AC/fan switch

[r8rs4lf]

So when I purchased my '72 C10 the previous owner told me to buy a switch because the switch would not operate when pushed all the way (high???) down.

From the top position (I'm assuming is off), one click down is low (works), second click is medium? That works, but when I push the switch all the way down where it says high I get nothing.

I purchased the switch today, got it changed out and got the same results.

Can anyone help?

[Richard]

Originally Posted by r8rs4lf

So when I purchased my '72 C10 the previous owner told me to buy a switch because the switch would not operate when pushed all the way (high???) down.

From the top position (I'm assuming is off), one click down is low (works), second click is medium? That works, but when I push the switch all the way down where it says high I get nothing.

I purchased the switch today, got it changed out and got the same results.

Can anyone help?

A/C relay located all the way on the right of interior ducting. https://classicparts.com/1964-72-a-c-blower-motor-relay Check the cigarette lighter fuse first as that is where the high speed fan gets power from.

[r8rs4lf]

Originally Posted by Richard

A/C relay located all the way on the right of interior ducting. https://classicparts.com/1964-72-a-c-blower-motor-relay Check the cigarette lighter fuse first as that is where the high speed fan gets power from.

Funny you say that as I noticed yesterday that the lighter does not work as well.

I will check tomorrow.

If the fuse is good, the relay is located in the box next to the transmission hump correct?

Also, only because I have not taken a look at the fuse block, does it say cigarette lighter on the fuse box?

[r8rs4lf]

I did find this pic of the fuse block, not sure if it's the same for my year.

https://67-72chevytrucks.com/vboard/...6&postcount=20

I do see a spot that says "cig." It doesn't look like a glass tube fuse goes there.

[Orange Crate]

Relay here arrow A and view A. It is difficult to get to the attaching screws. A 1/4 drive ratchet with a short extension works. If you have another relay, plug that one in and try your switch BEFORE removing the old one.

[r8rs4lf]

Ok so I took a look at the fuse box and there is nothing attached to the "cig" spot. That would explain why the cigarette lighter and "high" on the fan switch are not working correct?

What color wire should be attached there and would it be coming from the relay near the glovebox?

[Casper42]

this is apparently a VERY common issue. My current '72 has an intermittent "no work" but it always goes when I back it off one level from high to medium then back to high. Also, way back in the last 80's my '72 GMC did the exact same thing, but was more prominent than my current truck.

[Richard]

Confused this post with another. Originally I assumed you have A/C. Do you? If not the relay will not be present. See this post as well concerning fan speed issues https://67-72chevytrucks.com/vboard/...d.php?t=862317

[r8rs4lf]

Originally Posted by Richard

Confused this post with another. Originally I assumed you have A/C. Do you? If not the relay will not be present. See this post as well concerning fan speed issues https://67-72chevytrucks.com/vboard/...d.php?t=862317

I do, it's a factory AC truck.

I plan on looking for the relay and following the wire to see if it meets up with the wire from the lighter. Hopefully this will lead me to the promise land. I would assume at this point I don't need to worry about replacing the relay or resistor since there is nothing attached at the fuse box, correct?

[dmjlambert]

The relay is on the right side of the heater core box behind the glove box, very inconvenient to get to unless your glove box and/or heater core box happens to be out.

There is no CIG fuse, the CIG position on the fuse box is unfused always-on power. Normally a 12 gauge red wire connects there and that red wire goes to the cig lighter. The 12 gauge red wire has a piggy back connector on it that looks like this:


There should be a 12 guage orange wire that will plug into the piggy back connector on the red wire. That goes to the high speed relay. Here is the wiring diagram for the A/C system showing the orange wire going to the relay.
https://67-72chevytrucks.com/vboard/...d.php?t=844482

I can’t tell very well from your picture but I think the orange wire plugged into IGN UNFUSED with the piggy back connector on it is probably something smaller than 12 gauge and may be powering something else. I’m not sure about the 12 gauge red wire you have plugged into the ING UNFUSED because I don’t see a 12 gauge piggy back connector on it. So I’m thinking it probably isn’t the one for the cig lighter.

I think it is likely the wire I point to with arrow 1 is the high speed relay 12 gauge wire, and arrow 2 the cig 12 gauge red wire piggy back, but can’t tell where they are plugged in or if they are plugged in, so I’m afraid it is just a guess. If that is not plugged in, it probably needs to be plugged into CIG position.

