Automotive Air Conditioning Information Forum (Archives)

bigcoaxum on Wed June 22, 2011 10:18 PM

Year: 1973
Make: Chevrolet
Model: Impala
Engine Size: 350

I have a 1973 Impala and the A/C only blows on high. I changed the switch and the relay and it still blows on high. i think the wiring has been tampered with because some of the wires were not in a harness like they are suppose to be. I ordered a new harness and the wires on the harness are yellow, orange and black. the wires coming from my car are orange, blue, and looks like red. there are a total of 5 wires that connect to the relay but the bottom two are connected to a pigtail so i'm not too concerned with them. Its the top 3 wires that were not connected to a pigtail that i'm concerned with. does anyone know how to wire the blower relay the correct way so the my switch will blow on all 4 speeds? Pictures would be very helpful and all comments.

thanks

mk378 on Wed June 22, 2011 11:15 PM

Did you find the resistor yet? Speeds other than high go through a resistor (prone to burn out), unless it has a multispeed motor (more than 2 wires on the motor).

bromodragonfly on Wed June 22, 2011 11:55 PM

Here's a diagram with the resistor pack that MK was talking about:



I don't know if this diagram accurately represents what's in your car. But it's a common method of electrical speed control.

Settings low, med, high, will route current through resistors in series. Low will create the most voltage drop before current hits the motor, creating the lowest speed.

Max speed will create a pathway through the coil on the relay, which will magnetize and pull the relay contacts closed. Then 12v will be able to flow directly through those contacts and to the blower motor. Since you mentioned you had 4 speeds, this may be how yours works.

If low med and high don't work, the last resistor in series is probably burned out. If blower blows max on all settings, then current is bypassing that resistor pack somehow. Maybe the blower wasn't working at all before, and someone ramrodded the wiring because they were too lazy to trace down the issue.

Anyway, if your relay operates the same as the one in the diagram, one terminal will be connected to the max switch, one will be 12v power in, and one will be 12v power out. 12v in and 12v out should have no continuity until 12v is applied across the coil. If 12v is applied across the coil, you may hear the contacts snap closed.

There's only one winding in the motor, two of those wires will connect power across it. I'm not sure what the other one is for. Maybe it sends a signal to something else when the blower motor is running. You could ohm between the wires to see which ones go across the winding.

Here's a picture of a resistor block, sorry, crappy quality:



Hope this helps a bit..... I couldn't find a wiring diagram or any other info for your car

I could be horribly wrong here also. DC in cars is not my forte.

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There is no knowledge that is not power

Dougflas on Thu June 23, 2011 5:32 AM

I have the wiring diagram for this vehicle. I should have the OEM factory manual. If you don't find the info you need, email me and I'll get it to you. email is dktv at aol dot com It would take me a day or so to locate the manual. The high speed relay pin color purple feeds the resistor if that helps.

bigcoaxum on Thu June 23, 2011 8:09 AM

I'm having trouble determining what the resistor is. I'm confused. is the resistor the same as the switch? I went to autozone and i was told that the switch and the resistor is the same thing. what does the resistor look like? Also, where is the resistor located? I'm clueless..

Edited: Thu June 23, 2011 at 8:26 AM by bigcoaxum

mk378 on Thu June 23, 2011 8:13 AM

The resistor is not the same as the switch. Resistors are like the picture Dragonfly posted. It's going to be flange-mounted on the ductwork near the blower with the coils inside the duct. You will only be able to see the terminals and plug from the outside.

Edited: Thu June 23, 2011 at 8:16 AM by mk378

bigcoaxum on Thu June 23, 2011 8:29 AM

Do you have any pictures of this location? I understand what you are saying but i'm clueless about the location. Do you mean the ductwork under the dash? I have no idea where the blower motor is. i was told that it is located behind the fender well out of sight.

Dougflas on Thu June 23, 2011 5:54 PM

Wiring schematic is on its way to youvai email. Also, look for an inlineplastic 30 amp fuse at the rear of the firewall to the left of the distributor of a V8 engine. The input is red wire that goes into the fuse holder. the wire then exits as an orange wire. Well known to be bad back then. It caused blower speed problems.

bromodragonfly on Thu June 23, 2011 6:03 PM

Here's the Chilton's procedure for replacing the blower. Hopefully it gives you some idea of what and where they're talking about:

Disconnect the negative battery cable.
Disconnect the hoses and wiring from the fender skirt.
Remove all fender skirt attaching bolts except those attaching the skirt to the radiator support.
Pull out, then down, on the skirt. Place a block between the skirt and the fender.
Remove the blower-to-case attaching screw. Remove the blower assembly.
Remove the blower wheel retaining nut and separate the motor and the wheel.
Install the blower wheel on the motor and secure the retaining nut.
Position the blower motor assembly to its mounting. The open end of the blower should be away from the motor. Install the retaining screws.
Install the fender skirt. Connect the required hoses and electrical wiring. Connect the negative battery cable.

The picture from my last post that shows the resistor pack is supposed to be from a 1973 Impala. As is this one:



You can see the wiring harness that connects to the motor. There should also be a separate harness nearby that plugs into the resistor pack.

good luck

-------------------------
There is no knowledge that is not power

bigcoaxum on Thu June 23, 2011 8:22 PM

thanks guys. I found the resistor and ordered a new one and got the relay wired up. i'll wait on the resistor to see if my speeds work the right way.

chuckwp on Fri June 24, 2011 8:58 AM

Quote
Originally posted by: bromodragonfly
Here's the Chilton's procedure for replacing the blower. Hopefully it gives you some idea of what and where they're talking about:



Disconnect the negative battery cable.

Disconnect the hoses and wiring from the fender skirt.

Remove all fender skirt attaching bolts except those attaching the skirt to the radiator support.

Pull out, then down, on the skirt. Place a block between the skirt and the fender.

Remove the blower-to-case attaching screw. Remove the blower assembly.

Remove the blower wheel retaining nut and separate the motor and the wheel.

Install the blower wheel on the motor and secure the retaining nut.

Position the blower motor assembly to its mounting. The open end of the blower should be away from the motor. Install the retaining screws.

Install the fender skirt. Connect the required hoses and electrical wiring. Connect the negative battery cable.



The picture from my last post that shows the resistor pack is supposed to be from a 1973 Impala. As is this one:







You can see the wiring harness that connects to the motor. There should also be a separate harness nearby that plugs into the resistor pack.



good luck

That picture of the blower motor is NOT from a 73 Impala. The blower goes through the firewall up behind the fender liner on the p side of the car.