors directing air flow to the AC vents all the time.

To resolve this, I Rube Goldberg'd the spring to the linkage on the door in the 1st pic. I put just enough tension on it to pull the door shut, but not enough to overpower the vacuum module. So far it works perfectly.

This probably makes little sense to anyone that hasn't been in the heat/AC system yet but thought I'd throw my resolution out there in case they don't want to tear the whole plenum out. Sorry, I haven't figured out how to place the photos where I need them yet. Yes, I know it isn't factory correct, so don't whip me with a wet noodle. But, it works.

Tom B

[3ft7bqmb7dryo]

Enjoy the heat in your car. Work well done.