Topic: 65 Factory Underdash AC - Main Electrical Lead to AC Suddenly Has No Power

[rocket289k]

I'm chasing down a strange problem  The fan switch for the factory AC suddenly doesn't turn on the fan nor does it trigger the compressor clutch to engage.  It's like the main electrical lead has no power.  I disconnected the yellow main lead (which has the 15A fuse) to see if there is power coming from the ignition switch and there doesn't appear to be any power (the fuse is fine). 

The AC has been functional well since the restoration (new AC blower included).  I'm not sure why all of a sudden it started having an issue.  Could there be an issue with the iginition switch?  Everything else appears to be normal.  Car start and turns off properly, all other accessories run fine.  Thoughts? 


Ron

[67gtasanjose]

Yes, check the connection to the ignition switch. It might be easier to drop the switch out of the dash. Do you know how to pull the tumblers & unhook the switch bezel?

[C5ZZ]

You could check the post on the back of the switch for power with a test light
(when its in the on position). Might be a little difficult to get at, you may need
to take the evaporator loose to make room.

[jwc66k]

You could get a 66 Mustang Electrical Assembly Manual and look at the wiring diagram for the A/C circuit that shows the same post on the back of the ignition switch also powers the heater fan. With the power on and if the heater fan works, the switch should be OK. With that determination, the problem would be inside the A/C under the dash.
Jim

[midlife]

I've seen some in-line fuse holders fail continuity when the springs break due to corrosion or simply fatigue. Sometimes the fuse is simply too short and fails to make contact with the inline plugs.   Sometimes the pin tips need to be re-crimped to gain back continuity.  I've rarely seen a ring connector that goes on back of the ignition switch fail or the post itself fail.  If the latter happens, you'll get no accessory power anywhere in the car. 

[rocket289k]

Midlife wins the prize.  I found the problem earlier this afternoon (prior to reading Midlife's post) and it was indeed the in-line fuse connector.  Given the poor connection of the fuse on the "non-spring" end it's a miracle it ever worked.  I'll caulk it up to another crappy reproduction harness.  The wires themselves were fine but the in-line fuse connector itself was a "hot mess" / "el cheapo" part.

As result, I bought a much better in-line fuse holder (better design with end caps that completely surround the end tips of the fuse as opposed to trying to make connection with just the top of the fuse tips), cut the wires, re-crimped and soldered in the replacement connectors harvested from the replacement in-line fuse holder I bought today and presto - all better.  Thanks all for your ideas.

Diagnosis Procedure + Repair

- removed dash to get better access to the wires
- tested power to the back of the stud on the ignition switch (good)
- tested power in the wire lead from the ignition switch stud to the "hot" side of the fuse holder (good)
- tested power in the wire lead from the ignition switch stud (in-line fuse connected) to the "fused" side of the fuse holder (no power)
- used another fuse to ensure current fuse wasn't bad but not blown (fuse was fine)
- used a jumper cable to link the hot lead from the ignition switch to the wire lead to the AC unit (fan turns on as expected)
- buy new in-line fuse holder
- Macgyver new in-line fuse holder into existing wiring harness
- test connection / fan now works and shake head at crappy in-line fuse holder that was in that harness

I hope everyone had a great Father's Day.

Regards,

Ron

[67gtasanjose]

  COOL  Now your Chillin!