Home » Public Forums » GMCnet » HVAC air flow questions 77 model (No heat from floor vents)
| HVAC air flow questions 77 model [message #267225] |
Sat, 06 December 2014 07:25  |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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I've spent a couple hours this morning searching and reading about HVAC systems and haven't found the answer to my question...actually two questions.
I have a late 77 with one of the less sucky HVAC units. I have good (by GMC standards) air flow from the AC vents but no detectable air flow on the floor when in heat mode. All the air comes out the AC vents and your feet freeze. We're planning on going to the Lazy Days rally in Tampa next month and I would like to get some heat on the floor.
First question: Is this just the nature of the beast or is there an air door or valve that is not working? If so, any ideas on how to reach it or where it is? Thoughts, advice, and opinions welcome.
Second question: Under the hood center is a plastic flap and under that is what appears to be a fresh air intake. I have not yet investigated if the air door in it is working or not. We rarely use anything but max air and in the very unlikely event it gets too cold, just adjust via adding some heat. Is there anything to be gained/lost by sealing this area up?
I'm not yet ready to gut my dash so if there is anything I can do to improve things, I'm open.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: HVAC air flow questions 77 model [message #267229 is a reply to message #267225] |
Sat, 06 December 2014 08:15  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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kerry pinkerton wrote on Sat, 06 December 2014 06:25I've spent a couple hours this morning searching and reading about HVAC systems and haven't found the answer to my question...actually two questions.
I have a late 77 with one of the less sucky HVAC units. I have good (by GMC standards) air flow from the AC vents but no detectable air flow on the floor when in heat mode. All the air comes out the AC vents and your feet freeze. We're planning on going to the Lazy Days rally in Tampa next month and I would like to get some heat on the floor.
First question: Is this just the nature of the beast or is there an air door or valve that is not working? If so, any ideas on how to reach it or where it is? Thoughts, advice, and opinions welcome.
Second question: Under the hood center is a plastic flap and under that is what appears to be a fresh air intake. I have not yet investigated if the air door in it is working or not. We rarely use anything but max air and in the very unlikely event it gets too cold, just adjust via adding some heat. Is there anything to be gained/lost by sealing this area up?
I'm not yet ready to gut my dash so if there is anything I can do to improve things, I'm open.
Kerry, that last gen HVAC system is actually pretty effective when everything works right. It sounds like you have sticky doors and or low vacuum if any to the doors. One of the most easily accessible doors is the recirc door that you can reach from the inside at floor level just to the right of centerline. I would cycle the AC control from max to normal with the blower on full and see or listen if that door opens and closes. If it does, you have vacuum and a control unit that is not leaking excessivley. If that door doesn't move you should reach in the hole and move it by hand to see if it moves freely. If it does, you probably don't have vacuum in the system due to several issues. If the recirc door works, then you probably have a stuck mode door. This is very common and many times can be fixed just by repeatedly cycling the mode lever from AC to heater to defrost. Let the system run in each mode for a few minutes with the emgine idling and the blower on low. It may gradually loosen up and move--works for me every time after sitting. That's a start and depending on what happens, there are a lot more things to check and do.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: HVAC air flow questions 77 model [message #267231 is a reply to message #267225] |
Sat, 06 December 2014 08:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The foam seals on the air doors turns to sticky goo and does what Kerry said. Mine all work correctly thankfully on my 77. I would not circumvent the recirc door as designed. You don't want rec in vent (it's not vent then is it) or heat or def or you will steam up inside. Check the vac supply hoses starting at the engine for cracks and splits. I find the ones under dash are more protected from heat and combustion byproducts and usually are still pliable.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: HVAC air flow questions 77 model [message #267405 is a reply to message #267225] |
Wed, 10 December 2014 16:55 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Well apparently I had a stuck door or something. It's working now AND, the vacuum gauge I have on my brake booster is staying at 22 inches. Previously, it would bleed off to 0 in about 10-15 minutes which indicated a leak somewhere.
Not a huge air flow but previously there was none. Has anyone every tried a puller Auxiliary fan to get more floor heat?
Btw, the AC vents blow also when in HEAT mode. Is this normal on a 77 or is that indicative of a door or control problem?
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: HVAC air flow questions 77 model [message #267412 is a reply to message #267405] |
Wed, 10 December 2014 19:39 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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kerry pinkerton wrote on Wed, 10 December 2014 15:55Well apparently I had a stuck door or something. It's working now AND, the vacuum gauge I have on my brake booster is staying at 22 inches. Previously, it would bleed off to 0 in about 10-15 minutes which indicated a leak somewhere.
Not a huge air flow but previously there was none. Has anyone every tried a puller Auxiliary fan to get more floor heat?
Btw, the AC vents blow also when in HEAT mode. Is this normal on a 77 or is that indicative of a door or control problem?
