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AC Vacuum Controls [message #343728] Mon, 27 May 2019 17:44 Go to next message
Carl S. is currently offline  Carl S.   United States
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
Senior Member

My coach is a '75, so the dash air conditioning airflow is pretty dismal in the first place, but there is almost no air at all coming from the registers at the right side of the dash. I started checking vacuum to the servos and found no vacuum at that line. Working my way back, I found I didn't have any vacuum coming from the engine to the little round vacuum can on the firewall.

Somehow, the line had come disconnected from the intake manifold. I re-connected it, thinking that would fix everything, but it is still not working properly. Now, when I start the engine, the recirc door closes, and the heater valve closes, but there is still no vacuum at the right side servo. Also, when I turn on the heater, the heat control valve stays closed. It looks like all the vacuum lines are hooked up to the dash control correctly, but things are still not operating like they should be.

Any ideas?


Carl Stouffer '75 ex Palm Beach Tucson, AZ. Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
Re: [GMCnet] AC Vacuum Controls [message #343735 is a reply to message #343728] Mon, 27 May 2019 20:01 Go to previous messageGo to next message
Sammy Williams is currently offline  Sammy Williams   United States
Messages: 522
Registered: August 2010
Karma: -2
Senior Member
Yes.
Check vacuum lines to ensure they are not blocked.
Check your vacuum mounting at the manifold to insure they are correctly
hooked up.
Is the vacuum “manifold “ at the hvac box hooked up properly and the lines
not clogged?
Check your vacuum parts on the hvac box to ensure they are free moving and
check your door linkages to ensure they work properly.
Check the cables comping from the controls to the box. Ensure they move
fully.

Sammy

On Mon, May 27, 2019 at 19:31 Carl Stouffer via Gmclist <
gmclist@list.gmcnet.org> wrote:

> My coach is a '75, so the dash air conditioning airflow is pretty dismal
> in the first place, but there is almost no air at all coming from the
> registers at the right side of the dash. I started checking vacuum to the
> servos and found no vacuum at that line. Working my way back, I found I
> didn't have any vacuum coming from the engine to the little round vacuum
> can on the firewall.
>
> Somehow, the line had come disconnected from the intake manifold. I
> re-connected it, thinking that would fix everything, but it is still not
> working
> properly. Now, when I start the engine, the recirc door closes, and the
> heater valve closes, but there is still no vacuum at the right side servo.
> Also, when I turn on the heater, the heat control valve stays closed. It
> looks like all the vacuum lines are hooked up to the dash control correctly,
> but things are still not operating like they should be.
>
> Any ideas?
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Re: AC Vacuum Controls [message #343737 is a reply to message #343728] Mon, 27 May 2019 20:24 Go to previous messageGo to next message
Matt Colie is currently offline  Matt Colie   United States
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
Senior Member
Carl,

Sammy could be right, but before you do much else, pull on the rubber connectors everywhere. I have had two of them split. They looked great, but I could not see the split until it was stretched.

If it is a problem with the selector valve, I can't help you at all.

Matt


Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
Re: [GMCnet] AC Vacuum Controls [message #343740 is a reply to message #343737] Mon, 27 May 2019 22:31 Go to previous messageGo to next message
jimk is currently offline  jimk   United States
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
Senior Member
Do you have the diagram of the all vac lines.
I can send one if you do not have.

On Mon, May 27, 2019 at 8:19 PM Matt Colie via Gmclist <
gmclist@list.gmcnet.org> wrote:

> Carl,
>
> Sammy could be right, but before you do much else, pull on the rubber
> connectors everywhere. I have had two of them split. They looked great,
> but I
> could not see the split until it was stretched.
>
> If it is a problem with the selector valve, I can't help you at all.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>


--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
Re: [GMCnet] AC Vacuum Controls [message #343762 is a reply to message #343740] Tue, 28 May 2019 14:01 Go to previous messageGo to next message
Carl S. is currently offline  Carl S.   United States
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
Senior Member

Thanks for the advice. I will check them methodically when I get some time after returning from a two week (non motorhome) trip to Alaska.

I do have the vacuum line diagrams and now, thanks to Daniel J. I have a color version.

It makes sense that some of the vacuum lines may have gotten dirt in them and might be clogged and I have repaired some of the nipples that were split, but there may be more. I'll look closely at those things.

Thanks again.


Carl Stouffer '75 ex Palm Beach Tucson, AZ. Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
Re: AC Vacuum Controls [message #343763 is a reply to message #343728] Tue, 28 May 2019 14:47 Go to previous message
JohnL455 is currently offline  JohnL455   United States
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
Senior Member
Use a stethoscope to trace the system starting at engine all the way through the valves to vac motors. You don't even need Ohms Law!!

John Lebetski
Woodstock, IL
77 Eleganza II
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