1983 c20 blower only works on high

[ZXT]

Alright, here's the deal. I have an 83 c20 (4 door, long bed, 454) and the blower only blows on high. Now, you're thinking it's the resistor - it's not. Replaced it twice, and it have tested the continuity. The fan switch and relay have been replaced as well. All that I can think of now is that there could be a short in a wire somewhere and that's causing no voltage to be received to the blower.

Any thoughts? What wires should I trace out? Any schematics?

Thanks!

[rich weyand]

'83 wiring manual is here:
http://www.73-87chevytrucks.com/tech..._30_and_ST.pdf

Download it, then open it, or it takes forever to render.

[gramps77]

opposite problem.
My 77 only works on the 3 lower settings and NOT on high. It just shuts it all right off
Seriously thinking about going to Vintage Air

[ZXT]

Awesome! Thanks for sharing. That'll help a lot. I'll start tracking down the wires.

Thanks!

[rich weyand]

Originally Posted by gramps77

opposite problem.
My 77 only works on the 3 lower settings and NOT on high. It just shuts it all right off
Seriously thinking about going to Vintage Air

There's an orange wire from the switch, from the resistor, and from the blower that are all connected together in a splice. The only way to lose HI while keeping MED and LO, is for the orange wire to be broken between the switch and the splice, or for the switch to be broken on the contact the orange wire connects to. Everything else is OK or you would not have LO and MED.

Check the orange wire from the switch to the splice for breaks. Make sure the orange wire is connected well (contacts are clean etc) to the switch, and make sure the splice is intact. You can also disconnect the connector from the switch and check resistance between the brown wire connection on the back of the switch and the orange wire connection on the back of the switch to make sure the switch is OK.

[ZXT]

When checking for voltage at the switch I have 11.78 volts at all of the wires ( Grayish with a white line, blue, and kind of a beige color) except for the orange. Is this correct?

Thanks.

[rich weyand]

Nope. Orange wire is broken. All of the wires are connected through the switch and the resistor. You should see voltage on all of them. Track the orange wire to the switch to the splice, and check the splice and the switch.

[ZXT]

Where is this splice located?

I really appreciate your help.

[rich weyand]

Don't know; the circuit diagram doesn't say. You have to follow the orange wire through the wiring harness from behind the switch. It's heading for the blower motor and the resistor. At some point, there is a splice, with the wire splitting up between the switch and the blower motor. My bet is that the orange wire from the switch has corroded and broken off the splice.

[ZXT]

I'll start tracing it. I don't have an orange wire coming from the blower motor, but I do have one running to the relay that has the output wire for the blower. I assume that's it.

Thanks!

[rich weyand]

Let me look at the wiring diagram again. Something fishy here....

[rich weyand]

OK, let me try again. The wiring diagram for 1977 shows it as a black w/orange wire, that goes through the firewall with a grommet, along with a brown and a light blue wire, and connects to a connector that plugs onto the resistor. There is another black and orange wire that is also connected to that same position on the connector, that connects to the blower. No relay shown. Are you sure you aren't mistaking the resistor for a relay? In any case, the black w/orange wire is broken between the switch and the resistor connector, probably at the connector itself. No separate splice, the connection is made on the resistor connector.

[rich weyand]

Here's the piece of the diagram I am talking about.



The three wires come through the firewall from the switch. Note how the black w/orange wire 52A connects to the resistor, and another black w/orange wire 52B goes from the resistor to the motor. The black w/orange wire 52A between the resistor and the switch is broken, probably right there at that connection.

[ZXT]

A 77 must be different because i don't have a black w/ orange wire. I have 4 wires coming from my switch, and it seems like there would be one wire with no voltage for the ground. When I jump from the wire with no voltage to any of the other 3, the fan comes on full blast.

[rich weyand]

That is the diagram for a 77.

There is no ground at the switch. The whole truck is ground. There is no separate wire for ground. There is only BAT (brown) and the three speed wires that go through the firewall to the resistor.

The wire from the HI connection (orange on the 78 diagram, black with orange on the 77 diagram) is the HI speed wire, that goes directly to the blower motor. The switch is supposed to connect the brown wire to the orange wire to get HI. When you jumper that connection, the blower goes on HI, so the switch is probably broken or that contact internally is burned.

