Home » Public Forums » GMCnet » Fan switch/ heater stuck on broil
| Fan switch/ heater stuck on broil [message #96072] |
Mon, 16 August 2010 13:23  |
Smitty52
Messages: 181
Registered: July 2007
Karma: 0
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The AC works great but I only have one fan speed no matter where the switch is located. I remember on my old J10 Jeep that it had a resister plate or something like that that I had to replace to get the multiple fan speed to work correctly. Does the GMC use the same system? If so where is it and what do I ask for to get a new one?
The PO had put in a manual water valve in the heater hose to shut off coolant to the heater. Seems the heat is on all the time unless the valve is closed. I would like it to work correctly. Again, I assume there is a water control valve for the heater that works off a cable to the dash controls. Are these valves still available? I am going to spend some time lubing pivot points and cables but I think the PO had used the water valve technique for so long that the original heater valve will never recover.
Thoughts from the list? No sense me fussing for hours if someone has devised a simple fix.
Wayne and Lisa,
Bolton Landing, NY,
Patriot Guard Rider,
Standing for those who stood for us.
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| Re: [GMCnet] Fan switch/ heater stuck on broil [message #96078 is a reply to message #96072] |
Mon, 16 August 2010 13:41  |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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Wayne,
Regarding the heater valve, on my 73 coach the OEM valve was vacuum operated -- I believe this remained the same during the production life of the GMC. Here is a photo of the replacement valve and the info for same, purchased at Autozone. http://www.gmcmhphotos.com/photos/showphoto.php?photo=30899&title=gmc-motorhome-009&cat=4620
Manual cut-off valves are also an advantage -- if you should have a leak in the heater core you can isolate it quickly.
Dennis Sexton
73 PD 230
Germantown, TN
USA
-----Original Message-----
From: Wayne E LaMothe <superglider@juno.com>
To: gmclist@temp.gmcnet.org
Sent: Mon, Aug 16, 2010 1:23 pm
Subject: [GMCnet] Fan switch/ heater stuck on broil
The AC works great but I only have one fan speed no matter where the switch is
ocated. I remember on my old J10 Jeep that it had a resister plate or
omething like that that I had to replace to get the multiple fan speed to work
orrectly. Does the GMC use the same system? If so where is it and what do I
sk for to get a new one?
The PO had put in a manual water valve in the heater hose to shut off coolant to
he heater. Seems the heat is on all the time unless the valve is closed. I
ould like it to work correctly. Again, I assume there is a water control valve
or the heater that works off a cable to the dash controls. Are these valves
till available? I am going to spend some time lubing pivot points and cables
ut I think the PO had used the water valve technique for so long that the
riginal heater valve will never recover.
Thoughts from the list? No sense me fussing for hours if someone has devised a
imple fix.
-
ayne and Lisa,
olton Landing, NY,
78 Royale center kitchen,
Patriot Guard Rider,
tanding for those who stood for us.
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MCnet mailing list
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Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: [GMCnet] Fan switch/ heater stuck on broil [message #96122 is a reply to message #96072] |
Mon, 16 August 2010 17:30 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Wayne,
You should start by going to the Tech area of www.gmcws.org and downloading
the pamphlet by Zay Brand, "Separating Hot from Cold". It gives detailed
information on all three GMCMH HVAC variants, including possible
improvements.
The temperature is mainly controlled by mixing hot and cold air, using a
deflector door controlled by a cable which you can see at the left side of
the HVAC box under the driver's "hood". Right below that there is a
connector plug; it connects to the resistor pack which extends into the HVAC
air stream.
Because the temperature control door seals are generally in bad shape, and
the vacuum controlled heater shutoffs less than 100% effective, a lot of us
use a manual valve to turn off the H2O flow during warm weather to improve
cooling.
The HVAC blower operates at high speed only when the engine is running
(alternator producing) because it's connected through a relay, under the
right hood, which selects the alternator at Hi; otherwise the resistor pack
is used, with its supply from the battery side of the isolator (0.7 VDC
lower voltage).
HTH,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Mon, Aug 16, 2010 at 2:23 PM, Wayne E LaMothe <superglider@juno.com>wrote:
>
>
> The AC works great but I only have one fan speed no matter where the switch
> is located. I remember on my old J10 Jeep that it had a resister plate or
> something like that that I had to replace to get the multiple fan speed to
> work correctly. Does the GMC use the same system? If so where is it and
> what do I ask for to get a new one?
> ...
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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: Fan switch/ heater stuck on broil [message #96220 is a reply to message #96072] |
Tue, 17 August 2010 14:01 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I have both the vacuum controlled valve and the manual shut off. The vacuum valve does NOT completely shutoff the water flow. Just take a look inside of one of those vacuum valves and you will see why.
You and buy a ball valve with the appropriate fittings and 2 hose clamps for $10 to $15 at Lowes or Home Depot. I think I found that PEX fittings were a good fit for our heater hoses. One screwdriver, a razor knife, and 10 minutes is all you need to install it.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Fan switch/ heater stuck on broil [message #96221 is a reply to message #96220] |
Tue, 17 August 2010 14:08 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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The heater resistor package is on the driver's side of the heater box. Has four wires running into it. The yellow wire may have been cut off, so that the fan does not run all the time.
