'73 vacuum question
Thread Starter
Racer
Joined: Oct 2005
Posts: 469
Likes: 0
From: West Slope of the Sierras California
'73 vacuum question
Any one care to help this old fart out here? Just exactly WHERE should the vacuum supply line be coming from for the heat/a/c control? My '73 has a line with a teeny hole in it, prolly 1/16" and comes from the rotary valve through the firewall near the distributor. (I bought the car with a 383 in it and most of the a/c components were left off and that tiny vacuum line just dangling.) Can one possibly pull enough vacuum through that small a hose? Just got a set of new headlight vacuum hoses from Zip and their diagram shows the supply for both teeing off of the manifold, then another troubleshooting guide I got here on the forum doesn't show a tee from the headlight supply going to the heat/a/c. I'm confused!
Thanks....Randy
Thanks....Randy
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
On a 72 I believe that little line Ts in on the yellow striped hose that feeds the wiper door vac relay. The pic below is of a 78 and at about 2 oclock you can see where the tiny hose Ts in to the headlight vacuum. I cant recall on your 73 exactly how the little line Ts in. The way the 78 Ts in should work ok.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The vacuum lines from the rotary heat/cool control head are smaller. They don't require much airflow to actuate the dampers, etc....as long as there aren't any leaks. Use the Chevrolet Chassis Service Manual info/diagrams to trace-out the vacuum lines. There is one vacuum 'supply' line to that rotary valve, and up to 8 'feeder' lines to the various dampers for duct door operation, etc. Buy an inexpensive vacuum gauge set at local auto store to test the system out.
Race Director
Joined: Jul 2001
Posts: 15,892
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I think that's how British people with a hare lip pronounce 'umbrella'.
The source of vacuum for the Astro Ventilation system is a T fitting on the larger of the two tubes downstream of the vacuum check valve.
The source of vacuum for the Astro Ventilation system is a T fitting on the larger of the two tubes downstream of the vacuum check valve.
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Safety Car
Joined: Apr 2000
Posts: 3,802
Likes: 61
From: Wichita KS
I just replaced the hoses on my 72 with A/C and the heater-A/C vacuum line does T off the hose with the yellow line to the wiper door relay.
The new line had to be cut and the T installed per the Zip instructions. The cut is made right by the passenger side hood latch.
cc
The new line had to be cut and the T installed per the Zip instructions. The cut is made right by the passenger side hood latch.
cc
Thread Starter
Racer
Joined: Oct 2005
Posts: 469
Likes: 0
From: West Slope of the Sierras California
Thanks all for your input. 7T1vette has me figured out. Guess that system doesn't need quite as much vacuum to operate as opposed to the headlights with the bigger actuators. Had my whole dash out checking things with a vac pump and it turned out being a bad rotary valve....I hope. Will know for sure when it's all back together.