It's not normal and indicates a sticky mode door. Sometimes moving the mode lever through all of the positions including defrost will break it loose.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: HVAC air flow questions 77 model [message #267420 is a reply to message #267225] |
Thu, 11 December 2014 09:24 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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You could have a slight leak at the waffer selector disc making it go to Bilevel mode which we technicaly don't have. If you can get it apart without breaking the button pin retainer--- go to Ace and get a small tube of plumbers lube. Apply a less than pea sized blob to your finger and put a light film on the plastic valve face to help the rubber labarynth seal better and move better. I think Applied has a new design retainer if yours is crisp. It's safe on plumbing washers so should not attack rubber.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: HVAC air flow questions 77 model [message #267430 is a reply to message #267225] |
Thu, 11 December 2014 17:11 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Senior Member |
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Well, I found my problem...at least I found A problem.
I dug the manual out and was studying the vacuum paths and such. Pulled the dash cover off and pulled out the AC vent by the drivers right knee. I could see the AC door. Using a MityVac, I found the correct vacuum hose and 'sucked'. The vent closed. So that means it's not getting vacuum. Before I pull apart the control to get to the wafer, let's make sure we have vacuum.
Let's see, here is the little plastic reservoir with two lines going up the the dash control and this line goes to the engine....hummm, I don't recall seeing that hose connected anywhere on the engine....hummm
Sure enough the little tiny vacuum hose is cut/broken just past the alternator. I'll get vacuum on it tomorrow and see how things work. It certainly won't work without vacuum to the control.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: HVAC air flow questions 77 model [message #267434 is a reply to message #267430] |
Thu, 11 December 2014 19:23 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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kerry pinkerton wrote on Thu, 11 December 2014 16:11Well, I found my problem...at least I found A problem.
I dug the manual out and was studying the vacuum paths and such. Pulled the dash cover off and pulled out the AC vent by the drivers right knee. I could see the AC door. Using a MityVac, I found the correct vacuum hose and 'sucked'. The vent closed. So that means it's not getting vacuum. Before I pull apart the control to get to the wafer, let's make sure we have vacuum.
Let's see, here is the little plastic reservoir with two lines going up the the dash control and this line goes to the engine....hummm, I don't recall seeing that hose connected anywhere on the engine....hummm
Sure enough the little tiny vacuum hose is cut/broken just past the alternator. I'll get vacuum on it tomorrow and see how things work. It certainly won't work without vacuum to the control.
The system is designed to move to the defroster position if there is no vacuum so I still think you have a stuck or sticking mode door
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] HVAC air flow questions 77 model [message #267440 is a reply to message #267439] |
Thu, 11 December 2014 21:51 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Wayne,
Harbor Freight has a shrink tube that is for marine electrics:
http://www.harborfreight.com/42-piece-marine-heat-shrink-tubing-67598.html
This tubing seems to have an ID that has some kind of "stuff" in it that oozes out a bit at the ends when you shrink it.
I reckon it is really good for connections that are exposed to the weather.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Wayne Newland
Sent: Friday, December 12, 2014 2:45 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] HVAC air flow questions 77 model
Shrink wrap?
Wayne Newland F9300 75 Palm Beach Sebastian, Fl
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] HVAC air flow questions 77 model [message #267442 is a reply to message #267440] |
Thu, 11 December 2014 23:19 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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I just use very small rubber vacuum or windshield washer hose to repair that tubing. 1/16 or maybe 3/32 inside diameter. When it's almost impossible to get on the line, that's the right size. Hit the inside of the hose with a shot of silicone spray and stick it on the tubing about an inch and a half and do the same for the other side and you're done. Within a few minutes, the hose won't come off unless you PUSH it off.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] HVAC air flow questions 77 model [message #267459 is a reply to message #267442] |
Fri, 12 December 2014 09:13 |
powerjon
Messages: 2446
Registered: January 2004
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I would avoid using any silicone based spray on any of the vacuum system lines or anything else. Use only petroleum based lubricants. The silicone based lubricants could poison your O2 sensor if you have one in your system. I would also not use “Plumbers Lube” to Lube the disk surface in the heater control unit either as the Plumbers Lube is also a silicone based lube. The most common used lubricant for the heater control is White Grease Lubricant and I use Lubriplate Spray Lube ‘A’ which is a white lithium based lubricant that contains no silicone.
and
or
and
http://tinyurl.com/laa8gne
Or use White lithium in the tube which is available at the big box stores. Do be careful as there are some White grease mixed with a silicone based.
and
http://tinyurl.com/krecefw
My rule of thumb is that I do not use any silicone based sprays on any systems that are connected to the engine. I run a MPFI system and would prefer not to take a chance on poisoning my O2 sensor. You can do what you want, but I prefer not to screw things up using the incorrect stuff.
