I am getting ready to bring my 73 BB to the shop tommorrow for A/C system flush , vacuum test and R134 load. I've installed a rebuilt (dry)compressor, and a new dryer, using new green o-rings. I've removed the blower motor, checked with my hand for debris inside around the evaporator, rewired blower so I now get 4 nice speeds. Condenser looks ok.

The wiring harness connector going to the compressor has a green and black wire. Black is obviously ground. Green is wired to what appears to be another connector closer to the firewall, with what I think is some type of resistor with three prongs, that plugs in. It is labelled 'A' 'B' 'C' .On this connector is a circle clamp, like it is supposed to be secured onto a half-inch hose or the like . . the resistor itself, unplugs and is labelled 'A' 'B' 'S'

When I switch on the A/C from inside the car I get 12v onto the middle prong of the resistor, but no 12v going out to the green compressor connector. The resistor seems to be electrically open between the middle connector and the other two on the ends, which are shorted.

My Hayes wiring diagram does not seem to have any of this wiring in it.

My questions are,

1) What is this resisitor thing ?

2) Can I safely by-pass it and connect the switched 12v to the compressor?

3) WHICH TAB on the compressor , of the two there, gets the 12v green wire , and which gets grounded? If you know this answer , reference it from looking at the front of the compressor viewing the clutch and pulley . . . is lt left or right? Can someone with a similar C3 and A/C go look for me? A picture would tell a thousand words . . .

When I got the car all this stuff was disconnected !

Thanks . . . . .

 

If you are standing in front of the car looking at the windshield, it is the prong on the intake manifold side. The other prong is the one closest to the right fender.

What did you do to your blower motor to give it four speeds? Could you tell a big difference in the car?

 

Thanks. I called the guy who will leak test tommorrow, he said the resistor is probably a heat-sensitive saftey cutoff to save compressor burnout.

The 4-speed fan tweak, really helped. Blows like crazy now. Heres what I did:

1) if you look at wiring diagram you will see the heater resistor assembly in the blower circuit. Its mounted on the firewall side of the heater box inside . . . forget getting to that unless you need to change the heater core. The resistor acts as a voltage divider. The fan switch under the console, takes a 12v feed, and depending on which setting, distributes it to the 4 terminals of the resistor assembly, which is nothing more than 3 separate coils of wire connected in series, with two connection points in between and one on each end, for a total of 4. There are therefore 4 terminals on the resistor.

2) I figured my wiring was old and dropped alot of the 12v along the way, and that the resistor was old and out of calibration. It also seemed like I had only three speeds, wheras the switch has 5 positions, 1 for off and 4 for lo, med, med-hi and hi. I had no hi. and lo and med-lo were the same.

3) First I purchased a new resistor from Eckerts for 18 bucks. When it came it was huge, and I realized it was un-reachable anyway without pulling the heater box. So I measured the coils, each one was just under 1 ohm.

4) Went to Radio Shack and purchased 6 1-ohm , 10-watt power resistors for like a buck apiece. I took two and wired them in parallel to give me half an ohm, 20 watts. Did the same with the other 4 in sets of two. I then took each pair and wired the 3 pairs in series. So I had the same 4 connections. Starting from the top, #4 was 12v, #3 11.5, #2 11 , #1 10.5 v

5) Using the wiring diagram , I cut the corresponding 4 wires coming from the fan speed witch under the console, and soldered them to the 4 points on my new resistor pack. I used heat-shrink, and tucked the whole thing out of the way under the console.

6) Last thing I did was run a new wire from the #4 point on the new resistor pack, which corresponds to hi fan speed, thru the firewall and to the blower motor.

If you're confused on all this, email me, and i will email you back a schematic. Its pretty straight forward.

So now I have all 4 speeds, and hi speed blows like crazy, I get tons of air coming out of the two center vents and the 2 ball vents on the side.

If you want to see how much blower power you could get, disconnect the blower motor power connector, its got a black rubber boot. Then attach a separate wire connected directly to 12v from the battery ( I used the 12v supply to the alternator). This puts 12v directly to the blower motor, and it will jump to full speed without dropping any voltage on old wiring.

 

The plug in fuse works like this: One terminal goes to the super heat switch located in rear of compressor, if this switch closes to ground, it "heats" a resistor in that "plug-in" fuse block, thus tripping the fuse which opens the 12v from second terminal (which continues on to clutch). Which interupts power to compressor clutch. Remaining terminal is 12 volts "in" . :thumbs: