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Probably the best place to pick up the A/C wiring is in the service manual. The 72 wiring is a little unique because the high speed wire comes off the horn relay on the firewall.
 

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Discussion Starter #3
<BLOCKQUOTE>quote:</font><HR>Originally posted by John_Muha:
Probably the best place to pick up the A/C wiring is in the service manual. The 72 wiring is a little unique because the high speed wire comes off the horn relay on the firewall. <HR></BLOCKQUOTE>

My problem is I only have high blower. I've changed the relay switch ( twice ), and tried 2 blower switches and can't get any blower speeds except high. Does the blower relay feed off of the horn relay?
 

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High speed only is off the horn relay. That runs from that orange wire across the firewall. The lower speeds come off a brown wire from the fuse block. First check the fuse. I assume you did already but I'll mention it. Since you have changed the switch and the relay I'll assume it's not either of them. Have you tried measuring power to ground on the relay terminals when the switch is in the lower speeds? You have it on the orange wire but what about the other wires?
 

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Discussion Starter #5
<BLOCKQUOTE>quote:</font><HR>Originally posted by John_Muha:
High speed only is off the horn relay. That runs from that orange wire across the firewall. The lower speeds come off a brown wire from the fuse block. First check the fuse. I assume you did already but I'll mention it. Since you have changed the switch and the relay I'll assume it's not either of them. Have you tried measuring power to ground on the relay terminals when the switch is in the lower speeds? You have it on the orange wire but what about the other wires? <HR></BLOCKQUOTE>
That's why I needed a schematic, of the wires to the relay. Doesn't that relay have 2 hot leads going to it?
 

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Yeah, easier with a schematic. In the meantime, the relay has 3 hot wires on it.
Orange is always hot. Runs the blower in high mode.
Purple is the + output to the fan.
Dark blue comes from the switch. Guessing that you have no power on this wire. Perhaps it is the resistors than opened. These are located in the front of the box, under the hood, about 12 inches away from the relay.
 

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Tony, I believe that all of the information everyone has given you thus far is correct. I'm in the middle of repairing/replacing/updating the wiring and entire A/C-heating system on my '71 Camino. The wiring is very similar if not exactly the same. I've spent a couple of weeks now comparing the harness to the factory wiring diagram. A lot of the ways that the factory engineers routed the wiring doesn't always seem to make the most sense but I guess you have to remember that it was 1969 or 70-something and that things like relays were much less dependable and expensive (from a production and warranty point of view) so the engineers tended to stay with some kind of fail-safe version of a back-up. In your case (or, all of ours I suppose), the ventilation system would be a big issue if it completely failed. The factory engineers wired the high speed position of the blower motor separately from the other speeds so that you would be less likely to have absolutely NO ventilation versus some. To solve your problem try checking these things:
Verify that ALL fuses are good with a test light or an ohm meter, NOT VISUALLY.
You have verified that your blower motor relay works because you only have HIGH fan speed. The other three speeds, lo, med, med-hi, are all controlled separately by power which begins at the fuse panel heater fuse, through a brown wire to the A/C-heater control panel. You didn't say whether you have A/C or not but that won't matter up to this point. The brown wire will connect to the master switch if it's an A/C car. The master switch is only off if the upper control lever is all the way to the left in the 'OFF' position. From here it continues to the no.1 terminal on the back of the blower speed switch. In the 'HIGH' position voltage is only supplied from the blower switch to the blower motor relay and from there, directly to the blower motor. This all seems to work on your car. Your problem has to be in the wiring that goes from from the back of the blower speed switch, through the firewall grommet, to the blower motor resistors. First check the wiring on the back of the blower speed switch, it's often melted. If that's OK then turn the ignition to 'ON', set the blower speed switch to 'Lo' and check for voltage at the yellow wire that goes into the connector that connects to the blower motor resistor located in the heater-A/C suitcase in the engine compartment. The connector is a 4 wire connector arranged in a 'T' shape. The yellow wire should be the one on the bottom. Don't disconnect it, just use a sharp probe to get to the connector crimped onto the wire from the back side. While you're right there, check for voltage at the purple wire which is the upper right cavity as you view it leaning over the fender. If there is NO voltage at the yellow wire, either the blower speed switch is faulty or the wiring between the speed switch and the blower resistors is faulty. If there IS voltage at the yellow wire BUT NOT at the purple wire, then the blower resistor assembly is faulty. The blower resistor assembly is a pretty tough piece, electrically speaking, the wires will usually melt before this thing does.
Hope this helps.
P.S. Sorry about the lengthy explanation, I realize how frustrating something can be when you don't have enough, or the right, information.
Louie Hammel
 

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Discussion Starter #8
Thanks Guys! That should be all the information that I need to trace this out. I'll post the result as soon as I can get to work on the car.
Tony
 

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Tony, I gave you some wrong information in my last post. Here's the corrections. The connector attached to the blower motor resistors is a molded connector and can't be probed from the backside. The spade terminal arrangement is in the shape of a 'T' but the wires exit the connector aligned vertically. The top wire is not purple, it's a dark blue 10 ga. that runs only about six inches until it splices into the 10 ga. purple wire that goes directly to the blower motor. You can still check voltage at the yellow wire which is the bottom terminal on the blower resistor by pulling the connector back just enough to expose the spade terminal but not enough to disconnect it. Check the 10 ga. dark blue wire by unwrapping the splice at the 10 ga. purple wire about six inches back.
Sorry if I may have caused any confusion.
Louie Hammel
 
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