Home » Public Forums » GMCnet » Need help with cabin heat ASAP (solved for now)
| Need help with cabin heat ASAP (solved for now) [message #340665] |
Tue, 05 February 2019 22:48  |
NextGenGMC
Messages: 146
Registered: December 2017
Location: Washington State
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Hello fellow GMC'rs,
I need help and I need advice regarding cabin heat. I have a trip coming up in a few days. The temps outside have dropped, not like in the mid-west but still cold, and my cabin heat stopped working. I had some issues with it before, but I thought I had it solved with re-connecting all the vacuum lines on the controller unit.
Right now I have the fan blowing, but not getting any heat at all - just cold air. I found out that my vacuum valve on the line to the heater core was not operating (not getting any vacuum). I put a zip-tie on it to keep it in fully open position. This allowed fluid flow and it actually produced heat in the cabin but only to the center outlet. Also, when controls were in the DEFROST position, I was also getting warm air delivered to the windshield. That sounds great and I though I had the issue solved... Unfortunately, after playing with controls some more, the heat stopped completely. The valve is still in OPEN position, the heater blend door seem to be in proper position for heat (lever position on the box does change when I switch from COLD to HOT). I do have vacuum feed to the vacuum canister (about -16-17 in Hg) and out of the canister and to the controller in the cab (about -15 in Hg). I'm getting vacuum to some of the selector valves (center one on defrost and the one on the passenger side for sure).
What am I missing and what can be causing the lack of heat?
One thing that puzzles me is this: the rubber hose going to the heater box warm past the vacuum valve (not hot, just warm). However, return hose coming out of the box is ice cold. If I touch the same outlet hose further down, closer to the radiator, - it is as warm as the Input hose. Could my heater core be completely plugged and not allowing coolant circulation at all? What else do I need to look for?
Any advice is appreciated. For this trip I might have to bundle up in blankets  but still need to get this solved eventually. Especially because I can tolerate cold temps much better than my significant other 
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
[Updated on: Wed, 06 February 2019 11:09] Report message to a moderator |
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| Re: Need help with cabin heat ASAP [message #340670 is a reply to message #340665] |
Tue, 05 February 2019 23:40  |
JohnS
Messages: 126
Registered: December 2014
Location: Vacaville, CA
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I might try bypassing that water valve. The fact that you have feel warm but not hot past the valve suggests a restriction at that point. if that does not help, I would suspect a plugged heater core.
Hoping for a bad valve! John S.
John Shutzbaugh, Vacaville, CA, ncserv@aol.com;
78 Buskirk stretch, "What were we thinking?"
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| Re: Need help with cabin heat ASAP [message #340672 is a reply to message #340670] |
Wed, 06 February 2019 00:31 |
NextGenGMC
Messages: 146
Registered: December 2017
Location: Washington State
Karma: -1
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JohnS wrote on Tue, 05 February 2019 21:40I might try bypassing that water valve. The fact that you have feel warm but not hot past the valve suggests a restriction at that point. if that does not help, I would suspect a plugged heater core.
Hoping for a bad valve! John S.
Question - is this valve in CLOSED or OPENED flow position when vacuum is not supplied to it?
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
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| Re: Need help with cabin heat ASAP [message #340675 is a reply to message #340674] |
Wed, 06 February 2019 08:02 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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JohnL455 wrote on Wed, 06 February 2019 08:45The 2 GM defaults are
No vacuum to valve = OPEN
No vacuum to selectorr doors= DEF
Both for saftey reasons.
Vadim,
John is correct. But, what has not been said is that the vacuum controlled valve can fail in a mid-position such that even if you were to wire it so the visible operating arm was in the open position, it still might not actually be wide open. The Warm/Cold lines you are finding would suggest that you have this issue.
It also could be that the heater core is air-bound. Have you had the coach out for an extended highway run with the heater on since the last coolant service. This happened to me, and we were uncomfortable until - Blast of Heat - then we were uncomfortable again until I got it shut down.
Your heat "only out the center defrost" also sounds a like so many little vacuum leaks. There is no easy way to diagnose this, just inspect every little vacuum line that you can find. If you are lucky (as I was), you might just find one little rubber line cracked where it connects to an operator.
