Heater won't get real hot. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ryhan87 · 02-02-2011, 10:19 PM

I am having problems getting my heater to blow hot air. So far I have changed my thermostat to a 195. I'm getting hot water to my heater core and out. If I run the truck in the heated shop it blows real hot air but as soon as I move outside it starts blowing cold air. I think my problem is I'm drawing in air from outside rather than in the cab. I've heard that there is a blend air door controlled by vaccuum on the a/c model but is it the same on the non a/c models. Also do you know of a website where I could find detailed microfiche diagramns of are trucks?
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**Classic Heartbeat** · 02-02-2011, 10:23 PM

The non A/C trucks all pull their air from the cowling area. (Outside air) I would say you probably have a partialy blocked heater core or maybe some debree blocking part of the core. WES

**Palf70Step** · 02-02-2011, 10:24 PM

MY first though is the heater core. Even if your drawing in outside air, it should heat up the inside pretty good. Mine is a non AC cab and no they don't use the vacuum control, it's all manual cables.

I still think it is your heater core, but it could be the door. You'll be tearing it down to the safe level in either case from what I remember, so I'd have a new core ready to go in.

What Wes said...I type so slow for being a nerd.

57larry · 02-02-2011, 10:44 PM

I would reverse flush the entire cooling/heating system

BLACK AND BLUE 67-72 · 02-02-2011, 10:54 PM

I'd get a new core and do some cleaning on the heater box, sounds like that is most of your problem.

biggestjohn · 02-02-2011, 11:23 PM

Is it possible that his cables are sticking, and not closing the flapper doors all of the way?

ryhan87 · 02-02-2011, 11:29 PM

I think my heater core is probably fine. I changed my thermostat last night and ran it in the shop up to temp and it was blowing some pretty hot air, but as soon as I backed it outside it started blowing cold air in a matter of like twenty sec. The temp change from indoor to outdoor was pretty extreme from +20 inside to -35 Celsius outside. Is it possible to fit something so my heater will only circulate the warm cab air? I like my old truck but I'm getting sick of freezing in it. It's been below 30 degrees celsius here for like two weeks now. Also anything on the microfiche?
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weircc · 02-02-2011, 11:36 PM

just went through this yesterday where are your heater hoses running too

**passthebuck** · 02-02-2011, 11:39 PM

I had a similar problem. Ended up being a partially blocked heater core. Had it recored & if I leave it on high I have to open the window, even in cold-ass prairie winters like this one...

ryhan87 · 02-03-2011, 12:00 AM

My hot-cold heater control is really hard to move, does that cable just go to my water shutoff valve or would it control a door too? My other two control arms move freely though. Does the lower vent on the pass kick panel supply air to the heater via the same passage as the cowl vent? I'm still not sold on the blocked heater core as I get real hot air blowing out when I run it inside. Also today has warmed up alot outside and my heater blows decent hot air well driving today but still nothing like it did inside.
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makman1297 · 02-03-2011, 12:41 AM

I found my truck had the metal section where the fan seals to the cab was rotted out and would blow most of the hot air under the hood. It was terrible in the winter.

ryhan87 · 02-03-2011, 12:59 AM

Is the upper cowl vent where the fan draws in air connected to the lower pull open vent by your feet on the passengers side? If so would it be possible to hook up the a/c model air shut-off valve up in the cowl to stop the draw of outside air in the winter? Also do the non a/c models need the vac canister by the battery for anything?

02-02-2011, 10:19 PM	#1
ryhan87 Registered User Join Date: Sep 2009 Location: Lloydminster Alberta Posts: 32	Heater won't get real hot. I am having problems getting my heater to blow hot air. So far I have changed my thermostat to a 195. I'm getting hot water to my heater core and out. If I run the truck in the heated shop it blows real hot air but as soon as I move outside it starts blowing cold air. I think my problem is I'm drawing in air from outside rather than in the cab. I've heard that there is a blend air door controlled by vaccuum on the a/c model but is it the same on the non a/c models. Also do you know of a website where I could find detailed microfiche diagramns of are trucks? Posted via Mobile Device

02-02-2011, 10:23 PM	#2
Classic Heartbeat Project Junkie! Fishing Poor!! Join Date: Dec 1999 Location: Olympia,Wa. 98512 Posts: 10,766	Re: Heater won't get real hot. The non A/C trucks all pull their air from the cowling area. (Outside air) I would say you probably have a partialy blocked heater core or maybe some debree blocking part of the core. WES __________________ On-line catolog Classic Heartbeat Pickup Parts WEHEPP@comcast.net Call us Toll Free (888) 338-2502 Like Us on Facebook No appointment necessary. 72 BB Chevy Custom Deluxe / Custom Camper 67 I-6 (Soon to be 5.7 LS1) Panel 68 BB Chevy Short Bed 72 6.0 LQ9 Short Bed Chevy 4X4 Olympia's fastest growing truck parts supplier. Olympia's home for Wayward Chevys Last edited by Classic Heartbeat; 02-02-2011 at 10:25 PM.

