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AC Question [message #303653]

Sat, 16 July 2016 12:29

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

During the process of trying to replace the blower motor on my dash air, I discovered that my '75 coach has the recirc door in the blower housing that, according to Zay Brand, is typical on '73 & '74 models. I tried operating the vacuum servo with a vacuum pump, and it did work. However, it does nothing with the coach running (17 - 18" vacuum) and the AC on. I looked over the controls behind the dash and didn't spot anything amiss there.

I am wondering if anyone has any pointers on a. - how to fix it properly so it works the way it should, or b. - if it is a good idea to pull that door up into the recirc position and put a screw in it to keep it there. That way, according to Zay Brand's essay, I will get 80% recirc on the AC instead of 100% outside air.

Maybe my coach has a '74 dash air unit. The SN is TZE 165V101455, so it's not really an early '75 coach, but it has the full length body pads like the earlier coaches had. This might explain why the blower motor I got from Applied didn't fit (goes in the hole too far). I blew out the old motor and lubed it up and it will have to do until we can straighten out the motor issue.

Thanks

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

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Re: AC Question [message #303654 is a reply to message #303653]

Sat, 16 July 2016 13:00

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Carl S. wrote on Sat, 16 July 2016 12:29

During the process of trying to replace the blower motor on my dash air, I discovered that my '75 coach has the recirc door in the blower housing that, according to Zay Brand, is typical on '73 & '74 models. I tried operating the vacuum servo with a vacuum pump, and it did work. However, it does nothing with the coach running (17 - 18" vacuum) and the AC on. I looked over the controls behind the dash and didn't spot anything amiss there.

I am wondering if anyone has any pointers on a. - how to fix it properly so it works the way it should, or b. - if it is a good idea to pull that door up into the recirc position and put a screw in it to keep it there. That way, according to Zay Brand's essay, I will get 80% recirc on the AC instead of 100% outside air.

Maybe my coach has a '74 dash air unit. The SN is TZE 165V101455, so it's not really an early '75 coach, but it has the full length body pads like the earlier coaches had. This might explain why the blower motor I got from Applied didn't fit (goes in the hole too far). I blew out the old motor and lubed it up and it will have to do until we can straighten out the motor issue.

Thanks

You need to check the vacuum lines to the accumulator and from there to the dash control and from the dash control to the actuator for plugs and leaks.

http://www.gmcmhphotos.com/photos/data/4858/HVAC_Diagram_--_Color_Comp.jpg

Assuming you have an additional, manually operated, hardware store shut-off valve in the line to the heater core (the OEM vacuum operated one is prone to not shutting all the way off), you need to open up the blower box and install the diverter that Zay Brand recommends, and replace the foam "weather-stripping" on both the recirc door and the temperature door. You could also install an external cover on the recirc opening like Zay suggests.

You can clean all the dirt and stuff out of the evaporator core while you have the blower box cover off.

To really get some cold air to the cabin, you need to run your own vent plumbing from the cold side of the evaporator to the cabin. There are a couple of examples on the photo site.

[Updated on: Sat, 16 July 2016 13:08]

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Re: AC Question [message #303656 is a reply to message #303653]

Sat, 16 July 2016 13:11

wally

Messages: 643
Registered: August 2004
Location: Omaha Nebraska

Karma: 5

Senior Member

Carl S. wrote on Sat, 16 July 2016 12:29

During the process of trying to replace the blower motor on my dash air, I discovered that my '75 coach has the recirc door in the blower housing that, according to Zay Brand, is typical on '73 & '74 models. I tried operating the vacuum servo with a vacuum pump, and it did work. However, it does nothing with the coach running (17 - 18" vacuum) and the AC on. I looked over the controls behind the dash and didn't spot anything amiss there.

I am wondering if anyone has any pointers on a. - how to fix it properly so it works the way it should, or b. - if it is a good idea to pull that door up into the recirc position and put a screw in it to keep it there. That way, according to Zay Brand's essay, I will get 80% recirc on the AC instead of 100% outside air.

Maybe my coach has a '74 dash air unit. The SN is TZE 165V101455, so it's not really an early '75 coach, but it has the full length body pads like the earlier coaches had. This might explain why the blower motor I got from Applied didn't fit (goes in the hole too far). I blew out the old motor and lubed it up and it will have to do until we can straighten out the motor issue.

