Neely --
Doesn't sound like factory issue. Sounds more like units we use in the
bucket of a utility truck to keep from freezing to death in the winter.
Basically, it's a small heater core with a fan that blows air. They let you
half freeze to death instead of all the way.
Your dash mount control has a "heater" setting that will put the output of
the dash heater core out at the floor level. Someone on the list will direct
you to the resource for repairs, which can get a little involved.
If yours doesn't switch the fan output to the floor (heater outlets) like a
regular GM car or truck, then the most likely cause is that someone has
disconnected the vacuum supply to the 'programmer', the other name for the
dash control. Start the engine, let it warm up enough to not be on fast
idle.
Turn the fan switch to low. Slowly move the top lever from off to defrost.
You should hear the hissing of vacuum as the programmer steps through the
various settings of the air control doors. The fast test is to cram it to
defrost and flip the fan to high. Air should be shooting out of the dash top
defroster vents with a force you can feel. If it isn't, then either the
programmer is shot or doesn't have a source of vacuum. It's not common for a
GM to have the air control door activators (bellows) fail, but the hoses can
turn to dried earth worms and fall completely off!
All GMC's have massive, bone chilling cold air leaks through the outer shell
into the passenger compartment. It was a regular production option (RPO).
(Unless someone caulked the joints outside or Jim Bounds made it atomic
reactor core tight.) [Just kidding to see if anyone's awake.]
They've got a heck of a strong heater that doesn't do to bad a job if:
1). The heater core isn't full of leak-stop, sometimes called 'dog-s@$*' to
those in the know.
2). The vacuum operated heater core water control valve isn't rusted in the
off position.
3). The programmer is totally shot.
4). A heater hose is pinched shut or collapsed inside.
5). You have a good, working 195 degree thermostat in the engine.
6). And especially in your case, someone hasn't put in another heater and
disconnected the original one because it leaked or didn't work.
See if you can find someone in your area with some experience working on GM
car heater systems, preferably a Buick, Olds, Pontiac or Cadillac. They were
all very similar to the GMC. Chevy's and most trucks were mechanical rather
than vacuum operated.
Hopefully, these ideas will take you a long way toward solving your mystery
of no heat.
> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto
wner-gmcmotorhome]On Behalf Of Neely Butler
> Sent: Tuesday, November 24, 1998 8:02 PM
> To: GMC chat
> Subject: GMC: Heater
>
>
> On my "new" 1978 ELEGANZA II is what previous owner called a "box
> heater" he
> thinks was installed by original owner. He said that it started blowing
> fuses so he quit using it several years ago. All heat now comes from the
> in-dash air-conditioning vents, no way to direct heat to come from floor.
> The "box" is installed under the steering column beneath the floor
> accessible from the left hood door. It has four openings, air
> hoses clamped
> to two go to floor vents, two other openings have been sealed. Another
> opening has a slightly larger hose attached that just hangs
> loose. Beneath
> the instrument panel is a blue light and a rotating switch. Is anyone
> familiar with such a heater, and can you give me any information
> as to where
> loose hose should be attached and wiring information??
> Thanks
> Neely B.
> Tenn
>
Doesn't sound like factory issue. Sounds more like units we use in the
bucket of a utility truck to keep from freezing to death in the winter.
Basically, it's a small heater core with a fan that blows air. They let you
half freeze to death instead of all the way.
Your dash mount control has a "heater" setting that will put the output of
the dash heater core out at the floor level. Someone on the list will direct
you to the resource for repairs, which can get a little involved.
If yours doesn't switch the fan output to the floor (heater outlets) like a
regular GM car or truck, then the most likely cause is that someone has
disconnected the vacuum supply to the 'programmer', the other name for the
dash control. Start the engine, let it warm up enough to not be on fast
idle.
Turn the fan switch to low. Slowly move the top lever from off to defrost.
You should hear the hissing of vacuum as the programmer steps through the
various settings of the air control doors. The fast test is to cram it to
defrost and flip the fan to high. Air should be shooting out of the dash top
defroster vents with a force you can feel. If it isn't, then either the
programmer is shot or doesn't have a source of vacuum. It's not common for a
GM to have the air control door activators (bellows) fail, but the hoses can
turn to dried earth worms and fall completely off!
All GMC's have massive, bone chilling cold air leaks through the outer shell
into the passenger compartment. It was a regular production option (RPO).
(Unless someone caulked the joints outside or Jim Bounds made it atomic
reactor core tight.) [Just kidding to see if anyone's awake.]
They've got a heck of a strong heater that doesn't do to bad a job if:
1). The heater core isn't full of leak-stop, sometimes called 'dog-s@$*' to
those in the know.
2). The vacuum operated heater core water control valve isn't rusted in the
off position.
3). The programmer is totally shot.
4). A heater hose is pinched shut or collapsed inside.
5). You have a good, working 195 degree thermostat in the engine.
6). And especially in your case, someone hasn't put in another heater and
disconnected the original one because it leaked or didn't work.
See if you can find someone in your area with some experience working on GM
car heater systems, preferably a Buick, Olds, Pontiac or Cadillac. They were
all very similar to the GMC. Chevy's and most trucks were mechanical rather
than vacuum operated.
Hopefully, these ideas will take you a long way toward solving your mystery
of no heat.
> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto
wner-gmcmotorhome]On Behalf Of Neely Butler> Sent: Tuesday, November 24, 1998 8:02 PM
> To: GMC chat
> Subject: GMC: Heater
>
>
> On my "new" 1978 ELEGANZA II is what previous owner called a "box
> heater" he
> thinks was installed by original owner. He said that it started blowing
> fuses so he quit using it several years ago. All heat now comes from the
> in-dash air-conditioning vents, no way to direct heat to come from floor.
> The "box" is installed under the steering column beneath the floor
> accessible from the left hood door. It has four openings, air
> hoses clamped
> to two go to floor vents, two other openings have been sealed. Another
> opening has a slightly larger hose attached that just hangs
> loose. Beneath
> the instrument panel is a blue light and a rotating switch. Is anyone
> familiar with such a heater, and can you give me any information
> as to where
> loose hose should be attached and wiring information??
> Thanks
> Neely B.
> Tenn
>