[r8rs4lf]

Originally Posted by dmjlambert

The relay is on the right side of the heater core box behind the glove box, very inconvenient to get to unless your glove box and/or heater core box happens to be out.

There is no CIG fuse, the CIG position on the fuse box is unfused always-on power. Normally a 12 gauge red wire connects there and that red wire goes to the cig lighter. The 12 gauge red wire has a piggy back connector on it that looks like this:


There should be a 12 guage orange wire that will plug into the piggy back connector on the red wire. That goes to the high speed relay. Here is the wiring diagram for the A/C system showing the orange wire going to the relay.
https://67-72chevytrucks.com/vboard/...d.php?t=844482

I can’t tell very well from your picture but I think the orange wire plugged into IGN UNFUSED with the piggy back connector on it is probably something smaller than 12 gauge and may be powering something else. I’m not sure about the 12 gauge red wire you have plugged into the ING UNFUSED because I don’t see a 12 gauge piggy back connector on it. So I’m thinking it probably isn’t the one for the cig lighter.

I think it is likely the wire I point to with arrow 1 is the high speed relay 12 gauge wire, and arrow 2 the cig 12 gauge red wire piggy back, but can’t tell where they are plugged in or if they are plugged in, so I’m afraid it is just a guess. If that is not plugged in, it probably needs to be plugged into CIG position.
Attachment 2440415

That's a wealth of information. I'll be checking it out and get back......

[r8rs4lf]

Originally Posted by dmjlambert

The relay is on the right side of the heater core box behind the glove box, very inconvenient to get to unless your glove box and/or heater core box happens to be out.

There is no CIG fuse, the CIG position on the fuse box is unfused always-on power. Normally a 12 gauge red wire connects there and that red wire goes to the cig lighter. The 12 gauge red wire has a piggy back connector on it that looks like this:


There should be a 12 guage orange wire that will plug into the piggy back connector on the red wire. That goes to the high speed relay. Here is the wiring diagram for the A/C system showing the orange wire going to the relay.
https://67-72chevytrucks.com/vboard/...d.php?t=844482

I can’t tell very well from your picture but I think the orange wire plugged into IGN UNFUSED with the piggy back connector on it is probably something smaller than 12 gauge and may be powering something else. I’m not sure about the 12 gauge red wire you have plugged into the ING UNFUSED because I don’t see a 12 gauge piggy back connector on it. So I’m thinking it probably isn’t the one for the cig lighter.

I think it is likely the wire I point to with arrow 1 is the high speed relay 12 gauge wire, and arrow 2 the cig 12 gauge red wire piggy back, but can’t tell where they are plugged in or if they are plugged in, so I’m afraid it is just a guess. If that is not plugged in, it probably needs to be plugged into CIG position.
Attachment 2440415

Ok so arrow one is in the first pic. It's plugged in, but it also has another red wire with that plug. It's plugged in to a slot that says GL Box above it. That plug looks like the one you posted with the two red wires on the plug. The only difference is that it has a yellow wire as well. That yellow wire has a connector on the end and was just taped off.

In picture two, you can see that there is a piggy back on that red (arrow #2) wire that has an orange AND a yellow wire. The yellow wire is not connected to anything, but the orange wire goes up in to a loom that heads towards the passenger side.

Picture three is everything I said in one pic.

[Rust_never_sleeps]

Originally Posted by Casper42

this is apparently a VERY common issue. My current '72 has an intermittent "no work" but it always goes when I back it off one level from high to medium then back to high. Also, way back in the last 80's my '72 GMC did the exact same thing, but was more prominent than my current truck.

The wiring path for High is different than for Medium and Low, because it bypasses the resistor(mentioned in above posts as well)
It'll make you crazy until you can wrap your head around that.....or so I have heard ;-)

[r8rs4lf]

So while taking a peek under the dash I found that the cigarette lighter was replaced and the wires were tucked up under the dash as you can see in pic 2. There's only the green wire connected to the rear of the lighter. The red is a single wire that was just wrapped with the green wire. It's not connected to anything, a stand alone wire that looks like it just came with the lighter assembly.

Also in pic two below you can see a red single wire just hanging there. That was also just tucked up underneath. I tried to follow it to see if it goes to the fuse box, but I loose it as it goes up towards the gauges.