Tom Phipps,
75 GMC Ex-Avion
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: Fan switch/ heater stuck on broil [message #96223 is a reply to message #96220] |
Tue, 17 August 2010 14:16 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| Ken Burton wrote on Tue, 17 August 2010 14:01 |
I have both the vacuum controlled valve and the manual shut off. The vacuum valve does NOT completely shutoff the water flow. Just take a look inside of one of those vacuum valves and you will see why.
You and buy a ball valve with the appropriate fittings and 2 hose clamps for $10 to $15 at Lowes or Home Depot. I think I found that PEX fittings were a good fit for our heater hoses. One screwdriver, a razor knife, and 10 minutes is all you need to install it.
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I should have noted that GM uses the cabin heater and the auxiliary hot water heater to circulate hot coolant from the back of the heads / intake manifold. DO NOT SHUT OFF BOTH the house hot water coolant line and the cabin heater with ball valves at the same time. I have no ball valve in my aux heater line so that is never a problem for me.
I believe Oldsmobile / GM used that crappy controlled leak vacuum valve on the Toronado and other vehicles to allow some coolant flow from the back of the engine at all times. On the GMC the "controlled leak valve" was not necessary due to the house water heater loop but why change it an use a different part.
I have read where some people have shut off or eliminated the engine assisted hot water heater for reasons I do not understand. If you have done this then DO NOT install a ball valve in the cabin heater line.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Fan switch/ heater stuck on broil [message #96237 is a reply to message #96223] |
Tue, 17 August 2010 17:03 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Ken,
I don't believe there's any cause for concern about completely blocking the
external return paths (heaters) on the 455/403. If there were, I'd expect
there to be some provision to return flow from both banks, rather than only
the left. Also, the X7525 manual's explanation of the coolant flow is quite
explicit in describing the flow aft around the cylinders, below the lower
limit of piston ring travel, then up into the heads and forward to the
return into the intake manifold and thermostat housing. The external
circulation is not mentioned at all, as if it's of little or no importance.
JMHO,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Tue, Aug 17, 2010 at 3:16 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Ken Burton wrote on Tue, 17 August 2010 14:01
> ...I should have noted that GM uses the cabin heater and the auxiliary hot
> water heater to circulate hot coolant from the back of the heads / intake
> manifold. DO NOT SHUT OFF BOTH the house hot water coolant line and the
> cabin heater with ball valves at the same time. I have no ball valve in my
> aux heater line so that is never a problem for me.
>
> I believe Oldsmobile / GM used that crappy controlled leak vacuum valve on
> the Toronado and other vehicles to allow some coolant flow from the back of
> the engine at all times. On the GMC the "controlled leak valve" was not
> necessary due to the house water heater loop but why change it an use a
> different part.
> ...
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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] Fan switch/ heater stuck on broil [message #96240 is a reply to message #96237] |
Tue, 17 August 2010 17:28 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Ooops! ...rather than only the RIGHT... :-)
Oh yeah, I doubt if any of those industrial Olds installations, such as
agricultural pump prime movers, included external heaters.
Ken H.
On Tue, Aug 17, 2010 at 6:03 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
> Ken,
>
> I don't believe there's any cause for concern about completely blocking the
> external return paths (heaters) on the 455/403. If there were, I'd expect
> there to be some provision to return flow from both banks, rather than only
> the left. Also, the X7525 manual's explanation of the coolant flow is quite
> explicit in describing the flow aft around ...
>
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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] Fan switch/ heater stuck on broil [message #96245 is a reply to message #96237] |
Tue, 17 August 2010 18:16 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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On Aug 17, 2010, at 4:03 PM, Ken Henderson wrote:
> Ken,
>
> I don't believe there's any cause for concern about completely blocking the
> external return paths (heaters) on the 455/403. If there were, I'd expect
> there to be some provision to return flow from both banks, rather than only
> the left. Also, the X7525 manual's explanation of the coolant flow is quite
> explicit in describing the flow aft around the cylinders, below the lower
> limit of piston ring travel, then up into the heads and forward to the
> return into the intake manifold and thermostat housing. The external
> circulation is not mentioned at all, as if it's of little or no importance.
>
> JMHO,
>
> Ken H.
I agree with you on this Ken. In fact, there is a restrictor in the fitting for the hose that goes to the back water heater so as to not make it too hot.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] Fan switch/ heater stuck on broil [message #96278 is a reply to message #96245] |
Wed, 18 August 2010 00:12 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I am of a different opinion and do not intend to block it completely just to find out.
Also I thought that there was an internal crossover in the manifold so there is some flow from both heads through that intake manifold port to the heater. I would have to look at an intake manifold again to make sure. I do not have one readily available to look at for sure.
So to play it safe I would not block both return routes at the same time.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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