Couple Heater issue questions need help bad.

[conoco]

Just bought my 1972 gmc. The heater was only working on one speed, couple days after I got home wouldn’t turn on anymore. I ordered a new fan switch put everything back together and it started working again, only when the switch was all the way down. Went to eat dinner, went back out and now it won’t turn on again. All the fuel look good. So here is my remedies I am thinking.

1.While I was taking everything apart the heater ducts were ripping in two, I am going to buy all new yet work and replace it.

2. I am just going to buy a complete control unit with all new arms, the middle are on mine broke so I took it apart and replaced it but the entire unit is just old and I would rather just spend 100 dollars and buy a whole new unit. I will use the fan switch I just got and install it on the new unit if it doesn’t have one, maybe it’s the unit.

3. I will get a new blower motor also, mine is old and they are not expensive so new one it is. I read on another post that the right hood hinge needs to be removed to get the blower motor out, is this my only option? That’s why it would be nice to take out the AC box.

4. All new cables for the control levers, mine are rusted and hard to move even after lubing them.

5. Since the ducts are being replaced I will replace the resistor switch.

6. My truck has factory AC, but the previous owner took out the compressor an condenser and all that stuff, can I just take out the big ass AC box in the picture attached? Do I need to cap any hoses or anything to do this? Anyone have a reference to follow? Thank you.

I live in Alaska and really need to get this heater working. Does anyone have any ideas or suggestions at all? I don’t know why it starting working and now it stopped I was so damn happy even just blowing on o e speed. Sorry for the long post just need one help desperately. Thank you.

I would really like to just take out the ac if it’s possible I just need reference on how. It takes up so much room and I do t need a in Alaska

[dmjlambert]

An A/C truck has the heater core in the heater box inside the cab, and a non-A/C truck has the heater core in a box that looks similar to the one you show under the hood, although I believe it is smaller. So you would need to change boxes in the cab and under the hood to convert it to a heat-only truck in order to get rid of the large A/C evaporator box under the hood. Also, inside the cab in a heat only truck, the A/C outlets on the dash would not be there. If you convert to heat only, I think those outlets will not do anything. If you keep your A/C setup, you will have the ability to blow warm air out of the A/C outlets if you like. But it will take more restoration if the air diverters are not in good condition. I also believe the holes in the firewall are different between A/C trucks and non-A/C trucks. Other folks here may know more detailed information.

If the fan switch is in the all the way down position, that is the high speed. In an A/C truck, the high speed works via a relay that routes power from the CIG terminal on the fuse panel to the motor, instead of running the voltage through the switch and through the resistors that are in the heater box. So if it does not work at other positions of the switch, I would suspect a bad resistor assembly or problems with the wiring that goes to the switch or resistors.

[truckster]

Originally Posted by dmjlambert

So you would need to change boxes in the cab and under the hood to convert it to a heat-only truck in order to get rid of the large A/C evaporator box under the hood.

The openings in the firewall are different. It would require some welding as well. The second post in this thread shows the differences:

http://67-72chevytrucks.com/vboard/s...d.php?t=419390

[vics stuff]

Was that the 4X4 that was for sale here in Anchorage ?
Vic

[conoco]

Originally Posted by vics stuff

Was that the 4X4 that was for sale here in Anchorage ?
Vic

Yes

[Andy4639]

You need to check the whole system out and if your truck is a AC truck keep it as is. The AC switches are bad about burning up. You can take the switch a part and clean it up and it may work. The wiring for a heater only and AC truck are different animals and you need to check it out good.
A shop manual would be a good investment for this.

[Bobbysgmc]

In a emergency you can run a wire from the battery to the blower motor to make it run.It will only run one speed but at least its something.

[LockDoc]

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If the blower only works on high speed you are probably needing a resistor for the heat blower motor circuit. The reason the blower works on high speed but not low or medium is because the resistor is only used on low and medium speeds. The resistor for the heater is located inside the heater box on the inside of the truck. It would be item #1 in the picture below. (from the assembly manual)

Pretty easy to change it. Unplug the connector by prying up on it with a small screw driver working from side to side, and remove the two 1/4" screws. I would recommend using a little dielectric grease on the spade terminals before you plug the connector back in.

