Paper towel defroster! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

krue · 04-09-2003, 02:06 PM

My heater blower motor is not working, but when I run a jumper from the battery to it, it works fine. How do I test the switch? Is there anything else I need to check? I can't afford to buy a roll of paper towels to defrost my windows every time it rains!

**Palf70Step** · 04-09-2003, 02:58 PM

Mine had a MS farmer replacement switch in it, but I would assume that if your fan isn't working on any setting then the switch is bad. If one setting works, then it might be the springy looking resisteor thing that is bad (sorrry can't remember the real name for it). Only way I know to test the switch is to measure the output to the motor. You can also reach up under the dash and disconnect the plug from the switch and short it from the hot to one of the output connections.

I'm at work so I forget the color code on what is what at the heater switch. From what I have heard, the heater switch is a common failure thing in these trucks. I personnally have never run across one that had a working original switch in them...Either lever broke (like mine) or the switch died.

Hope that helps. BTW I'm replacing all mine too. Hopefully if this stupid rain stops, I'll get the change done this weekend.

bpmcgee · 04-09-2003, 03:22 PM

Here's what I found last weekend on my non-A/C 71:

The brown wire to the switch is hot. If the switch is in one of the on positions, you should get continuity between that pole and at least one of the other poles.

The other poles lead to the resistor block, which you can get to by removing your glove box and unscrewing it from the plenum. That resistor is pretty easy to examine visually for defects. You should also be able to check it for continuity.

Don't forget to check the fuse panel (my problem). There should be a 25A fuse in the "A/C" socket that gives it power.

Brian

krue · 04-09-2003, 08:17 PM

I checked the switch, the brown wire is hot, and some positions show continuity. Tried to jump across switch, got a thump from under the dash somewhere, but no blower motor.

I didn't get to check resistor because it started raining again and I can't afford a shop.

400ex · 04-09-2003, 10:44 PM

Do what bpmcgee said to do - check your fuse.

I had the same problem. No blower when using switch but would work if ran a hot to it. Spent 4 hrs. checking switch, hi speed relay and blower motor resistor. Turns out the fuse was bad. It looked ok, nothing burnt out, but when checking continuity, it was bad..

Save yourself some time...

James

04-09-2003, 02:06 PM	#1
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,450	Paper towel defroster! My heater blower motor is not working, but when I run a jumper from the battery to it, it works fine. How do I test the switch? Is there anything else I need to check? I can't afford to buy a roll of paper towels to defrost my windows every time it rains! __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

04-09-2003, 02:58 PM	#2
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,744	Mine had a MS farmer replacement switch in it, but I would assume that if your fan isn't working on any setting then the switch is bad. If one setting works, then it might be the springy looking resisteor thing that is bad (sorrry can't remember the real name for it). Only way I know to test the switch is to measure the output to the motor. You can also reach up under the dash and disconnect the plug from the switch and short it from the hot to one of the output connections. I'm at work so I forget the color code on what is what at the heater switch. From what I have heard, the heater switch is a common failure thing in these trucks. I personnally have never run across one that had a working original switch in them...Either lever broke (like mine) or the switch died. Hope that helps. BTW I'm replacing all mine too. Hopefully if this stupid rain stops, I'll get the change done this weekend. __________________ 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!

04-09-2003, 08:17 PM	#4
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,450	I checked the switch, the brown wire is hot, and some positions show continuity. Tried to jump across switch, got a thump from under the dash somewhere, but no blower motor. I didn't get to check resistor because it started raining again and I can't afford a shop. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

04-09-2003, 03:22 PM	#3
bpmcgee Registered User Join Date: Mar 2003 Location: Northern Illinois Posts: 2,181	Here's what I found last weekend on my non-A/C 71: The brown wire to the switch is hot. If the switch is in one of the on positions, you should get continuity between that pole and at least one of the other poles. The other poles lead to the resistor block, which you can get to by removing your glove box and unscrewing it from the plenum. That resistor is pretty easy to examine visually for defects. You should also be able to check it for continuity. Don't forget to check the fuse panel (my problem). There should be a 25A fuse in the "A/C" socket that gives it power. Brian

04-09-2003, 10:44 PM	#5
400ex Registered User Join Date: Jan 2003 Location: Damon, Tx Posts: 56	Do what bpmcgee said to do - check your fuse. I had the same problem. No blower when using switch but would work if ran a hot to it. Spent 4 hrs. checking switch, hi speed relay and blower motor resistor. Turns out the fuse was bad. It looked ok, nothing burnt out, but when checking continuity, it was bad.. Save yourself some time... James



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