> Mark
>
> I have a question for you. You say the air should "shoot out of the dash"
> I would describe mine as crawling out. I first tried this with
> the engine off.
> Well, then I read the engine had to be on so I did that------nothing. Then
> a friend pointed out the high speed relay-------hey changed out
> that puppy.
> That helped got the high speed------but not much more air. Read about
> bad gaskets inside heater box broke it open yeah it was sad. Not to
> mention the darn hornet nest in it. Most of the box was full of a wasp
> nest. Hey I have found the problem-----not! Yes, I have vacuum control
> Got good gaskets and so little air. Any Ideas?
I can only speak from my first hand knowledge of out '77, and I'm not sure
when GM changed the design from 'early' to 'late'. I also had low air flow
when we bought our coach. I did all the things you've done, and these things
too:
1). Replaced all the vacuum hoses that lead to, on and from the dash
programmer (control). They were shot, leaked vacuum and wouldn't operate the
damper doors. There are two primary functions of the air doors, one set that
moves the air flow from heater to the dash to the defroster, and another
that puts the system in recirculate mode for maximum A/C. On our coach, the
recirculate door control mount was bent, so it wouldn't go into MAX mode.
On the GMC, the temp adjust door is operated by a Bowden cable, not vacuum.
I've thought about converting it, but... I just fiddle the setting as
needed. A GM/Harrison Comfortron from that vintage isn't a real pretty
thing.
2). Replaced the high speed +12 supply wiring, which had melted, with a 10ga
wire to carry the current.
3). Put on a new squirrel cage fan. The original one vibrated like crazy,
and the new one (A/C Delco exact replacement) had more aggressive fins in
the cage. (Of course, the motor burnt out this summer, so I kept the cage
and used a Siemens motor, and I posted the P/N earlier. Siemens motor is
part number PM102/SL1587.
3). Put new foam cell 'gaskets' on the interior duct work. For the dash and
defroster, these plastic pieces were leaking most of the output away under
the dash. I suppose you could also use duct tape, but I just shoved the foam
tape in the joints. A lot of the air was getting away at these seams.
Beyond that, I'm not sure what else to tell you. I'd make sure the air box
is able to get air, that someone on the line didn't leave a piece of tape
over the air inlet or something. Maybe I got a more aggressive squirrel cage
that the original, and it's just moving more air. If so, it was just dumb
luck.
When driving, we usually use the medium fan setting with out any problems
unless it's hot, then only high because of the heat gain from all that
glass. We seldom are in MAX setting.
I've thought about trying to change the programming in the controller to
turn the heater core coolant flow off unless the top lever is in max - A/C -
or bi-level (which doesn't exist). It would make the A/C work better if
there wasn't a hot heater core going at the same time you want to run the
A/C. The only time the coolant valve goes active on ours (turning off the
coolant flow) is when the top lever is in max.
It should do the same thing when the bottom lever is all the way on cold,
most GM cars of the same vintage did. The GMC doesn't, at least not on ours.
Good luck.
Mark Grady
'77 Kingsley
N Webster, IN
mgrady
>
> I have a question for you. You say the air should "shoot out of the dash"
> I would describe mine as crawling out. I first tried this with
> the engine off.
> Well, then I read the engine had to be on so I did that------nothing. Then
> a friend pointed out the high speed relay-------hey changed out
> that puppy.
> That helped got the high speed------but not much more air. Read about
> bad gaskets inside heater box broke it open yeah it was sad. Not to
> mention the darn hornet nest in it. Most of the box was full of a wasp
> nest. Hey I have found the problem-----not! Yes, I have vacuum control
> Got good gaskets and so little air. Any Ideas?
I can only speak from my first hand knowledge of out '77, and I'm not sure
when GM changed the design from 'early' to 'late'. I also had low air flow
when we bought our coach. I did all the things you've done, and these things
too:
1). Replaced all the vacuum hoses that lead to, on and from the dash
programmer (control). They were shot, leaked vacuum and wouldn't operate the
damper doors. There are two primary functions of the air doors, one set that
moves the air flow from heater to the dash to the defroster, and another
that puts the system in recirculate mode for maximum A/C. On our coach, the
recirculate door control mount was bent, so it wouldn't go into MAX mode.
On the GMC, the temp adjust door is operated by a Bowden cable, not vacuum.
I've thought about converting it, but... I just fiddle the setting as
needed. A GM/Harrison Comfortron from that vintage isn't a real pretty
thing.
2). Replaced the high speed +12 supply wiring, which had melted, with a 10ga
wire to carry the current.
3). Put on a new squirrel cage fan. The original one vibrated like crazy,
and the new one (A/C Delco exact replacement) had more aggressive fins in
the cage. (Of course, the motor burnt out this summer, so I kept the cage
and used a Siemens motor, and I posted the P/N earlier. Siemens motor is
part number PM102/SL1587.
3). Put new foam cell 'gaskets' on the interior duct work. For the dash and
defroster, these plastic pieces were leaking most of the output away under
the dash. I suppose you could also use duct tape, but I just shoved the foam
tape in the joints. A lot of the air was getting away at these seams.
Beyond that, I'm not sure what else to tell you. I'd make sure the air box
is able to get air, that someone on the line didn't leave a piece of tape
over the air inlet or something. Maybe I got a more aggressive squirrel cage
that the original, and it's just moving more air. If so, it was just dumb
luck.
When driving, we usually use the medium fan setting with out any problems
unless it's hot, then only high because of the heat gain from all that
glass. We seldom are in MAX setting.
I've thought about trying to change the programming in the controller to
turn the heater core coolant flow off unless the top lever is in max - A/C -
or bi-level (which doesn't exist). It would make the A/C work better if
there wasn't a hot heater core going at the same time you want to run the
A/C. The only time the coolant valve goes active on ours (turning off the
coolant flow) is when the top lever is in max.
It should do the same thing when the bottom lever is all the way on cold,
most GM cars of the same vintage did. The GMC doesn't, at least not on ours.
Good luck.
Mark Grady
'77 Kingsley
N Webster, IN
mgrady