JR Wright
78 Buskirk Stretch
75 Avion
Michigan
> On Dec 12, 2014, at 12:20 AM, Terry wrote:
>
> I just use very small rubber vacuum or windshield washer hose to repair that tubing. 1/16 or maybe 3/32 inside diameter. When it's almost impossible
> to get on the line, that's the right size. Hit the inside of the hose with a shot of silicone spray and stick it on the tubing about an inch and a
> half and do the same for the other side and you're done. Within a few minutes, the hose won't come off unless you PUSH it off.
> --
> Terry Kelpien
> ASE Master Technician
> 73 Glacier 260
> Smithfield, Va.
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] HVAC air flow questions 77 model [message #267465 is a reply to message #267459] |
Fri, 12 December 2014 10:10 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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And silicone is persistent enough to pollute a subsequent owner's O2 sensor
years hence.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Fri, Dec 12, 2014 at 10:13 AM, John Wright
wrote:
>
> I would avoid using any silicone based spray on any of the vacuum system
> lines or anything else. Use only petroleum based lubricants. The silicone
> based lubricants could poison your O2 sensor if you have one in your
> system. I would also not use “Plumbers Lube” to Lube the disk surface in
> the heater control unit either as the Plumbers Lube is also a silicone
> based lube. The most common used lubricant for the heater control is White
> Grease Lubricant and I use Lubriplate Spray Lube ‘A’ which is a white
> lithium based lubricant that contains no silicone.
> ...
>
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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] HVAC air flow questions 77 model [message #267478 is a reply to message #267438] |
Fri, 12 December 2014 17:09 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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bdub wrote on Thu, 11 December 2014 21:24Sure. Its a little rubber connector on the HELP rack.
I drove up to visit a metal shaping friend and spent the day drooling over the 20 million + in cars in his shop. On the way back I stopped and found the rigid hose on the HELP rack and then found a rubber vacuum line that I could PUSH over it. Should work fine. I'll hook it up tomorrow.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: [GMCnet] HVAC air flow questions 77 model [message #267492 is a reply to message #267478] |
Fri, 12 December 2014 23:28 |
Bullitthead
Messages: 1411
Registered: November 2013
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Have never used enough silicone spray to contaminate any oxygen sensors since they started putting them on vehicles. Not gonna happen. Have used it over a thousand times to lubricate air intake hoses for reassembly. NEVER corrupted an oxygen sensor. Think about the volume of exhaust gas passing that sensor. Think about all the microscopic leftover particles coming out of the fuel oxidation process. Think about how much silica dust is in the air surrounding this planet, that you and your engine breathe. The spritz required to lube a hose to put it on is inconsequential. Do not spray half a can down the intake! Do not spray the oxygen sensor with ANYTHING. The most common cause of sensor failure is contamination from the OUTSIDE, where the wires enter. Water splashed up from the road, antifreeze leaks and cooling system failures. Oil and ATF leaks and spills.
Petroleum based lubricants will react with and degrade rubber based hoses, belts, and tires. If you lube a hose with any kind of grease, it will come off easier than it went on.
And you CAN ask me how I know these things, and I'll tell you, but I'm not gonna type it all out. Only in person or on a hardwired phone.
This stuff is just common sense with mechanical devices, not evil software that stops functioning with one erroneous bit out of several billion.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] HVAC air flow questions 77 model [message #267497 is a reply to message #267492] |
Sat, 13 December 2014 00:10 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Terry,
I just did a search of the internet and this is one of those subjects that goes on and on ad infinitum with people on both sides of
the argument.
Do you think it's OK to coat an intake manifold with sealant that is not O2 sensor compatible?
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Terry
Have never used enough silicone spray to contaminate any oxygen sensors since they started putting them on vehicles. Not gonna
happen. Have used it over a thousand times to lubricate air intake hoses for reassembly. NEVER corrupted an oxygen sensor. Think
about the volume of exhaust gas passing that sensor. Think about all the microscopic leftover particles coming out of the fuel
oxidation process. Think about how much silica dust is in the air surrounding this planet that you and your engine breathe. The
spritz required to lube a hose to put it on is inconsequential. Do not spray half a can down the intake! Do not spray the oxygen
sensor with ANYTHING. The most common cause of sensor failure is contamination from the OUTSIDE, where the wires enter. Water
splashed up from the road, antifreeze leaks and cooling system failures. Oil and ATF leaks and spills.
Petroleum based lubricants will react with and degrade rubber based hoses, belts, and tires. If you lube a hose with any kind of
grease, it will come off easier than it went on.
And you CAN ask me how I know these things, and I'll tell you, but I'm not gonna type it all out. Only in person or on a
hardwired phone.
This stuff is just common sense with mechanical devices, not evil software that stops functioning with one erroneous bit out of
several billion.
--
Terry
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GMCnet mailing list
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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