diagnosing A/C, heat, blower, fan matters, etc... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

sactoC10 · 10-07-2003, 02:36 PM

Help please.

I bought my 71 LWB knowing that the factory A/c was not in working condition, not a big deal. Doign work inside the cab last week I attempted to turn on the heater/fan, whatever and realized that nothing was blowing at all.

So, it is time to start investigating this. Of course I'll start with the fuse, check the wiring, etc. Where is the blower "switch" and how can I tell if it is good or bad? What might anyone suggest I do from there?

Thanks!

71GMC_3/4T · 10-07-2003, 02:58 PM

First, make sure the wire is connected to the fan motor. Outside near the hood hinge.

Next, pull your glove box cardboard and that will allow you to look at all the other things. There's a resistor (coiled wires inside the air tunnel), and a relay that you may find to be the culprit.

sactoC10 · 10-07-2003, 03:52 PM

gotcha...

Replaced the heater core in August, saw these items. I'll check the connection, glove box is no problem, it broke into pieces when I was removing it, so just a big hole there now.

Any trick to getting back to that resistor? I remember thinking that it was in a pretty peculiar place. What after that?

and thanks again!

pierce · 10-07-2003, 04:14 PM

There is a module screwed on the pass side near the kick panel or on it. It's a cheap part to replace and was causing mine not to work. You can test the blower motor by conecting it to the battery to see if it's not clogged w leaves/mouse nest. You can tell if the fan resistor is broke by looking for any splits also.

Huck · 10-07-2003, 05:04 PM

A/C fan not working eigh??
Mr. Obvious suggests you first check the fuse in the fuse box!? Then there is a switch on the heater/Ac control with a plug it behind it---with the switch turned on, try wiggling the rear connector to that switch.
Next there is a relay that attaches to the interior heater box just below the glove box. Make sure the relay is grounded. As Pierce suggests, jumper a wire to the heater motor direct to ensure the fan is OK. After you have done all of the above and it's still not working, come back and we will take you thru steps 6-97 (:>)

sactoC10 · 10-07-2003, 09:28 PM

Errrr, excuse me please for the DUMB rookie move....

It was the ground. The ground, in the engine compartment was not tightened down. Got out the driver, tightened it, and all the fan in the world.

THANKS MUCH!!!

10-07-2003, 02:36 PM	#1
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,055	diagnosing A/C, heat, blower, fan matters, etc... Help please. I bought my 71 LWB knowing that the factory A/c was not in working condition, not a big deal. Doign work inside the cab last week I attempted to turn on the heater/fan, whatever and realized that nothing was blowing at all. So, it is time to start investigating this. Of course I'll start with the fuse, check the wiring, etc. Where is the blower "switch" and how can I tell if it is good or bad? What might anyone suggest I do from there? Thanks!

10-07-2003, 02:58 PM	#2
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	First, make sure the wire is connected to the fan motor. Outside near the hood hinge. Next, pull your glove box cardboard and that will allow you to look at all the other things. There's a resistor (coiled wires inside the air tunnel), and a relay that you may find to be the culprit. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

10-07-2003, 04:14 PM	#4
pierce Registered User Join Date: Sep 2000 Location: Cincinnati,OH,USA Posts: 464	There is a module screwed on the pass side near the kick panel or on it. It's a cheap part to replace and was causing mine not to work. You can test the blower motor by conecting it to the battery to see if it's not clogged w leaves/mouse nest. You can tell if the fan resistor is broke by looking for any splits also. __________________ 69 GMC 1 Ton Longhorn 37 Chevy Coupe

10-07-2003, 03:52 PM	#3
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,055	gotcha... Replaced the heater core in August, saw these items. I'll check the connection, glove box is no problem, it broke into pieces when I was removing it, so just a big hole there now. Any trick to getting back to that resistor? I remember thinking that it was in a pretty peculiar place. What after that? and thanks again!

10-07-2003, 05:04 PM	#5
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	A/C fan not working eigh?? Mr. Obvious suggests you first check the fuse in the fuse box!? Then there is a switch on the heater/Ac control with a plug it behind it---with the switch turned on, try wiggling the rear connector to that switch. Next there is a relay that attaches to the interior heater box just below the glove box. Make sure the relay is grounded. As Pierce suggests, jumper a wire to the heater motor direct to ensure the fan is OK. After you have done all of the above and it's still not working, come back and we will take you thru steps 6-97 (:>)

10-07-2003, 09:28 PM	#6
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,055	Errrr, excuse me please for the DUMB rookie move.... It was the ground. The ground, in the engine compartment was not tightened down. Got out the driver, tightened it, and all the fan in the world. THANKS MUCH!!!



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