ac help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

6772king · 11-12-2002, 07:36 PM

i know i dont need it now but hopefully someday i have a 6772 with working air. my question conserns the vac hoses could anyone give me some help on routing from the canister on the side of the heater box then to the switch then T of and go to each one of the vac actuaters????????????? that is where i get lost and what about the heater valve what controles it,in pics it look like vac but where does it come from and is the valve just for shuting the heat of when you running the ac any help would be greatly apperciated thank's sean

Fred T · 11-12-2002, 07:52 PM

All directions are looking down and facing the dash, driver's side is the left. Line from the reservoir (right side) goes to the right port of the vacuum switch on the control head.

From the center port the line goes to the door diaphragm at the passenger's feet, when all the levers are to the left this vent door will open.

There is a tee in this line, which goes to the outside air diaphragm on the firewall, passenger side in the engine compartment above the heater. This controls the fresh air that goes in through the heater/ a-c unit.

From the left port on the control head vacuum switch the line goes to the water valve, which opens when vacuum is applied. This valve is in the supply side to the heater, where the hose turns the corner at the fender and goes back to the heater.

This is all shown on page 1a-32 of the factory shop manual, a tool well worth the ~$30 investment.

**GMCPaul** · 11-13-2002, 07:34 AM

Here you go this is what you need

Thats out of the Factory service manual. They are a wealth of information on everything on these trucks.
GMCPaul

6772king · 11-13-2002, 08:29 PM

thanks alot fred and gmc paul one other question ????? the vac controls that i have only have 2 ports does that mean i didnt have the heater shut off valve again thank you sean

Fred T · 11-14-2002, 03:13 AM

I can't answer that one. If you don't get another response, come to GMC Paul's web page and ask him there.

**GMCPaul** · 11-14-2002, 05:26 AM

The only difference on your 67 is the fact that there is no vacuum line for a water valve. So just disregard connection shown in picture for it, otherwise everything is the same.
GMCPaul

Project1970 · 11-14-2002, 05:47 AM

Ah...that explains that useless canister on my truck.

I removed it and put the vacuum switch for my 700R4 there...it'd long been disconnected from anything other than engine vacuum.

My A/C works, but it is a bit of a mess...

6772king · 11-14-2002, 06:27 PM

thanks alot guy's that should get me going again!!!

11-12-2002, 07:36 PM	#1
6772king Registered User Join Date: Feb 2002 Location: grove city pa usa Posts: 628	ac help i know i dont need it now but hopefully someday i have a 6772 with working air. my question conserns the vac hoses could anyone give me some help on routing from the canister on the side of the heater box then to the switch then T of and go to each one of the vac actuaters????????????? that is where i get lost and what about the heater valve what controles it,in pics it look like vac but where does it come from and is the valve just for shuting the heat of when you running the ac any help would be greatly apperciated thank's sean Attached Images __________________ 67 chevy short step 2wd 427 71 chevy short fleet 4x4 396 72 gmc jimmy 2wd 377 71 chevy blazer 4x4 454 69 chevy longhorn 5.9l cummins 72 chevy 400 2wd custom camper 67 chevy lwb 4x4 454-in pieces 67 chevy panel soon 4x4-400 67 gmc dump 4x4 1 ton-305 WTF!! 72 chevy 3/4 ton 4x4 burb 350 70 chevy panel 2wd 302 5 speed tko "THERE IS NO REPLACMENT FOR DISPLACMENT"!!!!!!!

11-12-2002, 07:52 PM	#2
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	All directions are looking down and facing the dash, driver's side is the left. Line from the reservoir (right side) goes to the right port of the vacuum switch on the control head. From the center port the line goes to the door diaphragm at the passenger's feet, when all the levers are to the left this vent door will open. There is a tee in this line, which goes to the outside air diaphragm on the firewall, passenger side in the engine compartment above the heater. This controls the fresh air that goes in through the heater/ a-c unit. From the left port on the control head vacuum switch the line goes to the water valve, which opens when vacuum is applied. This valve is in the supply side to the heater, where the hose turns the corner at the fender and goes back to the heater. This is all shown on page 1a-32 of the factory shop manual, a tool well worth the ~$30 investment. __________________ Fred There is no such thing as too much cam...just not enough engine.

11-13-2002, 07:34 AM	#3
GMCPaul Senior Member Join Date: Mar 2000 Location: Rockville,In. USA Posts: 3,718	Here you go this is what you need Thats out of the Factory service manual. They are a wealth of information on everything on these trucks. GMCPaul __________________ Secure Online Catalog for-GMCPauls Truck Parts Email- GMCPAULS@GMAIL.COM

11-13-2002, 08:29 PM	#4
6772king Registered User Join Date: Feb 2002 Location: grove city pa usa Posts: 628	thanks alot fred and gmc paul one other question ????? the vac controls that i have only have 2 ports does that mean i didnt have the heater shut off valve again thank you sean __________________ 67 chevy short step 2wd 427 71 chevy short fleet 4x4 396 72 gmc jimmy 2wd 377 71 chevy blazer 4x4 454 69 chevy longhorn 5.9l cummins 72 chevy 400 2wd custom camper 67 chevy lwb 4x4 454-in pieces 67 chevy panel soon 4x4-400 67 gmc dump 4x4 1 ton-305 WTF!! 72 chevy 3/4 ton 4x4 burb 350 70 chevy panel 2wd 302 5 speed tko "THERE IS NO REPLACMENT FOR DISPLACMENT"!!!!!!!

11-14-2002, 03:13 AM	#5
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	I can't answer that one. If you don't get another response, come to GMC Paul's web page and ask him there. __________________ Fred There is no such thing as too much cam...just not enough engine.

11-14-2002, 05:26 AM	#6
GMCPaul Senior Member Join Date: Mar 2000 Location: Rockville,In. USA Posts: 3,718	The only difference on your 67 is the fact that there is no vacuum line for a water valve. So just disregard connection shown in picture for it, otherwise everything is the same. GMCPaul __________________ Secure Online Catalog for-GMCPauls Truck Parts Email- GMCPAULS@GMAIL.COM

11-14-2002, 05:47 AM	#7
Project1970 14.1 @ 96MPH Join Date: Jul 2001 Location: Mesa, AZ Posts: 2,811	Ah...that explains that useless canister on my truck. I removed it and put the vacuum switch for my 700R4 there...it'd long been disconnected from anything other than engine vacuum. My A/C works, but it is a bit of a mess... __________________ Project1970 - LS1 Swap Complete!

11-14-2002, 06:27 PM	#8
6772king Registered User Join Date: Feb 2002 Location: grove city pa usa Posts: 628	thanks alot guy's that should get me going again!!! __________________ 67 chevy short step 2wd 427 71 chevy short fleet 4x4 396 72 gmc jimmy 2wd 377 71 chevy blazer 4x4 454 69 chevy longhorn 5.9l cummins 72 chevy 400 2wd custom camper 67 chevy lwb 4x4 454-in pieces 67 chevy panel soon 4x4-400 67 gmc dump 4x4 1 ton-305 WTF!! 72 chevy 3/4 ton 4x4 burb 350 70 chevy panel 2wd 302 5 speed tko "THERE IS NO REPLACMENT FOR DISPLACMENT"!!!!!!!



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