C2 Ammeter Odd Readings

[Peter L.]

I had an after market (Vintage Air) A/C system installed in my 63, and my ammeter is reading weirdly. With system off, everything is normal. When I turn the system on, as I increase the A/C fan speed, I would expect the ammeter to either stay at zero, or possibly go negative (I had the alternator rebuilt with 75 amp capacity, so it should handle the extra load of the Vintage Air system). Instead, the ammeter goes positive. From about 5 amps at low fan speed, to about 20 amps at max speed. I have since had an electric fan for the condenser/radiator installed, and that and the A/C drives the ammeter to 40 to 50 amps positive. Again, with them off, everything works fine. (ie, start the engine, ammeter goes negative while cranking, the positive after engine starts, then down to zero. With engine off, headlights on, shows negative.) As a side issue, I've been told I need to get a larger alternator (100 to 140 amps, with built in regulator) to handle the load of both the A/C and fan additions. Currently the A/C power line is connected to the solenoid, as per instructions, and the fan is connected directly to the alternator output, so it's current is no longer reflected in the ammeter. Anybody got any ideas on what this could be, or how to test to find the cause of this?

[Frank D.]

Re: C2 Ammeter Odd Readings

If you hooked up the A/C system's main power to the battery per the instructions its a mistake.
C2 Corvettes use remote voltage sensing and so you need to draw the main power off the horn relay buss...your ammeter won't read right and the system won't charge properly if large power draws are taken from other locations.

Spend some time on the Mad Electric web site technical pages if you need more explanation...

The original 63 A/C alternator, a "633" was 52 amps IIRC (rare and expensive), you can have your original 628 alternator internally upgraded to 70 or even 100 amps and things will be fine. Mine has been upgraded to 100 amps but a previous one was done to 70 amp output and I had no charging problems at all...

Some will tell you your wiring wasn't meant to handle that much current but you will never see peak loads like that.

If you PM me your email address I can send you a list of tips I put together for installing Vintage Air A/C; some of which are generic but many are 63-specific. The file won't upload to this web site for some reason.