Experienced an A/C issue over the summer and haven't posted it to ask for advice until now. It seems that when I turn the A/C on in the car it works for the low and medium setting, but when I select the high setting it shuts off. Any ideas on what might be going on with it? I cycled through it a few times, from off all the way to high and had the same problem over and over.

Thanks.

 

The high speed blower relay gets direct battery power from the fusible link at the starter in most cases. Verify voltage at the relay; it's usually attached to the heater box.

 

Actually on Rick's 1969 the high speed blower relay is on the firewall, above the master cylinder. High speed gets power from a 30A fuse in the harness from the horn relay junction block. There is also a compressor clutch relay on the passenger side fender but that has no connection to the blower motor.

 

Also, AC is both running the compressor and the fan. OP can check fan behavior in vent and should be exactly the same. Should be a very short fuse in inline holder as mentioned by Joe. Although fuses should be indicators of larger problems, like shorts, sometimes they are just gone, especially in a bumpy environment.

 

I lost the high speed fan due to corrosion in the fuse holder. It was so bad that it crumbled in my fingers as I was working on it.

 

I've seen that problem before as well.

 

Sounds like a bad design.
Are those fuse holders still available as a wear item?

 

None of the electrical connectors GM used in the 1960s are particularly robust, but keep in mind that these cars were only intended to last 10 years/100K miles. No one expected them to be around half a century later. The Weatherpack connectors that replaced the Packard 56 series are environmentally sealed and work a lot better, and now the Metripack and Packcon systems have replaced those, given how dependent modern cars are on the electronics. Certainly you can splice in an inline fuse holder, but it won't be optically correct.

 

Deutsch connectors are much easier to work with, even though they're Frod and Harley spec.

 

I have no experience with those, but with the correct crimping tool, Weatherpacks are easy.

 

I have fixed many cars with this issue using a ATO fuse holder.



Les than 10 bucks at Napa.


Obviously not 100% “correct” but a much better design than the factory fuse and holder.

Another possibility, the blower fan could be pulling excessive current. Maybe not enough to pop the fuse, but enough to cause wiring to get hot. If you could find a shop with a clamp on style inductive ammeter you could easily test it. Blower motors (any electric motor for that matter) draw much more current at start up, once they are running I wouldn’t think they would pull more than 15-20 amps tops. If it’s much more than that, inspect the wiring, grounds, and the motor itself.