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[GMCnet] Front dash A/C issues [message #319357]

Tue, 20 June 2017 20:22

BobDunahugh

Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA

Karma: 11

Senior Member

Leaky compressor issue solved. I got a Sanden compressor from Applied. Very nice, and simple to install. I flushed it, and put in Oil for R-12. ( got lots of R-12 ) Replaced all electrical components. Now that all works nicely. Next the vacuum components. Nothing works. Is the major problem generally the vacuum valve in the dash control? Then there's the 5 I think diaphragms. It's a 1978 GMC. Bob Dunahugh
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Re: [GMCnet] Front dash A/C issues [message #319358 is a reply to message #319357]

Tue, 20 June 2017 20:54

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

BobDunahugh wrote on Tue, 20 June 2017 20:22

Leaky compressor issue solved. I got a Sanden compressor from Applied. Very nice, and simple to install. I flushed it, and put in Oil for R-12. ( got lots of R-12 ) Replaced all electrical components. Now that all works nicely. Next the vacuum components. Nothing works. Is the major problem generally the vacuum valve in the dash control? Then there's the 5 I think diaphragms. It's a 1978 GMC. Bob Dunahugh

I wouldn't think ALL the diaphragms are bad. The vacuum valve in the dash control is repairable, if that is your problem.

http://www.gmcmhphotos.com/photos/hvac-dash-and-blower-control/p58077-hvac-control-panel-function-switch.html

Here's the 1976 heater/ac vacuum "schematic"

http://www.gmcmhphotos.com/photos/color-hvac-troubleshooting-charts/p22990-hvac-diagram-color-comp.html

I would check that I got vacuum at the "vacuum tank" (upper right hand corner of the color diagram, physically located on the driver side of the blower box). And go from there.

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Re: [GMCnet] Front dash A/C issues [message #319359 is a reply to message #319357]

Tue, 20 June 2017 21:17

C Boyd

Messages: 2629
Registered: April 2006

Karma: 18

Senior Member

The 78 (9) port control valve is available from Jim K for ~ $40. I got the 2 port valve for the heater shut off to clean up and seal.

BobDunahugh wrote on Tue, 20 June 2017 21:22

Leaky compressor issue solved. I got a Sanden compressor from Applied. Very nice, and simple to install. I flushed it, and put in Oil for R-12. ( got lots of R-12 ) Replaced all electrical components. Now that all works nicely. Next the vacuum components. Nothing works. Is the major problem generally the vacuum valve in the dash control? Then there's the 5 I think diaphragms. It's a 1978 GMC. Bob Dunahugh
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C. Boyd
76 Crestmont
East Tennessee

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Re: [GMCnet] Front dash A/C issues [message #319361 is a reply to message #319358]

Tue, 20 June 2017 21:35

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

A Hamilto wrote on Tue, 20 June 2017 20:54

BobDunahugh wrote on Tue, 20 June 2017 20:22
Leaky compressor issue solved. I got a Sanden compressor from Applied. Very nice, and simple to install. I flushed it, and put in Oil for R-12. ( got lots of R-12 ) Replaced all electrical components. Now that all works nicely. Next the vacuum components. Nothing works. Is the major problem generally the vacuum valve in the dash control? Then there's the 5 I think diaphragms. It's a 1978 GMC. Bob Dunahugh

I wouldn't think ALL the diaphragms are bad. The vacuum valve in the dash control is repairable, if that is your problem.

http://www.gmcmhphotos.com/photos/hvac-dash-and-blower-control/p58077-hvac-control-panel-function-switch.html

Here's the 1976 heater/ac vacuum "schematic"

http://www.gmcmhphotos.com/photos/color-hvac-troubleshooting-charts/p22990-hvac-diagram-color-comp.html

I would check that I got vacuum at the "vacuum tank" (upper right hand corner of the color diagram, physically located on the driver side of the blower box). And go from there.

That URL above for dash control is the electrical stuff. Here's the vacuum stuff

http://gmcmotorhome.info/heat.html#CONTROL

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Re: [GMCnet] Front dash A/C issues [message #319362 is a reply to message #319357]

Tue, 20 June 2017 21:59

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

Usually--- the loss of vacuum is a failed hose in the underhood area due to the harsh environment. Easy to trace. I bet once you have vacuum it works. No vacuum it defaults to DEF for safety readins.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: [GMCnet] Front dash A/C issues [message #319382 is a reply to message #319357]

Wed, 21 June 2017 09:50

BobDunahugh

Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA

Karma: 11

Senior Member

Thanks Gary for the info. But I Think the 78 is different then the 76. ( Note. I think.) And I know that the default is to defrost. But it just has vent only. I need to start pulling covers off. Might be a mouse thing. Let you know. Bob Dunahugh

________________________________
From: Bob Dunahugh
Sent: Tuesday, June 20, 2017 8:22 PM
To: gmclist@list.gmcnet.org
Subject: Front dash A/C issues

Leaky compressor issue solved. I got a Sanden compressor from Applied. Very nice, and simple to install. I flushed it, and put in Oil for R-12. ( got lots of R-12 ) Replaced all electrical components. Now that all works nicely. Next the vacuum components. Nothing works. Is the major problem generally the vacuum valve in the dash control? Then there's the 5 I think diaphragms. It's a 1978 GMC. Bob Dunahugh
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Re: [GMCnet] Front dash A/C issues [message #319383 is a reply to message #319382]

Wed, 21 June 2017 09:58

James Hupy

Messages: 6806
Registered: May 2010

Karma: -62

Senior Member

Bob, the vacuum motors open and close flappers in the ducting. On the edges
of the flaps, there was originally a felt like piece of material that
closed off the ducts. Probably make really good mouse nesting materials. My
guess anyway. They are kind of a bugger to get to, but a hand vacuum pump
can easily test the dash pots to see if the diaphragms will still move and
hold the flappers. Stuff never ends, does it?
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Jun 21, 2017 7:51 AM, "Bob Dunahugh" wrote:

> Thanks Gary for the info. But I Think the 78 is different then the 76. (
> Note. I think.) And I know that the default is to defrost. But it just has
> vent only. I need to start pulling covers off. Might be a mouse thing. Let
> you know. Bob Dunahugh
>
>
> ________________________________
> From: Bob Dunahugh
> Sent: Tuesday, June 20, 2017 8:22 PM
> To: gmclist@list.gmcnet.org
> Subject: Front dash A/C issues
>
>
> Leaky compressor issue solved. I got a Sanden compressor from Applied.
> Very nice, and simple to install. I flushed it, and put in Oil for R-12. (
> got lots of R-12 ) Replaced all electrical components. Now that all works
> nicely. Next the vacuum components. Nothing works. Is the major problem
> generally the vacuum valve in the dash control? Then there's the 5 I
> think diaphragms. It's a 1978 GMC. Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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