I am almost done with the complete restoration of my 1990 GT, but my HVAC is acting all funny. The Temp controls work, but it blows air through all the vents in equal amounts. Sliding the lever does not change anything unless I put it in the "off" position which stops air coming through.

What shall I look for?

The car has no vacuum leaks whatsoever... Am I missing a component within the HVAC?

Thanks in advance,

Alex

1990 928 GT
1984 928 S2 Manual (GTS Gearbox and Manual PSD)

 

Alex, look for the obvious first. Do you have all elect. wiring hooked up to the climate control unit in the console?

 

I think you may be wrong about not having vacuum leaks. All of the vents are operated by vacuum control. Check the footwell blowers and see if they're pumping out air. If you can't get them to open, you've got a leak somewhere. The footwell requires vacuum to open the vent, otherwise it defaults to the "closed" position.

Check out this site (thanks to John Pirtle) for more information:

http://members.rennlist.com/pirtle/svc_act.html

 

As I said the HVAC is pumping air everywhere, including the footwell vents...

BTW, the engine came out 2.5K miles ago and underwent a total rebuilt - the only original parts left are the pistons, crank, block and heads... Everything else is NEW, including all vcacuum lines, hoses etc...

 

I agree with Dave, recheck the vacuum lines under the console. Check them one by one. Other than that you may have to go through the troubleshoot settings in the WSM. But check out Pirtle's site, that's where I fixed all my leaks with the HVAC.

 

Alex,

I'm going through the same job right now on my 90GT, and although I thought all the lines were okay, you can't test them without disassembly of the center console to expose the vacuum manifold. There is a supply line that goes through the firewall and gets it's vacuum from a small line right near the top left of the firewall. There is a tee fitting that provides vac to the flappy solenoid, and the other line leads to the center console.

This line that feeds into the console goes to the manifold. With all the manifold electric solenoids normally closed, it's hard to troubleshoot the vacuum problems. Once exposed by taking off the console, you are able to test the multi-colored lines individually to test the vacuum diaphrams which develop pin-hole leaks in them. My car had 4 out of five defective, including the infamous AC recirculating diaphram located under the AC/heater blowerin the right front well just below the windshield.

The Pirtle write up is invaluable in finding and fixing the HVAC systems. Your symptoms show all the signs of failing vacuum diaphrams. I will be posting a write-up of R&R of the AC recirc diaphram once I'm finished. I also discovered a way to replace the comb-flap control diaphram WITHOUT REMOVING THE DASH, POD, AND AIRBAG!

Also, unless you have recently exchanged the heater control valve, it will need to be replaced($12 USD). The vacuum diaphram tends to leak, and the rubber bushing in the valve also deteriorates and even if the vac is working, the bushing swells from hot coolant and fails to seal. Replacing this will improve your AC operation immensly.

Doc 90GT in resto, working HVAC problems,

 

While you can remove the vacuum solenoid manifold to test the actuators, there is another way.

Remove the cover from the driver's side of the center console.
Look next to the driver's calf and find the bundle of small colored plastic tubes.
Get a few inches of small rubber or soft plastic tubing that is a snug fit on the colored tubes.
Use a sharp razor knife to cut the orange tube. Apply vacuum to the end that runs up into the dash (not the end that runs forward to the solenoid manifold). If the orange tube holds vacuum, splice it back together with the small tubing. If it won't hold vacuum, plug the other end (the end that runs forward to the solenoid manifold) until you get a round tuit and replace the leaking center comb flap actuator.
Repeat on the blue, yellow, green lines.
Do not cut or test the white (heater valve) line or the black (supply) line.