[ZXT]

How is is ground by the truck if it is a plastic switch mounted on a plastic bracket?

[rich weyand]

Why would a switch need to be connected to ground. The blower motor needs to be connected to ground.

The battery is connected to ground (the chassis). The other side of the blower motor is connected to ground (the chassis). That is, one side of the blower motor is connected directly to battery ground.

The switch only controls the hot side.

[ZXT]

I understand where you're coming from, but what would the switch do if all four wires leading to it had voltage?

It's like a toggle switch leading to, say, an electric fuel pump. One side of the switch has voltage, and once you flip the switch it closes the circuit and lets the current flow through the other wire to the fuel pump,which is grounded. If both wires leading to the switch had 12 volts, nothing productive would ever happen.

Maybe I'm wrong.

[rich weyand]

They all have the same voltage, but the resistance is different. The brown BAT wire brings full battery voltage to the switch. Whichever wire the switch selects has full battery voltage. And that flows through the resistors, and both of the other wires have voltage. What the switch does is select how much resistance there is in series with the blower motor, which limits the current through the blower motor. On HI, the resistor is bypassed by circuit 52A, and full current goes to the motor on circuit 52B. On MED, voltage is applied to the center of the resistor, flows through 1/2 of the resistor, and goes to the motor via circuit 52B. On LO, voltage is applied to the end of the resistor, flows through the whole resistor, and goes to the motor via circuit 52B. Since LO and MED work, the resistor is fine, the LO and MED wires are fine, and circuit 52B is fine. But somewhere, either in the switch, or the connector on the switch, or on the wire run through the firewall, or in the connection to the resistor, circuit 52A is broken.

[rich weyand]

Think of it this way. I have a water tap on the side of the house. I measure the water pressure as 60psi. If I put 500 feet of garden hose on it, and measure at the end, I get 60 psi. But when I turn the water on I get much less water out of the end of 500 feet of garden hose than I would if I was at the house right at the tap.

The resistor is 500 feet of garden hose. The three fan positions are LO (through the whole resistor, 500 feet of garden hose), MED (through half the resistor, 250 feet of garden hose), and HI (bypass the resistor, straight from the tap).

52A (black w/orange or orange wire) is the wire that bypasses the resistor. It's busted somewhere, or that position is broken in the switch. Only way to get what you are seeing.

[ZXT]

There is not a single black with orange wire on the pickup. Your scenario has the resistor in the equation, while mine doesn't. Are you talking about the four wires going to the resistor? Only two of those have voltage to them. My blower also has four positions.

[rich weyand]

OK, give me a little more info. I'll have to track this back from your end since we're not matching the print I am looking at. Lessee if I can find the print that matches you instead.

It's a 77, right? Model number (K5, C20, etc)?

Does it have A/C?

What color is the wire coming out of the blower motor? Should only be one wire.

At the first place that connects -- relay, whatever you want to call it -- what are the colors of the other wires connected there?

Let's start with that. You may have one of the optional setups, which are slightly different.

[ray_mcavoy]

ZXT, you mentioned a relay earlier ... was your 83 originally equipped with air conditioning? If so, trucks with AC did use a relay in the blower motor control circuit. And the diagram is shown on page 14 of the PDF file that Rich posted earlier in this thread.

Looking at that diagram, I can see a couple of things (aside from the switch & resistor that you've already replaced) that could prevent the blower from working on the lower speeds but still allow it to work on high.

One would be an open in circuit #101 ... the dark blue wire that connects the resistor assembly to the relay. That could be due to corrosion on the terminals or possibly a broken wire.

The other potential problem could be the relay's N.C. (normally closed) set of contacts that connect circuit #101 (dark blue wire) to circuit #65 (purple wire) leading to the blower motor. Those contacts route power to the blower motor for all speeds except high.

[rich weyand]

ZXT isn't the OP. ZXT's problem is that everything works EXCEPT high.

[ray_mcavoy]

Originally Posted by rich weyand

ZXT isn't the OP. ZXT's problem is that everything works EXCEPT high.

Hmmm ??? ... I thought ZXT was the OP here with an 83 C20 and a blower that was only working on high. And that gramps77 was the one with the opposite problem of the blower working on everything except high.