hot key problem in my '65 Riv

[Guest lotuslover]

My '65 Riv develops a hot (very hot) ignition key when I'm operating the A/C. The compressor is working as is the blower motor. All grounds are clean. The key is normal when operating the car without the A/C running.

[Jim Cannon]

All accessory power passes through the ignition switch when the engine is running. The contacts inside your switch are starting to get kind of dirty. This resistance generates heat when current passes through it. If you can find one, get a new switch. The ignition switch is separate from the lock cylinder that the key goes in, so you can replace the switch and not have to mess with changing out keys or lock cylinders.

[tim63riv]

Umm,

Actually increased current flow causes heat, not poor connections, they increase resistance to current flow! With the A/C on, you are supplying current to the compressor clutch and to the fan motor as well, both draw quite a bit of current when operating. The "hot" key could be a symptom of the problem but may not be the cause. As electrical components with windings in them like motors and compressor clutches get old, the insulation on their winding break down and the windings short together. The shorted windings actually reduce the amount of resistance in the component and causes the current through the device to increase during operation. Any inductive ammeter should help you to find the current hog in your electrical system!

HTH,

Tim

[Paul K.]

My 64 had the hot key problem about 20 years ago. I new a lot less mechanically then, took a guess and replaced the ignition switch. Fixed the problem. I found the switch at NAPA but again, this was 20 years ago.

[Guest lotuslover]

My '65 Riv develops a hot (very hot) ignition key when I'm operating the A/C. The compressor is working as is the blower motor. All grounds are clean. The key is normal when operating the car without the A/C running.

I failed to mention that I have replaced the ignition switch with a new one from CARS. Didn't change the problem.

I've also noted that the wires to the A/C compressor and the blower motor do not seem to heat up when the switch is hot. So what else in the system is pulling excess power--to the point of causing the switch to overheat? And how do you find it without tearing the dash apart??

[oldstyle]

Resistance does cause heat. Excessive resistance can be from a poor connection, wire size that is too small,etc.

[JZRIV]

All good suggestions. My experience with this symptom has been poor connections on the back of the switch where the wiring harness plugs in. I have replaced a few melted connectors because of bad connections.

I always clean those terminals up and squeeze the female connectors just a bit to make sure they fit tightly. A bad connection creates resistance and voltage drop in turn creating heat much like an incandescent light bulb. The heat accelerates the bad connection. The operation of unplugging and re-plugging when replacing the switch will loosen them up. There is little margin for error because as mentioned a lot of current flows through the switch. A bad connection generates much more heat with a larger current flow than say if the circuit was operating just a radio.

I would check the terminals as a first step if you have not already.

In my experience troubleshooting electrical circuits of all kinds, often times when you locate the hot spot, you have isolated the problem. Of course their are always exceptions. Check the wiring connectors to the blower switch, relay, etc and look for visual signs of excess heat.

If you have 100% eliminated the switch and connector, try running just the blower on high without the A/C on and see what happens and/or run the A/C with the blower on lowest setting. That might help narrow down the circuit with the problem.

Edited August 28, 2010 by JZRIV (see edit history)

[Guest lotuslover]

JZRIV,

Think I'd isolated the problem and it is a you described. The plastic connector on the back of the ignition switch has been trying to melt down. enuf where the connectors are no longer tight to the spade terminals on the ignition switch. My local wiring specialty shop will be fixing it next thurs. We can't find a NOS connector so it will just be individual connectors into the switch. I found it by measuring the temp of the switch and connector and the wires leading into the connector. With the a/c and blower running full-on, the temp of the connector and switch was over 145 degrees. No other connector or appliance was over ambient templ. Enuf heat was being generated to start melting the plastic connector. I suppose on the way to a dashboard fire, I'd guess.

Thanks for your post. It will be helpful to others as well.

b