To have heat, would be nice.......

[thedudeabides86]

Good evening, gearheads!

I’ve got a ‘72 C20 with no heat. It does not have factory air. I’ve had this truck for 25 years and never has the heat worked. Where would you start to figure out the problem? I just replaced the slide switch assembly and when I had it started a couple days ago I played with the switches and had no fan or air pushed out so the blower motor might be bad? Or maybe fuses? I’m still learning the way to fix things on this that I’ve never had to fix before. Any suggestions would be appreciated. Thanks everybody!!

[Astro-Balls]

Does the heater core leak? are the hoses even hooked up to it? or is it bypassed?
Start with the heater core, make sure its in good shape.

[68 P.O.S.]

Do you recall anything from the PO about the heat when you bought it? My limited experience with these trucks is the heater core is usually bad. As you said, it could be a fuse, bad blower motor. Deteriorated vent lines. How's the electrical looking down there?

[Getter-Done]

Pictures would help.

I think the first thing I would do is Pull the fan motor and bench test it.

When you pull the fan out look for Critter Nest also







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[gmc684x4]

Are the heater hoses swapped ?
I had a service van years ago went to the shop many times still no heat i got stuck with it on a long cold road trip reveresed the heater lines better flowing heat

That said blower motor needs to work heater door needs to be open vent tubes needs to be in place
How much leaves and trash has built up in the cowl area ?

[pjmoreland]

There should be a ground wire attached to the blower motor housing on one end and to one of the heater box screws on the other end. Assuming the ground wire is good, you could unplug the power wire from the blower motor and connect a test wire directly from the battery + terminal to the blower motor power terminal to see if the motor will spin. Don't leave this wire connected if you don't hear the motor start to spin, as there could be a short inside the motor, and this test wire is unfused.

The blower fan could be totally clogged with leaves.

[BigBird05]

Start with the basics. If the heater hoses are connected, do they both get hot? If not you have a coolant flow problem.

[BRL]

Originally Posted by thedudeabides86

Good evening, gearheads!

I’ve got a ‘72 C20 with no heat. It does not have factory air. I’ve had this truck for 25 years and never has the heat worked...

You sound like me, (that's a complement) and some of the little projects I've put off on my truck forever.

But even if the fan itself isn't running, shouldn't some heat still be coming through the vents at cruising speed if the switch is slid to the hot position and everything else but the fan is working properly?

[LockDoc]

Originally Posted by BRL

You sound like me, (that's a complement) and some of the little projects I've put off on my truck forever.

But even if the fan itself isn't running, shouldn't some heat still be coming through the vents at cruising speed if the switch is slid to the hot position and everything else but the fan is working properly?

Not if you have something like this in the heater box.... It's a common occurrence.

LockDoc

[franken]

Jump across the fan switch contacts before tearing things apart...

[BRL]

Originally Posted by LockDoc

Not if you have something like this in the heater box.... It's a common occurrence.

LockDoc

Yea, once I opened up a kick panel vent while going 50 and my cab became an instant movie theater pop corn machine with little cotton ball sized fluffy stuff flying everywhere!

Dang vermin!

[thedudeabides86]

Originally Posted by LockDoc

Not if you have something like this in the heater box.... It's a common occurrence.

LockDoc

I'm guessing the silver piece in the picture is the heater core? I've never torn into this myself so I'm in unchartered territory. I'll post the pics of where I'm at in the thread.

[thedudeabides86]

I remember back in high school 23 yrs ago, a coworker wired up a variable speed switch to blow heat but that's been removed. I noticed an orange wire with a boot on the firewall that wasn't plugged in. I tried that. but it didn't make anything work. Here's pics of where I'm at. You'll see the orange wire that's not plugged in just off the center of the photo.

[LockDoc]

Originally Posted by thedudeabides86

I'm guessing the silver piece in the picture is the heater core? I've never torn into this myself so I'm in unchartered territory. I'll post the pics of where I'm at in the thread.

Yes, but that is an A/C truck, heater only is easier. The orange wire is the power for the heater. Turn the heater control for the fan all the way on and see if there is 12 volts to that wire.

LockDoc

[LockDoc]

-
Looking at your under dash picture again it looks like your connector for the blower circuit is not plugged in to the switch on the right side of the heater control panel. In the first picture below you can see where the connector is supposed to be plugged in. the other end of that harness plugs into the blower motor resistor located on the top side of the heater box.

LockDoc

[thedudeabides86]

Originally Posted by LockDoc

-
Looking at your under dash picture again it looks like your connector for the blower circuit is not plugged in to the switch on the right side of the heater control panel. In the first picture below you can see where the connector is supposed to be plugged in. the other end of that harness plugs into the blower motor resistor located on the top side of the heater box.

LockDoc

I unplugged those to see where to start tearing things apart. They were plugged in before I started. Sorry, I shoulda mentioned that.

[LockDoc]

Originally Posted by thedudeabides86

I unplugged those to see where to start tearing things apart. They were plugged in before I started. Sorry, I shoulda mentioned that.

OK, no problem there then.

LockDoc

[thedudeabides86]

So, update on the heat issue. It may not be that I don't have heat, it's that my blower motor doesn't power when the truck is running. We used a jumper from the positive post on the battery to the blower motor and it kicked on. So, where do I go from here? Is the connection at the ignition bad? Bad wire to the fuse panel? Uffdah.

[pjmoreland]

Power for the heater motor comes from the ignition switch, then through the fuse panel on a brown wire on that connector that was unplugged in one of your photos (plugs into heater control switch). Do you have 12V on the brown wire when your ignition is in the run position? Maybe a bad fuse?

[toolboxchev]

The Heater issues on these trucks can be quite extensive. GM never wired the trucks properly.

The Fan itself, on high, can pull too much amperage and cause the under dash harness to burn up ignition switches, wiring, heater switches, and multiple other items.

MAX draw for that wiring and related components for the heater only trucks is either 10 or 15 amps.

[toolboxchev]

A Never Popped kit from Classic Industries is a great upgrade for the levers in heater controls.

Easy Peasy to install. I did have to get some very small nuts and bolts from Ace Hardware due to some sheet metal screws stripping out.

[thedudeabides86]

Originally Posted by toolboxchev

A Never Popped kit from Classic Industries is a great upgrade for the levers in heater controls.

Easy Peasy to install. I did have to get some very small nuts and bolts from Ace Hardware due to some sheet metal screws stripping out.

I searched Classic Industries for Never Popped Kit and didn't find anything. Can you post a link?

[thedudeabides86]

Sooooo, update on the reason I never had any heat in this truck for 25 years.

Are you all sitting down? Good.

The fuse panel has a fuse spot marked "AC" which is 25 amps. Anyone know where this is headed? I put a fut in this slot and the blower motor fired right up and I had heat! This truck does not have AC so I figured I never needed a fuse is this spot. Who'd have thought, it was a simple fix like a fuse. So, that was easy!!

Sabin

[Getter-Done]

Good Deal

Glad you found the problem.






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[HO455]

Excellent! Now the dude will be warm as he abides.