Strange issue on this one. We helped a customer re-install the underhood AC components on his 1970 XR7 hardtop. Found that the blower motor would not blow at all when in the “high” position. We installed a new resistor module and now it blows on high. The customer took the car home with the new AC working, but now reports that if he selects “hi” on the blower, the car dies out. It does have an after market MSD coil, and Mallory Uni lite distributor. Any ideas on what could be causing the problem? thanks, Scott
Battery voltage might be dropping too low to keep ignition system going. Blower takes lots of power on high, and alternator needs to be replacing what is drained from the battery. I would check battery, voltage regulator, and alternator.
Maybe put a multi meter on battery while running and see what the amps are reading. 13.5-14 should be correct reading.
Then turn on blower and see what the drop is.
Shouldnt be pulling that much to kill ignition I’m guessing
The XR7 will have an amp gauge. If it gets pegged at a normal RPM will heavy electrical loads like headlight, blower motor etc… it can indicate a charging issue. If it reads negative most of the time then the charging system can’t provide enough power for all the loads. Electrical loads like applying the brakes or turn signals should make it bounce around.
Yes, good idea. 13.5 - 14 volts (amps is measurement for current) at battery with engine running would indicate charging system is working. And if charging system is working this shouldn’t drop much when blower is turned on. But if charging system is not working, and/or battery is bad, the blower could drop battery voltage down below 10 volts causing ignition system dropout.
Isn’t there supposed to be a solenoid on the carb that kicks the idle up a notch when you turn on the AC?
Maybe that needs to be adjusted a smidge.