[dmjlambert]

OK so the cig lighter wire and its piggy back A/C high speed relay wire is plugged into GL BOX. There is a 15A fuse right below there and that is the fuse for that. It is OK to plug that in there, but fuse may be blown, you can change it to a 25A fuse so it can run the blower on high speed, or you can move that red 12 gauge wire and it's piggy back orange 12 gauge wire from the GL BOX position to the CIG position. The green wire you see is just for the light in the cig lighter. The bare stud sticking out the back of the cig lighter needs the 12 G red wire attached to it. That should get the cig lighter working.
Here is a pic and thread link to discussion of the fuse box so you know what powers what on the fuse box.


Once you get the cig lighter working, you can trace that orange wire connected to the piggy back connector to the high speed relay and see if it is plugged into the high speed relay.

[dmjlambert]

Here is a top down view of the high speed relay from another discussion. Where the arrow is pointing is where a thinner 18 gauge orange wires should be plugged in; that thin wire comes from the blower speed switch. The 12 gauge orange wire you can see in the picture and that comes from the (normally CIG position) fuse panel.

That thread mentions another reason the high speed relay may not be coming on, the thin orange wire was not plugged in to the high speed relay. And finally the AIR COND fuse may be blown, there's another thing to check.

[r8rs4lf]

Originally Posted by dmjlambert

OK so the cig lighter wire and its piggy back A/C high speed relay wire is plugged into GL BOX. There is a 15A fuse right below there and that is the fuse for that. It is OK to plug that in there, but fuse may be blown, you can change it to a 25A fuse so it can run the blower on high speed, or you can move that red 12 gauge wire and it's piggy back orange 12 gauge wire from the GL BOX position to the CIG position. GOT IT! The green wire you see is just for the light in the cig lighter. The bare stud sticking out the back of the cig lighter needs the 12 G red wire attached to it. That should get the cig lighter working.Are you talking about the single red wire hanging from underneath the dash or the red wire that was wrapped with the green wire?
Here is a pic and thread link to discussion of the fuse box so you know what powers what on the fuse box.


Once you get the cig lighter working, you can trace that orange wire connected to the piggy back connector to the high speed relay and see if it is plugged into the high speed relay.

I apologize if I'm confusing you, but I'm trying to make sure I understand exactly what you are saying.

[r8rs4lf]

Originally Posted by dmjlambert

Here is a top down view of the high speed relay from another discussion. Where the arrow is pointing is where a thinner 18 gauge orange wires should be plugged in; that thin wire comes from the blower speed switch. The 12 gauge orange wire you can see in the picture and that comes from the (normally CIG position) fuse panel.

That thread mentions another reason the high speed relay may not be coming on, the thin orange wire was not plugged in to the high speed relay. And finally the AIR COND fuse may be blown, there's another thing to check.

I did actually put my eyes on the relay and saw the 12 gauge orange wire. I will check for the smaller 18 gauge wire as well.

[dmjlambert]

Originally Posted by r8rs4lf

The red is a single wire that was just wrapped with the green wire. It's not connected to anything...

Originally Posted by r8rs4lf

I apologize if I'm confusing you, but I'm trying to make sure I understand exactly what you are saying. ... That should get the cig lighter working.Are you talking about the single red wire hanging from underneath the dash or the red wire that was wrapped with the green wire?

No, not confusing, I'm doing OK if you are. It is quite OK to ask more questions.

So you have some choices here. The aftermarket lighted cig lighter in your truck was not completely hooked up yet, and there is a red wire for it that has not been used yet. There is probably the factory red wire that is not plugged onto the post of the cig lighter that is probably stuffed up there somewhere behind the dash. You can use that one, or you can use the new red wire. I can't tell if the new red wire has a piggy back connector on it. If it does not, and the 12 gauge orange wire for the high speed relay also does not have a piggy back connector on it, you can plug those things into 2 separate positions on the fuse panel. The choices of places to plug stuff in are shown in the fuse panel picture, CIG is unfused always hot, IGN UNFUSED is hot in the key on position and is also unfused, and GL BOX is always on and fused usually with a 15 A fuse but if you plug something in it that draws a lot of power you may need to use a 20 A or 25 A fuse in the GL BOX position.

[r8rs4lf]

Originally Posted by dmjlambert

No, not confusing, I'm doing OK if you are. It is quite OK to ask more questions.