02-02-2011, 10:24 PM	#3
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,216	Re: Heater won't get real hot. MY first though is the heater core. Even if your drawing in outside air, it should heat up the inside pretty good. Mine is a non AC cab and no they don't use the vacuum control, it's all manual cables. I still think it is your heater core, but it could be the door. You'll be tearing it down to the safe level in either case from what I remember, so I'd have a new core ready to go in. What Wes said...I type so slow for being a nerd. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! Last edited by Palf70Step; 02-02-2011 at 10:25 PM.

02-02-2011, 10:44 PM	#4
57larry Registered User Join Date: Nov 2007 Location: Indianapolis Posts: 1,161	Re: Heater won't get real hot. I would reverse flush the entire cooling/heating system

02-02-2011, 10:54 PM	#5
BLACK AND BLUE 67-72 Firefighter Join Date: Feb 2001 Location: Yellville, Ar, USA Posts: 1,943	Re: Heater won't get real hot. I'd get a new core and do some cleaning on the heater box, sounds like that is most of your problem. __________________ '72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA

02-02-2011, 11:23 PM	#6
biggestjohn Registered User Join Date: Apr 2010 Location: Russiaville Posts: 203	Re: Heater won't get real hot. Is it possible that his cables are sticking, and not closing the flapper doors all of the way?

02-02-2011, 11:29 PM	#7
ryhan87 Registered User Join Date: Sep 2009 Location: Lloydminster Alberta Posts: 32	Re: Heater won't get real hot. I think my heater core is probably fine. I changed my thermostat last night and ran it in the shop up to temp and it was blowing some pretty hot air, but as soon as I backed it outside it started blowing cold air in a matter of like twenty sec. The temp change from indoor to outdoor was pretty extreme from +20 inside to -35 Celsius outside. Is it possible to fit something so my heater will only circulate the warm cab air? I like my old truck but I'm getting sick of freezing in it. It's been below 30 degrees celsius here for like two weeks now. Also anything on the microfiche? Posted via Mobile Device

02-02-2011, 11:36 PM	#8
weircc Registered User Join Date: Dec 2008 Location: richmond, MO Posts: 794	Re: Heater won't get real hot. just went through this yesterday where are your heater hoses running too

02-02-2011, 11:39 PM	#9
passthebuck Sisyphus was my mentor! Join Date: Sep 2002 Location: Carleton Place, Ontario CANADA Posts: 984	Re: Heater won't get real hot. I had a similar problem. Ended up being a partially blocked heater core. Had it recored & if I leave it on high I have to open the window, even in cold-ass prairie winters like this one... __________________ passthebuck #5642 -TWO 1967 GMC 910's. One with L6/3-on-the tree and the other with 355 w/435hp & a 700r4. -a 2013 Honda Civic as my "sensible" car

02-03-2011, 12:00 AM	#10
ryhan87 Registered User Join Date: Sep 2009 Location: Lloydminster Alberta Posts: 32	Re: Heater won't get real hot. My hot-cold heater control is really hard to move, does that cable just go to my water shutoff valve or would it control a door too? My other two control arms move freely though. Does the lower vent on the pass kick panel supply air to the heater via the same passage as the cowl vent? I'm still not sold on the blocked heater core as I get real hot air blowing out when I run it inside. Also today has warmed up alot outside and my heater blows decent hot air well driving today but still nothing like it did inside. Posted via Mobile Device

02-03-2011, 12:41 AM	#11
makman1297 Registered User Join Date: Mar 2010 Location: Beaufort SC Posts: 583	Re: Heater won't get real hot. I found my truck had the metal section where the fan seals to the cab was rotted out and would blow most of the hot air under the hood. It was terrible in the winter.

02-03-2011, 12:59 AM	#12
ryhan87 Registered User Join Date: Sep 2009 Location: Lloydminster Alberta Posts: 32	Re: Heater won't get real hot. Is the upper cowl vent where the fan draws in air connected to the lower pull open vent by your feet on the passengers side? If so would it be possible to hook up the a/c model air shut-off valve up in the cowl to stop the draw of outside air in the winter? Also do the non a/c models need the vac canister by the battery for anything?



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