LockDoc

[conoco]

Originally Posted by LockDoc

-
If the blower only works on high speed you are probably needing a resistor for the heat blower motor circuit. The reason the blower works on high speed but not low or medium is because the resistor is only used on low and medium speeds. The resistor for the heater is located inside the heater box on the inside of the truck. It would be item #1 in the picture below. (from the assembly manual)

Pretty easy to change it. Unplug the connector by prying up on it with a small screw driver working from side to side, and remove the two 1/4" screws. I would recommend using a little dielectric grease on the spade terminals before you plug the connector back in.

LockDoc

Thank you very much, I'll pick up the resistor tomorrow. You wouldnt by chance have the same diagram for where all the cables connect to w ok old you. 2 of them are hooked up and working , but one of them cam loose when I took the temp control unit out and can figure out where it hooks to under the dash. I must have hung upside down for 2 hours trying to find it. Thanks again for your help.

[LockDoc]

Originally Posted by conoco

Thank you very much, I'll pick up the resistor tomorrow. You wouldnt by chance have the same diagram for where all the cables connect to w ok old you. 2 of them are hooked up and working , but one of them cam loose when I took the temp control unit out and can figure out where it hooks to under the dash. I must have hung upside down for 2 hours trying to find it. Thanks again for your help.

Sorry I don't, but it should attach in the same area as the others. The lever that it is supposed to be attached to may be broken off of the assembly. That is a common occurrence on those because the levers are made of pot metal. You can buy kits to rebuild them..

LockDoc

[mrein3]

Yes and yes. I converted a non-AC truck to factory AC. EVERY switch plug I found used, EVERY SINGLE ONE OF THEM was melted. I'm not sure of the name but what I call the switch plug is the plug behind the control panel that plugs into the back of the fan speed switch. That plug is likely melted on your truck in addition to the resister block not working.
Order a new plastic plug then get part numbers 725145 and 725147 from NAPA. My Chevelles and truck have so many of those wire ends that I stock them in my box full of electrical connectors.

Get the ends from NAPA, get the plastic plug from an online supplier, write down what color goes in which hole in the plug, then re-do all the ends of the wires that connect in to that plug behind the switch.

The reason those plugs all melt is simple. The factory wiring makes the fan spin slower by reducing the voltage to the fan via that resistor block. When you step down the 12 volts between the fan and the switch via that resistor block, that voltage has to go some place. The resistance causes heat, the heat works back through the conductive wire and melts the plastic plug. There is also resistance in the plug connection from 50 years of oxidation in those plug ends. Putting new ends on those wires will reduce the resistance at that connection at the plug and in theory allow your new plastic plug to live a little longer than if it was trying to connect through 50 years of oxidation at the connection. It will melt again eventually but the first on made it 50 years. Let the next guy worry about fixing it the next time.

Originally Posted by Andy4639

You need to check the whole system out and if your truck is a AC truck keep it as is. The AC switches are bad about burning up. You can take the switch a part and clean it up and it may work. The wiring for a heater only and AC truck are different animals and you need to check it out good.
A shop manual would be a good investment for this.

Originally Posted by LockDoc

-
If the blower only works on high speed you are probably needing a resistor for the heat blower motor circuit. The reason the blower works on high speed but not low or medium is because the resistor is only used on low and medium speeds. The resistor for the heater is located inside the heater box on the inside of the truck. It would be item #1 in the picture below. (from the assembly manual)

Pretty easy to change it. Unplug the connector by prying up on it with a small screw driver working from side to side, and remove the two 1/4" screws. I would recommend using a little dielectric grease on the spade terminals before you plug the connector back in.

LockDoc

[cebra]

You may want to pick up a factory service manual (cheap on ebay) so you have it for reference on future repairs. I know I use mine a lot and all the information you are looking for will be in there.