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
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| Re: Need help with cabin heat ASAP [message #340677 is a reply to message #340665] |
Wed, 06 February 2019 09:22 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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I had a similar issue a few years ago when we REALLY needed the heat. I checked everything and wasn't able to make repairs on the road and we just bundled up and suffered during the rest of the trip. I subsequently back-flushed the heater core with a garden hose and got a lot of dirty looking water out. That solved the problem for me. It sounds like you may have a different issue, but I'm just putting this out there just in case you want to try it.
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: Need help with cabin heat ASAP [message #340678 is a reply to message #340665] |
Wed, 06 February 2019 09:25 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The partial open/ restricted water valve that Matt mentioned, along with low coolant or dirty core can cause warmer air from some vents and colder from others as only part of the core is warm and the air moves in somewhat a linear fashion after leaving the core. I had fairly good heat out of the VENT position and less out of the HEAT position (seems reversed) until all the air worked out of the core. Now it works correctly. Added challenge is the high mounted position of the core relative to the 9 PSI rad cap. Your cap must be 100% as far as both rubber seals and the tiny return poppet spring must close the return valve. This tiny spring fails long before the main pressure spring and is hidden. Also be sure the overflow hose is not aged out and clamps snug if not GM spring type . Hose can look ok and be porous with micro checking. It will duct the coolant to the tank, but can return air instead, lowering the system level instead of replenishing it with each hot/cold cycle
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Need help with cabin heat ASAP [message #340679 is a reply to message #340665] |
Wed, 06 February 2019 09:33 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Also be sure you press down on the cap reinstalling it so it turns to the final position not just to the saftey position. This may be obvious, but more difficult than on a typical pass car due to location.
John Lebetski
Woodstock, IL
77 Eleganza II
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 Re: Need help with cabin heat ASAP [message #340681 is a reply to message #340665] |
Wed, 06 February 2019 11:08 |
NextGenGMC
Messages: 146
Registered: December 2017
Location: Washington State
Karma: -1
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First of all a BIG BIG THANK YOU to everyone for the replies. This forum and this community is truly amazing.
I had a chance to fiddle some more with the system. It turns out the vacuum valve was stuck partially closed. With the bypass - the heat in the cabin works again. Both hoses to and from the heater core are now nice and warm to touch indicating that the coolant is flowing through it. I didn't run the engine for too long, but it was long enough that the heat output to the cabin was noticeable even before the DigiPanel registered the engine temp at the low end. My heat to defrost works too and seems to be uniform across all the windows. When directed to the cabin, I still get heat only to the center outlet. The passenger side might be getting some heat too, but as I said - didn't run the system long enough to confirm it 100%. I'm just glad to have heat at least to the center and to defrost.
Somewhat related question - I have a large floor vent at the center of the cabin (right below where two center outlets working). It seem like that vent is blowing just cold air all the time and blowing it pretty intensely. The flow of air to that outlet does not change at any controller position. Is that an "aftermarket" addition or is it likely to be related to some vacuum controller not working? Is that suppose to be intake for recirculated air? I'm tempted to block off that vent with tape until i have time to explore what all control valves are doing/not doing. Is that a good plan? Is it likely to cause some unintended harm elsewhere?
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
[Updated on: Wed, 06 February 2019 11:11] Report message to a moderator |
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| Re: Need help with cabin heat ASAP [message #340683 is a reply to message #340681] |
Wed, 06 February 2019 11:33 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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That rectangular hole is the recirculate intake. Don't block it off. Stick a flashlight in the opening, go out front under the hood, and look for that light in the outside air intake. I could see right through to the inside on mine, and subsequently blocked the outside off with a sheet of rubber. Duct tape will do on the side of the road. It was a cold ride back from Danville in February when we bought the coach before I fixed that obvious, incredible, design defect.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Need help with cabin heat ASAP (solved for now) [message #340684 is a reply to message #340665] |
Wed, 06 February 2019 12:00 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I thought he was referring to the dual Max AC duct as he has a 76. The recirc door on 77-78 would be sucking not a source of cold draft. Not sure of the rec door location on 76 but might be more pass side.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Need help with cabin heat ASAP (solved for now) [message #340685 is a reply to message #340665] |
Wed, 06 February 2019 12:09 |
tgeiger
Messages: 518
Registered: February 2006
Location: kansas city
Karma: -1
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Senior Member |
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I kinda think I'm experiencing the same thing. Is there a write up or photo power point on how to bypass this? Was hoping to place a inkine gate valve to use for heating in the winter but block off hot water from core for air conditioning in thr summer?
