I've got a '70 series 1 that won't switch full airflow to the defrost ducts. I have good pressure coming out the front of the dash toward driver/passenger so the blowers seem good but living in Alaska, I need it all to go to defrost/defog the windshield. The car has a 350 swap done so original vacuum hoses have been lost to the ages. Is there an easy way for me to flip a flapper or something to force all air at the windshield all the time? I don't care if it can't be switched on/off. Thanks for any input.

 

The defrost vents are operated by a vacuum motor, which also introduces outside air. If your vacuum system is disconnected, the default condition is inside air (recirculate) and defrost vents "closed."

"Closed" is relative because the flaps within the ducts leading to the vents are undersized--allowing some air to pass through. If you remove them, or fix them in the open position, maximum air should flow to the windscreen as you desire. The fascia vents receive air flow regardless of the position of the defrost vent flap. To maximize the air out of the defroster, manually close the fascia vents using the small knob at the center of the ball. Hope this helps!

 

Also making sure the vent to the back seat is closed will increase air flow to the defrost vents and everything else in front.

At least it works that way in my Series 2. YMMV.
(';')

 

Varnish:


Why not rebuild the vacumn supply as it was. Just plumb in to the
ABC for the supply. The Jaguar heat system can't distinguish between GM vacuum and Jaguar vacuum.


My lump is plumbed that way. works slick.


Carl

 

There should be two lines coming into the cabin that end up behind the radio. One is hooked to the front round actuator that connects to the center vent in the center of the windshield.

Other also comes into the cabin... mostly likely all the small vacuum hoses are rotten, the plastic nipples broken off the heater controls behind the radio.

You do not talk about the heater working or not... nor the AC working?

All can be fixed... first start with the two lines into the cabin and looking at all the hoses...fixes are available.

 

I have the same problem. I just replaced driver's side fan with a GMC fan and used the original impeller (if that is the right word) and the air flow is good or better than the original. Tons of air coming out of the round facia vent but very little coming out of defrost.

On a series 1, the only vacuum-actuated flap is the one at the base of the windshield for the cold air intake. The defrost should work fine with it closed (in winter you don't want cold air coming in), so the only reason that there is no or little air going to the defrost is that the car/demist/facia lever switch is not working, or to put it more accurately the tube leading to the defrost is blocked.

Any advice before I pull out the console to look under there will be appreciated! No A/C on my car.

 

Note the age of this post

 

Thanks. I know. I figured it was better to resurrect this old thread than start another. And I wanted to correct the misinformation that the defrost flap is controlled by vacuum. (it may be true on S2, but not on S1)