Referral wanted to repair HVAC control head- 1970

[Mark E.]

Who are the best resources for repairing the HVAC control module in a 1970? I didn't see anyone listed in the Driveline that just arrived.

I test all 7 vacuum ports across all 8 operating modes and all work fine except the AC port (tan line; port 8*). It should have vacuum in OFF, AC MAX, and AC NORM modes but there's no vacuum in OFF and AC MAX. Which means no air flow through the dash vents in AC MAX mode.

*There are 7 vacuum ports numbered 1,2,3,5,6,8,9 in the CSM (4 and 7 skipped).

Thanks!

[Edward J.]

Re: Referral wanted to repair HVAC control head- 1970

Mark, a/c max I believe is the recycle door, which take the cool air inside car and recycles to aid in cooling when hot air outside raises the temp of inside air. Is that vacuum line hooked up? I don’t have a diagram, but I believe that hose routes outside in the wiper cowl area on pass. Side, maybe broken even?

[Mark E.]

Re: Referral wanted to repair HVAC control head- 1970

Mark, a/c max I believe is the recycle door, which take the cool air inside car and recycles to aid in cooling when hot air outside raises the temp of inside air. Is that vacuum line hooked up? I don’t have a diagram, but I believe that hose routes outside in the wiper cowl area on pass. Side, maybe broken even?

Here's what I've done:

- Removed the 7 line vacuum manifold from the vacuum rotary switch on the control unit.

- Tested each line with a MityVac. All valves work and hold vacuum (hot water valve, outside air diaphragm (in plenum), recirculated air diaphragm (in kickpanel), diverter door diaphragm (under dash) and defog/deice diaphragm).

- Tested the vacuum rotary switch with a MityVac. I hooked up the MityVac to the supply port (black) and plugged the other ports. I then individually unplugged and attached a vacuum gauge to each port. While setting the left wheel to each position (Off, Max, AC,...) I checked if vacuum was held or vented, and compared the result to the table in the CSM schematic.

Everything works as expected except port 8. It should hold vacuum in OFF and AC MAX, but doesn't. This port is connected to the diverter door with the tan line to hold it in the upper outlet position when vacuum is applied.

I'm thinking the vacuum rotary switch isn't working properly. I learned a repro switch is available from the parts houses for about $24 so I'm thinking of replacing it and hoping that solves the problem.

Any suggestions?