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

68 ReNay · 11-22-2008, 09:21 PM

i've got a 68 C-10, 350, auto, (non-AC)....

the heater blows luke warm at best and the blower would come on and off (loose prongs on heater switch), so...

i replaced the heater core, heater switch and all the gaskets (pulled off interior and exterior boxes). now all the speeds work great, it blows really hard too - but - still won't blow hot. i noticed that the heater blower speed resistor is falling apart (original cardboard type base). would that have anything to do with it. by it's title it doesn't seem like it - but i can't imagine what else the problem could be.

(my old 72 would sweat me out of the cab in winters. this 68 won't even defrost the windows)

any help is greatly appreciated!!!

oldblue1968chevy · 11-22-2008, 09:32 PM

my 68 dont defrost the windows either..but havent torn into it yet..whats the first thing to look for..mine blows a lil bit not very hard..and its barely luke warm also...what do i look for thanks

Brad · 11-22-2008, 09:47 PM

Is your coolant level low? That would be the first thing to check. There was another thread similar just this week. I'll try to find it.
Here ya go: http://67-72chevytrucks.com/vboard/s...ghlight=heater

FLEET72 · 11-22-2008, 09:48 PM

is there a valve in the heater hoses/lines? Is one of the fittings (water pump or manifold) plugged up with rust? With the motor running at temperature, are the heater hoses hot?

The resistor is in the airflow to cool it off while it is changing voltage to heat.

Quote:

Originally Posted by 68 ReNay

i've got a 68 C-10, 350, auto, (non-AC)....

the heater blows luke warm at best and the blower would come on and off (loose prongs on heater switch), so...

i replaced the heater core, heater switch and all the gaskets (pulled off interior and exterior boxes). now all the speeds work great, it blows really hard too - but - still won't blow hot. i noticed that the heater blower speed resistor is falling apart (original cardboard type base). would that have anything to do with it. by it's title it doesn't seem like it - but i can't imagine what else the problem could be.

(my old 72 would sweat me out of the cab in winters. this 68 won't even defrost the windows)

any help is greatly appreciated!!!

Longhorn Man · 11-22-2008, 09:48 PM

the resistor is what selects the blower speeds, so that isn't the issue.
Since you replaced the core, there's only a few options left, either your coolant level is low, or the hoses aren't routed properly (one to the intake, and the other to the water pump or to the rad) Or, the flapper in the heater box isn't making a good seal, either from bed seals, or not moving all the way to close the door from cold outside air.

Wrenchbender Ret · 11-23-2008, 11:16 AM

With the engine warm & running wrap your hand around a heater hose. You should not be able to hold on for more then 2-3 seconds. Both should be same. If one is hot & the other is not ther is poor circulation. I take it you have a good thermostat in it. If they both are hot its like Longhorn says the flaper is not closing.

FRENCHBLUE72 · 11-23-2008, 11:24 AM

I just fixed this problem on my blazer the cable had somehow came off the little diverter box door and I would only get luke warm air. I slipped the cable end loop back on and now I have hot air..

cdowns · 11-23-2008, 11:28 AM

what temp is your thermostat?do you have the hoses routed correctly one from the water pump and one from the radiator?

11-22-2008, 09:21 PM	#1
68 ReNay Registered User Join Date: Sep 2005 Location: KANSAS Posts: 23	Heater won't blow hot i've got a 68 C-10, 350, auto, (non-AC).... the heater blows luke warm at best and the blower would come on and off (loose prongs on heater switch), so... i replaced the heater core, heater switch and all the gaskets (pulled off interior and exterior boxes). now all the speeds work great, it blows really hard too - but - still won't blow hot. i noticed that the heater blower speed resistor is falling apart (original cardboard type base). would that have anything to do with it. by it's title it doesn't seem like it - but i can't imagine what else the problem could be. (my old 72 would sweat me out of the cab in winters. this 68 won't even defrost the windows) any help is greatly appreciated!!!

11-22-2008, 09:32 PM	#2
oldblue1968chevy Grandpa in the rustmobile... Join Date: Nov 2008 Location: Spokane WA/Viola TN Posts: 11,422	Re: Heater won't blow hot my 68 dont defrost the windows either..but havent torn into it yet..whats the first thing to look for..mine blows a lil bit not very hard..and its barely luke warm also...what do i look for thanks __________________ John Goose-1968 C10 355,9.32-1CR, Vortec Heads ,262 voodoo, 3.73:1 3OTT (HS ride/beater/farm truck) http://67-72chevytrucks.com/vboard/s...d.php?t=317684 Grams 53-1953 Chevrolet Belair http://67-72chevytrucks.com/vboard/s...=1#post4327784 1969 Chevy C10 Shortbed 4.5/6?" Frame off resto http://67-72chevytrucks.com/vboard/s...d.php?t=548136 1999 Toyota Tacoma 4x4

11-22-2008, 09:47 PM	#3
Brad Out of the carpool lane. Join Date: Jan 2000 Location: Clark Co, WA Posts: 5,673	Re: Heater won't blow hot Is your coolant level low? That would be the first thing to check. There was another thread similar just this week. I'll try to find it. Here ya go: http://67-72chevytrucks.com/vboard/s...ghlight=heater __________________ 1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten... Last edited by Brad; 11-22-2008 at 09:54 PM.

11-22-2008, 09:48 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Heater won't blow hot the resistor is what selects the blower speeds, so that isn't the issue. Since you replaced the core, there's only a few options left, either your coolant level is low, or the hoses aren't routed properly (one to the intake, and the other to the water pump or to the rad) Or, the flapper in the heater box isn't making a good seal, either from bed seals, or not moving all the way to close the door from cold outside air.

11-23-2008, 11:16 AM	#6
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,228	Re: Heater won't blow hot With the engine warm & running wrap your hand around a heater hose. You should not be able to hold on for more then 2-3 seconds. Both should be same. If one is hot & the other is not ther is poor circulation. I take it you have a good thermostat in it. If they both are hot its like Longhorn says the flaper is not closing.

11-23-2008, 11:24 AM	#7
FRENCHBLUE72 PROJECT 7DEUCE Join Date: Dec 2002 Location: GRANTS PASS OR Posts: 21,608	Re: Heater won't blow hot I just fixed this problem on my blazer the cable had somehow came off the little diverter box door and I would only get luke warm air. I slipped the cable end loop back on and now I have hot air.. __________________ GO BIG GREEN GO DUCKS MEMBER #6377 72 k-5 daily driver 6'' lift 35'' 350-350-205 slowly getting rust free. Project "7DEUCE" check out my build http://67-72chevytrucks.com/vboard/s...d.php?t=267665 Tim Powell..R.I.P EastSideLowlife..... R.I.P..

11-23-2008, 11:28 AM	#8
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Heater won't blow hot what temp is your thermostat?do you have the hoses routed correctly one from the water pump and one from the radiator? __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

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