Tom Geiger
76 Eleganza II
KCMO
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| Re: Need help with cabin heat ASAP (solved for now) [message #340688 is a reply to message #340684] |
Wed, 06 February 2019 13:24 |
NextGenGMC
Messages: 146
Registered: December 2017
Location: Washington State
Karma: -1
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JohnL455 wrote on Wed, 06 February 2019 10:00I thought he was referring to the dual Max AC duct as he has a 76. The recirc door on 77-78 would be sucking not a source of cold draft. Not sure of the rec door location on 76 but might be more pass side.
Nope, not Dual Max AC, just a vent opening. I wonder if recirc valve or door is stuck open and I'm getting a blow by from the fan going in the direction opposite to what was intended. Plan on sticking a flashlight in both directions today to explore it.
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
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| Re: [GMCnet] Need help with cabin heat ASAP [message #340689 is a reply to message #340681] |
Wed, 06 February 2019 13:42 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Vadim,
That ~3"x~12 hole in the center of the firewall is the "Max Air Duct". '75
& '76 coaches (Type II air conditioning) came equipped with a plastic duct
which fit into that hole, then lead to 4 louvered outlets below the dash.
I think there was even a retrofit kit for earlier coaches. There should be
flow from there ONLY when the "Max" position is selected on the HVAC
control. If there's always flow, something's wrong with the max air
deflector door in the HVAC box. If you don't have Zay Brand's "Separating
Hot from Cold" booklet from GMCWS.org, you need to get it ASAP.
http://gmcws.org/Tech/air_conditioning/air_conditing.html and
http://www.gmcmhphotos.com/photos/g4637-type-ii-dash-air-condition-modification.html
HTH,
Ken H.
On Wed, Feb 6, 2019 at 12:09 PM Vadim Jitkov wrote:
> First of all a BIG BIG THANK YOU to everyone for the replies. This forum
> and this community is truly amazing.
> I had a chance to fiddle some more with the system. It turns out the
> vacuum valve was stuck partially closed. With the bypass - the heat in the
> cabin works again. Both hoses to and from the heater core are now nice and
> warm to touch indicating that the coolant is flowing through it. I didn't
> run the engine for too long, but it was long enough that the heat output
> to the cabin was noticeable even before the DigiPanel registered the engine
> temp at the low end. My heat to defrost works too and seems to be uniform
> across all the windows. When directed to the cabin, I still get heat only
> to the center outlet. The passenger side might be getting some heat too,
> but as I said - didn't run the system long enough to confirm it 100%. I'm
> just glad to have heat at least to the center and to defrost.
>
> Somewhat related question - I have a large floor vent at the center of the
> cabin (right below where two center outlets working). It seem like that
> vent is blowing just cold air all the time and blowing it pretty
> intensely. The flow of air to that outlet does not change at any controller
> position. Is that an "aftermarket" addition or is it likely to relate to
> come vacuum controller not working? Is that suppose to be intake for
> recirculated air? I'm tempted to block off that vent with tape until i
> have time to explore what all control valves are doing/not doing. Is that a
> good plan? Is it likely to cause some unintended harm elsewhere?
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Need help with cabin heat ASAP [message #340698 is a reply to message #340689] |
Wed, 06 February 2019 22:32 |
NextGenGMC
Messages: 146
Registered: December 2017
Location: Washington State
Karma: -1
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Senior Member |
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Ken Henderson wrote on Wed, 06 February 2019 11:42Vadim,
That ~3"x~12 hole in the center of the firewall is the "Max Air Duct". '75
& '76 coaches (Type II air conditioning) came equipped with a plastic duct
which fit into that hole, then lead to 4 louvered outlets below the dash.
I think there was even a retrofit kit for earlier coaches. There should be
flow from there ONLY when the "Max" position is selected on the HVAC
control. If there's always flow, something's wrong with the max air
deflector door in the HVAC box. If you don't have Zay Brand's "Separating
Hot from Cold" booklet from GMCWS.org, you need to get it ASAP.
http://gmcws.org/Tech/air_conditioning/air_conditing.html and
http://www.gmcmhphotos.com/photos/g4637-type-ii-dash-air-condition-modification.html
HTH,
Ken H.
