Heater blower motor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**johnmiller66** · 01-23-2021, 05:48 PM

Any ideas on a problem I have on my 72 GMC. Its a non air truck. The blower motor for my heater won't come on unless I run a ground from the blower motor housing to a ground bolt on the body. When I attach the wire to the ground there is a small spark. The heater then works like it should, but will drain the battery dead if I leave the ground wire hooked up.
Thanks for any replies.

Andy4639 · 01-23-2021, 08:08 PM

So if you turn the heater off inside the truck with said wire it still running? I would be looking at the switch on the middle arm in the cab. It operates the fan.

**johnmiller66** · 01-23-2021, 10:16 PM

With the ground wire hooked up it all works as it should other than draining the battery. Ive been working on it today and added a couple of more ground straps from the cab to the frame. Still have the same issue of needing the ground wire on the blower motor housing but after adding the other grounds, my housing ground wire doesn't spark anymore. Hopefully the extra grounds will keep me from having a dead battery in the morning.

**LockDoc** · 01-23-2021, 10:33 PM

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Here is a picture of an original '67-'72 blower motor ground wire and connection points. All blower motors need it.

LockDoc

**johnmiller66** · 01-23-2021, 10:45 PM

LockDoc, thank you sir for the picture. Makes sense that it made my blower work when I put the ground wire on. I just assumed that it got its ground from the screws mounting it to the firewall and I wasn't getting a good connection there.

RustyPile · 01-23-2021, 10:48 PM

The problem isn't in the grounding of the blower motor.. That ground wire is required because the blower motor is mounted on a non-metallic housing... Does the blower motor continue to run after the ignition switch is turned off?? If so, the power feed to the switch is connected to an "always hot" source.. It should be connected to a power source that's powered from the ignition switch..

Andy4639 · 01-24-2021, 12:41 PM

OK the fan motor has to have the ground strap as in Doc's picture. This however shouldn't make the fan keep running. This is how it comes from the factory.

As I asked in my first post the fan keeps running even after you cut it off with the middle lever inside the truck? If so it's wired up wrong and you need to find out where the 12 volts is feeding from. It should only get 12 volts when the lever is pushed to the passenger side to turn the fan motor on.

**VetteVet** · 01-25-2021, 09:28 AM

The power for the heater comes from the key switch via a 12 gauge brown wire at the ACC terminal. It runs to the fuse panel to the accessory side. It only does this when the key is on in the run or acc mode.
The other side of the fuse panel is the battery power, constant on side. If there is a short behind the panel it would provide the problem you are having. The heater fuse should be the only path for power to the heater fan switch and the speed resistor. If you pull the fuse, 10 amp, then you should not see the ground leak you have. This will separate the key to fuse circuit and the fuse panel to heater switch to fan circuit.
If the fan runs with the key off then it would be a large draw, but you have a low draw which would be a short between a small load like the heater switch light and the switch. Still the key would have to be on to power the heater switch light.
You should place a multimeter set on amps between the fan ground wire and the ground spot and measure the draw with the key off. Post back with the reading.

**johnmiller66** · 01-25-2021, 06:25 PM

I got a chance to dig into it again this afternoon. I pulled the fuse as you suggested and the ground leak went away. I pulled the fuse block and put it a different one i had on the shelf and that seems to have fixed my problem. I appreciate everyone's help in figuring this out.
JM

01-23-2021, 05:48 PM	#1
johnmiller66 Active Member Join Date: Mar 2014 Location: Wichita Kansas Posts: 100	Heater blower motor Any ideas on a problem I have on my 72 GMC. Its a non air truck. The blower motor for my heater won't come on unless I run a ground from the blower motor housing to a ground bolt on the body. When I attach the wire to the ground there is a small spark. The heater then works like it should, but will drain the battery dead if I leave the ground wire hooked up. Thanks for any replies. Last edited by johnmiller66; 01-23-2021 at 07:21 PM. Reason: just because

01-23-2021, 08:08 PM	#2
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Heater blower motor So if you turn the heater off inside the truck with said wire it still running? I would be looking at the switch on the middle arm in the cab. It operates the fan. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

01-23-2021, 10:16 PM	#3
johnmiller66 Active Member Join Date: Mar 2014 Location: Wichita Kansas Posts: 100	Re: Heater blower motor With the ground wire hooked up it all works as it should other than draining the battery. Ive been working on it today and added a couple of more ground straps from the cab to the frame. Still have the same issue of needing the ground wire on the blower motor housing but after adding the other grounds, my housing ground wire doesn't spark anymore. Hopefully the extra grounds will keep me from having a dead battery in the morning.

01-23-2021, 10:33 PM	#4
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,321	Re: Heater blower motor - Here is a picture of an original '67-'72 blower motor ground wire and connection points. All blower motors need it. LockDoc Attached Images __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

01-23-2021, 10:45 PM	#5
johnmiller66 Active Member Join Date: Mar 2014 Location: Wichita Kansas Posts: 100	Re: Heater blower motor LockDoc, thank you sir for the picture. Makes sense that it made my blower work when I put the ground wire on. I just assumed that it got its ground from the screws mounting it to the firewall and I wasn't getting a good connection there.

01-23-2021, 10:48 PM	#6
RustyPile Registered User Join Date: Dec 2017 Location: Elkhart, Texas Posts: 1,526	Re: Heater blower motor The problem isn't in the grounding of the blower motor.. That ground wire is required because the blower motor is mounted on a non-metallic housing... Does the blower motor continue to run after the ignition switch is turned off?? If so, the power feed to the switch is connected to an "always hot" source.. It should be connected to a power source that's powered from the ignition switch..

01-24-2021, 12:41 PM	#7
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Heater blower motor OK the fan motor has to have the ground strap as in Doc's picture. This however shouldn't make the fan keep running. This is how it comes from the factory. As I asked in my first post the fan keeps running even after you cut it off with the middle lever inside the truck? If so it's wired up wrong and you need to find out where the 12 volts is feeding from. It should only get 12 volts when the lever is pushed to the passenger side to turn the fan motor on. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

01-25-2021, 09:28 AM	#8
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,703	Re: Heater blower motor The power for the heater comes from the key switch via a 12 gauge brown wire at the ACC terminal. It runs to the fuse panel to the accessory side. It only does this when the key is on in the run or acc mode. The other side of the fuse panel is the battery power, constant on side. If there is a short behind the panel it would provide the problem you are having. The heater fuse should be the only path for power to the heater fan switch and the speed resistor. If you pull the fuse, 10 amp, then you should not see the ground leak you have. This will separate the key to fuse circuit and the fuse panel to heater switch to fan circuit. If the fan runs with the key off then it would be a large draw, but you have a low draw which would be a short between a small load like the heater switch light and the switch. Still the key would have to be on to power the heater switch light. You should place a multimeter set on amps between the fan ground wire and the ground spot and measure the draw with the key off. Post back with the reading. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

01-25-2021, 06:25 PM	#9
johnmiller66 Active Member Join Date: Mar 2014 Location: Wichita Kansas Posts: 100	Re: Heater blower motor I got a chance to dig into it again this afternoon. I pulled the fuse as you suggested and the ground leak went away. I pulled the fuse block and put it a different one i had on the shelf and that seems to have fixed my problem. I appreciate everyone's help in figuring this out. JM



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