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73-87 Chevy _ GMC Trucks => Interior & Equipment => Heating, Ventilation & Air Conditioning (HVAC) => Topic started by: kmanrsss on December 07, 2012, 11:54:49 am

Title: Hvac vacuum source
Post by: kmanrsss on December 07, 2012, 11:54:49 am

Should I be getting my vac source from the canister on the DS firewall for hvac controls? If so where should that be connected to, the back of the TB? This is on an 87. Thanks

Title: Re: Hvac vacuum source
Post by: Butalla on December 12, 2012, 09:56:53 pm

I'm not 100% certain on an '87, but on prior years, it comes from the vacuum tank on the firewall.  The vacuum can be drawn from about anywhere.

Title: Re: Hvac vacuum source
Post by: 79gmc15 on December 12, 2012, 10:40:34 pm

On my 79 the vacuum comes from a cross fitting behind the Carb on the manifold and goes to the ball like canister on the passenger side by the hinge. 

Title: Re: Hvac vacuum source
Post by: kmanrsss on December 14, 2012, 07:26:49 pm

Thanks guys. I'll look again in the morning, but I'm pretty sure there is only 1 opening on the vacuum ball.

Title: Re: Hvac vacuum source
Post by: bd on December 14, 2012, 07:38:58 pm

Vacuum is sourced from a fitting that threads into the intake manifold right behind the throttle body.  The vacuum line connects to a one-way check valve at the firewall and splits - one line goes to the vacuum reservoir, the other line passes through the firewall to the HVAC control panel mounted in the dash.

Title: Re: Hvac vacuum source
Post by: kmanrsss on December 28, 2012, 03:43:32 pm

thanks