On Wed, Feb 6, 2019 at 12:09 PM Vadim Jitkov wrote:
> First of all a BIG BIG THANK YOU to everyone for the replies. This forum
> and this community is truly amazing.
> I had a chance to fiddle some more with the system. It turns out the
> vacuum valve was stuck partially closed. With the bypass - the heat in the
> cabin works again. Both hoses to and from the heater core are now nice and
> warm to touch indicating that the coolant is flowing through it. I didn't
> run the engine for too long, but it was long enough that the heat output
> to the cabin was noticeable even before the DigiPanel registered the engine
> temp at the low end. My heat to defrost works too and seems to be uniform
> across all the windows. When directed to the cabin, I still get heat only
> to the center outlet. The passenger side might be getting some heat too,
> but as I said - didn't run the system long enough to confirm it 100%. I'm
> just glad to have heat at least to the center and to defrost.
>
> Somewhat related question - I have a large floor vent at the center of the
> cabin (right below where two center outlets working). It seem like that
> vent is blowing just cold air all the time and blowing it pretty
> intensely. The flow of air to that outlet does not change at any controller
> position. Is that an "aftermarket" addition or is it likely to relate to
> come vacuum controller not working? Is that suppose to be intake for
> recirculated air? I'm tempted to block off that vent with tape until i
> have time to explore what all control valves are doing/not doing. Is that a
> good plan? Is it likely to cause some unintended harm elsewhere?
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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I do in fact have the Type 2 controller system, but the additional outlets have been removed. I only have the 3x12 opening down there. I've checked door operation behind that opening. It does move and operate with the vacuum controller. However, even when fully closed, the air is still blowing past the edges of the door. My guess the door just doesn't seal fully, perhaps need some foam tape there to seat against. With anticipated cold temps during the drive, I've decided to block off that outlet for now. When summer comes, I'll open the heater/cooler box and try to get all things to function as intended. Perhaps with installation of a ball valve on the heater core hose, I'll even get the AC to blow cold air I the summer
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
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| Re: Need help with cabin heat ASAP [message #340699 is a reply to message #340670] |
Wed, 06 February 2019 23:56 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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If you want it is a simple project to just replace that vacuum valve with a ball valve. Last one that I did was on a coach that I was transporting cross country from Salt Lake City in the winter. II had no heat so I went Home Depot and bought a ball valve and swapped the old one out is about 10 minutes in the HD parking lot. It was a one screwdriver project. I delivered the coach to Florida where the owner said "good, I'll turn the ball valve off and be done with it. I'll never need the heat anyway. If I ever do I'll turn the valve back on again."
The Valve is located in the heater hose in the center. It is accessed by opening the driver's side hood. Oh yes, to prevent a vacuum leak, be sure to stick something in the vacuum line like a screw when the old one valve is removed.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Need help with cabin heat ASAP [message #340703 is a reply to message #340698] |
Thu, 07 February 2019 07:49 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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NextGenGMC wrote on Wed, 06 February 2019 23:32I do in fact have the Type 2 controller system, but the additional outlets have been removed. I only have the 3x12 opening down there. I've checked door operation behind that opening. It does move and operate with the vacuum controller. However, even when fully closed, the air is still blowing past the edges of the door. My guess the door just doesn't seal fully, perhaps need some foam tape there to seat against. With anticipated cold temps during the drive, I've decided to block off that outlet for now. When summer comes, I'll open the heater/cooler box and try to get all things to function as intended. Perhaps with installation of a ball valve on the heater core hose, I'll even get the AC to blow cold air I the summer
Vadim,
That door has probably lost the foam cover than it had just a few decades ago. The foam cover was both to seal the doors and as a noise abatement. You can replace it with any soft foam. If you can find really soft self stick foam weather striping, that is what I used and it was effective when I finally got it to stick.
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
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| Re: [GMCnet] Need help with cabin heat ASAP [message #340710 is a reply to message #340703] |
Thu, 07 February 2019 10:47 |
NextGenGMC
Messages: 146
Registered: December 2017
Location: Washington State
Karma: -1
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Senior Member |
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Matt Colie wrote on Thu, 07 February 2019 05:49...
That door has probably lost the foam cover than it had just a few decades ago...
Matt
That is exactly what is going on there. Just bare metal flap at this time.
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
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