Thanks

Ken Henderson posted this on vacuum servos
http://www.gmcmhphotos.com/photos/color-hvac-troubleshooting-charts/p22990-hvac-diagram-color-comp.html
http://www.gmcmhphotos.com/photos/color-hvac-troubleshooting-charts/p22988-hvac-connection-charts-color-comp.html
Out coach SN 165v100704 did not have the recirc door and did have the "air horn" under the dash. What was supposed to be the recirc servo was connected to a damper on the air horn. I found and installed a OEM recirc door and cut the dash so it would work using the servo. AC works way better with recirc. The air horn damper has a manual lever to actuate it now.

Wally Anderson
Omaha NE
75 Glenbrook

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Re: [GMCnet] AC Question [message #303657 is a reply to message #303653]

Sat, 16 July 2016 13:34

emerystora

Messages: 4442
Registered: January 2004

Karma: 13

Senior Member

I would definitely block the recirc flapper to keep it open all the time. You should also cover the opening where outside air enters the blower housing from the front. This will help keep warm air from being sucked into the coach.

Your heater control has a rubber disk between two plastic disks. This has grooves which direct the vacuum to the proper heater flappers depending on the position of the lever. The disk is likely leaking. There is a plastic pin in the center that holds it tight. If the pin is broken it will be loose and leaking. Alex Sirim GMC in Florida makes a new metal pin.

If the pin is ok the disk might be worn. There is no replacement that has the right grooves that the GMC needs. You can clean the disk by using some valve grinding compound of a flat piece of glass. Polishing the disk should stop the leaking.

Also be sure to check that you are getting vacuum to the heater controls when the engine is robbing. You could have a loose or cracked vacuum line.

Emery Stora
77 Kingsley
Frederick, CO

> On Jul 16, 2016, at 11:29 AM, Carl Stouffer wrote:
>
> During the process of trying to replace the blower motor on my dash air, I discovered that my '75 coach has the recirc door in the blower housing
> that, according to Zay Brand, is typical on '73 & '74 models. I tried operating the vacuum servo with a vacuum pump, and it did work. However, it
> does nothing with the coach running (17 - 18" vacuum) and the AC on. I looked over the controls behind the dash and didn't spot anything amiss
> there.
>
> I am wondering if anyone has any pointers on a. - how to fix it properly so it works the way it should, or b. - if it is a good idea to pull that door
> up into the recirc position and put a screw in it to keep it there. That way, according to Zay Brand's essay, I will get 80% recirc on the AC instead
> of 100% outside air.
>
> Maybe my coach has a '74 dash air unit. The SN is TZE 165V101455, so it's not really an early '75 coach, but it has the full length body pads like
> the earlier coaches had. This might explain why the blower motor I got from Applied didn't fit (goes in the hole too far). I blew out the old motor
> and lubed it up and it will have to do until we can straighten out the motor issue.
>
> Thanks
>
>
> --
> 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

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Re: [GMCnet] AC Question [message #303659 is a reply to message #303657]

Sat, 16 July 2016 15:28

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

Fixed! Upon double checking, I did indeed have a cracked vacuum line, the purple one in the three line manifold at the top left on the control. I cut that line out of the connector and spliced the purple line in with a short length of rubber hose. Now the recirc door closes just like it's supposed to.

I'll let it go like that for now and see how much of a difference it makes. I might do some of the other modifications when I am feeling more ambitious and it's not 105 outside.

I had already repaired the broken plastic pin in the control several years ago and evidently the rest of the AC control panel works as it should.

Thanks for all the help and suggestions.

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Re: AC Question [message #303661 is a reply to message #303653]

Sat, 16 July 2016 16:29

JohnL455

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

Karma: 12

Senior Member

Now that it works leave it alone. If you rig the door to the recirc position then VENT is just recirc and not vent. And in heat and def positions you need to have 100% outside air to prevent fogging inside.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: [GMCnet] AC Question [message #303662 is a reply to message #303661]

Sat, 16 July 2016 16:37

emerystora

Messages: 4442
Registered: January 2004

Karma: 13

Senior Member

John
I have never had a problem with fogging inside and I have completely closed off the outside air intake.
It has been this way for at least 15 years now. Its cooler with the air conditioning on and warmer in the winter.

The GMC motorhomes have enough leaks of outside air that I have never seen the need for the Vent position.

Emery Stora
77 Kingsley
Frederick, CO

> On Jul 16, 2016, at 3:30 PM, John R. Lebetski wrote:
>
> Now that it works leave it alone. If you rig the door to the recirc position then VENT is just recirc and not vent. And in heat and def positions
> you need to have 100% outside air to prevent fogging inside.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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Re: [GMCnet] AC Question [message #303666 is a reply to message #303662]

Sat, 16 July 2016 17:15

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

I'll probably just leave it, now that it's working right. I kind of like the idea of having some outside air coming in to keep a little positive pressure in the coach.