So you have some choices here. The aftermarket lighted cig lighter in your truck was not completely hooked up yet, and there is a red wire for it that has not been used yet. There is probably the factory red wire that is not plugged onto the post of the cig lighter that is probably stuffed up there somewhere behind the dash. You can use that one, or you can use the new red wire. I can't tell if the new red wire has a piggy back connector on it. If it does not, and the 12 gauge orange wire for the high speed relay also does not have a piggy back connector on it, you can plug those things into 2 separate positions on the fuse panel. The choices of places to plug stuff in are shown in the fuse panel picture, CIG is unfused always hot, IGN UNFUSED is hot in the key on position and is also unfused, and GL BOX is always on and fused usually with a 15 A fuse but if you plug something in it that draws a lot of power you may need to use a 20 A or 25 A fuse in the GL BOX position.

I believe that single red wire hanging just to the left of the green wire is probably the original red wire that was hooked up to the original cigarette lighter. It was just tucked up under the dash just like the new cigarette lighter wires were.

So assuming the orange 12 gauge wire is attached to the relay and the smaller 18 gauge wire is there as well, besides moving the plug with the two red wires from the glove box to cig, all I need to do is attach that red wire hanging to the lighter and that should get me HIGH on the fan switch correct?

It's kind of funny understanding how all this works and just because someone didn't hook up the new cigarette lighter created this problem.

My dad always taught me that if you are going to do something do it right the first time. Obviously this was not the case with whoever just mounted the lighter and not understand the consequence that came with it.

I really appreciate your help and I will get under there and get it sorted out.

Another quick question only because I haven't really looked upon there, I only put my phone up there, the stud on the back of the lighter, how does the wire hook up to that?

[dmjlambert]

Originally Posted by r8rs4lf

I believe that single red wire hanging just to the left of the green wire is probably the original red wire that was hooked up to the original cigarette lighter. It was just tucked up under the dash just like the new cigarette lighter wires were.

So assuming the orange 12 gauge wire is attached to the relay and the smaller 18 gauge wire is there as well, besides moving the plug with the two red wires from the glove box to cig, all I need to do is attach that red wire hanging to the lighter and that should get me HIGH on the fan switch correct?

It's kind of funny understanding how all this works and just because someone didn't hook up the new cigarette lighter created this problem.

The cig lighter and high speed fan are not really related and getting one going will not fix the other (probably). But they are often plugged into the same spot on the fuse panel, and getting the cig lighter going will prove you have some power available on the fuse panel position you are trying, and that will get you 1/2 the way there.

[dmjlambert]

Originally Posted by r8rs4lf

I really appreciate your help and I will get under there and get it sorted out.

Another quick question only because I haven't really looked upon there, I only put my phone up there, the stud on the back of the lighter, how does the wire hook up to that?

No problem. The wire hooks up to that stud by a push-on connector. That connector is not very much like any other connector on the truck, it is a female round connector. I'm afraid I don't remember what it looks like.

[r8rs4lf]

Originally Posted by dmjlambert

The cig lighter and high speed fan are not really related and getting one going will not fix the other (probably). But they are often plugged into the same spot on the fuse panel, and getting the cig lighter going will prove you have some power available on the fuse panel position you are trying, and that will get you 1/2 the way there.

Understood!

So it sounds like you are saying that the position where those two red wires are plugged (glove box) in to is not hot meaning the relay is not getting power therefore no HIGH setting?

[r8rs4lf]

I just went outside and moved the plug to the CIG position and I got HIGH to work. That's crazy, it just needed power besides (probably a blown fuse in the glove box position) the fact it was plugged in to the wrong place.

I also looked at the plug on the hanging red wire. I slid it onto the stud on the rear of the lighter, but it would not stay. The new red wire has that exact same plug on one end and the other end has the plug to attach to what looks like a male tab on the fuse box.

It's all starting to come together!!

What about the green wire, could I potentially plug that in to the yellow wire attached to the piggy back in my previous pics?

One more thing, I saw a plug just hanging there and this box attached to the firewall that looks like it belongs there. What is that and does that plug belong on it?

[dmjlambert]

Originally Posted by r8rs4lf

Understood!

So it sounds like you are saying that the position where those two red wires are plugged (glove box) in to is not hot meaning the relay is not getting power therefore no HIGH setting?

Well, that is a possibility, just one of several reasons why the relay is not working. It is possible the relay is bad as well. If you can get the cig lighter working and the wire you use to do that has a piggy back connector where it plugs into the fuse box, you can plug the 12 gauge orange wire that goes to the high speed relay into it and you can be reasonably sure at least the fuse panel side of that orange wire has power. Then go check for voltage on that wire at the relay. If you have a test light like this, you can connect the alligator clip to a good clean ground and probe the connectors and fuse panel points to determine what is getting power.