1972 C3 AC help needed

[J W.]

good afternoon. i need help and or suggestions for my ac problem.
the ac hi speed fan will not work. i have tested the fan switch and intalled new switches on the control in console. i have 12v. coming to the hi speed relay from the dk blue wire( hi-speed) of console fan switch. the orange wire from horn relay maintains a constant 12 volts. i have 2 new relays , one a usa made and one a china made . i removed the covers to inspect their operation . when fan switch is turned to hi speed(dk blue wire) the points in both new relays make contact. I have 12v on dk blue wire and 12v on orange wire, but 0 volts on purple wire to fan. note: ac is turned to max air on console. I can take the 3 wire plug off the relay and jump the blue and purple and the fan runs on highest speed. note all operations were performed with ignition on , but car not running. also ac compressor does work and fan works in all the other speeds. anyone experienced this or I am unlucky to have two bad relays. I'm exhausted!

[Edward J.]

Re: 1972 C3 AC help needed

Brian, sure sounds like a relay issue. sometimes you can clean the points (with a small file or sand paper) inside the relay by removing the cover, there are a few tangs that need to be straighten to remove cover. you should also be able to close the points by pushing them closed manually after you clean them. Make sure the key is off before you clean.

[J W.]

Re: 1972 C3 AC help needed

I have tested them both with cover off. the points are new. I have cleaned points the points also. the only thing I notice is that the china made coil gets very warm when energized and the usa made does not. neither coil when energized by the switch sends voltage to purple fan wire . unless anyone knows a reason that would cause the coil to not function I will spend another 20.00 on a coil.

[Harmon C.]

Re: 1972 C3 AC help needed

Have you checked the in line fuse behind the master cylinder . It controls the blower high speed.

[Edward J.]

Re: 1972 C3 AC help needed

I have tested them both with cover off. the points are new. I have cleaned points the points also. the only thing I notice is that the china made coil gets very warm when energized and the usa made does not. neither coil when energized by the switch sends voltage to purple fan wire . unless anyone knows a reason that would cause the coil to not function I will spend another 20.00 on a coil.

I would take a close look at the electrical connecter(3wire)and see if the plastic area around the purple wire looks like it may have got hot sometimes the connector get hot and will not make a connection due to connector expands from heat. Also if you hear the relay click on with the high speed selected on switch, this is a indicator that the switch and wiring to relay are good. the only thing at this point is the purple wire that feeds the motor from relay, you can also wiggle the purple wire at relay and see if the motor runs when doing this. that is a sure sign you have a connector/connection issue.

[J W.]

Re: 1972 C3 AC help needed

Update. never use a digital meter to check dc voltage. orange wire from horn relay read 12volts , but when switch engaged relay the voltage was not enough to power fan. problem was the fuse in orange wire tested good for continuity but would not give a full 12volts under a load. replaced fuse and cleaned holder, worked like new. thanks to all.

[Richard G.]

Re: 1972 C3 AC help needed

The digital meter read correctly and you would have gotten the same readings if you would have used a analog meter.
When the load (fan) was started you had a large voltage drop because of the extra current from the load.
If you can always measure voltage with the load connected.

[Harmon C.]

Re: 1972 C3 AC help needed

Right again the hidden fuse holder.