Who'd a thunk it would still work as designed after all these years. I guess I should have looked at it a little harder years ago. Small steps toward getting the air conditioning working better.

[Updated on: Sun, 17 July 2016 09:20]

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Re: [GMCnet] AC Question [message #303667 is a reply to message #303666]

Sat, 16 July 2016 17:24

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Carl S. wrote on Sat, 16 July 2016 17:15

I'll probably just leave it, now that it's working right. I kind of like the idea of having some outside air coming in to keep a little positive pressure in the coach.

Who'd a thunk it would still work as designed after all these years. I guess I should have looked at it a little harder years ago. Small steps toward getting the air conditioning working

Do you have the hardware store valve in the line to the heater core to make sure there is no hot coolant flowing through it when you want air conditioning?

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Re: [GMCnet] AC Question [message #303669 is a reply to message #303667]

Sat, 16 July 2016 17:49

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

A Hamilto wrote on Sat, 16 July 2016 15:24

Carl S. wrote on Sat, 16 July 2016 17:15
I'll probably just leave it, now that it's working right. I kind of like the idea of having some outside air coming in to keep a little positive pressure in the coach.

Who'd a thunk it would still work as designed after all these years. I guess I should have looked at it a little harder years ago. Small steps toward getting the air conditioning working
Do you have the hardware store valve in the line to the heater core to make sure there is no hot coolant flowing through it when you want air conditioning?

Yes, I've had that for 8 years. It really does make a difference. The vacuum operated valve evidently does seem to allow a little hot water through. The problem with the ball valve in the heater hose is that we sometimes need the heat in the morning and the AC a little later in the day. With 30 to 40 degree temperature swings sometimes I forget to change it over.

[Updated on: Sat, 16 July 2016 18:54]

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Re: AC Question [message #303670 is a reply to message #303653]

Sat, 16 July 2016 18:12

JohnL455

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

Karma: 12

Senior Member

Emery with my chemical issues I like having fresh air constantly coming in and changing out the air in the coach. The slight positve pressure makes leak leak "out" along with CO and holding tank odors. Wes did a writeup on this in one of the the old newsletters FWIW. If it gets realy hot I can go to REC for a while and yes it helps to have 80 deg air hitting the evaporator as opposed to 100 deg air. Glad I have a 77 w R12 that holds charge really well.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: AC Question [message #303672 is a reply to message #303670]

Sat, 16 July 2016 19:02

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

On a somewhat related note;

Ever since we've had this coach, the rear AC unit has been somewhat persnickety, sometimes not wanting to start and just sitting there on the roof humming, or sometimes shutting it's self down when running on low speed. I have had to climb up the roof ladder and poke the fan with a stick to get it to run. I even entertained thoughts of replacing the motor early on, thinking it was just weak. Even lubricating the bearings didn't seem to help.

While adding a second solar panel last week, I had the cover off the unit to mount the panel to it, and saw that the ground connection to the motor looked loose. I took it apart and cleaned it all up, and put it back together tight. Today, I turned on the unit and it started up right away, no problem. Hope that did the trick. Time will tell.

[Updated on: Sat, 16 July 2016 20:08]

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Re: [GMCnet] AC Question [message #303674 is a reply to message #303672]

Sat, 16 July 2016 19:26

James Hupy

Messages: 6806
Registered: May 2010

Karma: -62

Senior Member

Open the window, stick your head out like the dog does. (Grin)
Jim Hupy
On Jul 16, 2016 5:03 PM, "Carl Stouffer" wrote:

> On a somewhat related note;
>
> Ever since we've had this coach, the rear AC unit has been somewhat
> persnickety, sometimes not wanting to start and just sitting there on the
> roof
> humming, or sometimes shutting it's self down when running on low speed.
> I have had to climb up the roof ladder and poke the fan with a stick to get
> it to run. I even entertained thoughts of replacing the motor early on,
> thinking it was just weak. Even lubricating the bearings didn't seem to
> help.
>
> While adding a second solar panel last week, I had the cover off the unit
> to mount the panel to it, and saw that the groung connection to the motor
> looked loose. I took it apart and cleaned it all up, and put it back
> together tight. Today, I turned on the unit and it started up right away,
> no
> problem. Hope that did the trick. Time will tell.
> --
> 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Re: [GMCnet] AC Question [message #303680 is a reply to message #303674]

Sat, 16 July 2016 21:41

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

James Hupy wrote on Sat, 16 July 2016 17:26

Open the window, stick your head out like the dog does. (Grin)
Jim Hupy

Kind of get the same effect with the toll windows open and the wind wings in the 'scoop' position. Laughing

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