Voltage levels dropping when AC turned on in my 67 GTX?

[AR67GTX]

I have a factory air 67 GTX that some may remember my adventure with last winter in switching over from an electronic voltage regulator to a mechanical one to get my system voltage levels down from 15+ volts to 14 volts. It took a new, rebuilt alternator in addition to the mech VR but I finally got everything squared away. Or so I thought.

I’ve been replacing the interior in the car this spring and summer and finally completed it this week. Backed the car out to run up to the corner and get some gas and thought I would kick in the AC to exercise it. When I did, my voltage gauge dropped from 14 to 11.5-12 volts. Reving the engine up or driving down the road didn’t change it significantly. Turning the AC off kicked the voltage up to 14 immediately. I have an idle solenoid on the engine wired to the compressor to kick the idle up a couple hundred rpm but it makes no difference. My dash charging gauge continued to show a slight charge during all of this. Cycling the AC off and on didn’t make much difference.

Anyone got any ideas on what’s going on with this? I’ve started the car numerous times to back it in and out of the garage while working on it for several months so I doubt my battery is fully charged. First thing I’m going to do is charge it. I may have to go back to that blasted electronic VR!

 

[AR67GTX]

Put the battery charger in it and the battery is nearly full scale although the green “charged” light is not quite on. So a discharged battery is not the issue.

 

[R413]

Must be above 1200 RPM when looking at the system voltage.

The alternator is to supply all the power for electrical system. Did it do this with the electronic regulator.

 

[AR67GTX]

Well deja-vu, doing a search and I had this exact same problem 12 years ago. Looks like back then cleaning my bulkhead connections fixed everything. I just cleaned them last year with De-Ox and lubed them up but if it worked last time, guess I need to try it again.

Charging problem

 

[AR67GTX]

Must be above 1200 RPM when looking at the system voltage.

What was the rpm?

I drove it down to the corner gas station. Didn’t get much speed up but sure that in 1rst it hit 1600 or so before going to second several times. Reved the engine a few times - no difference

I was cleaning it up to take to cruise night this evening. I’ll see if I notice any significant changes from that.

See my last post - has this problem 12 years ago and forgot it. Bulkhead connector then it seems. They are original but really clean. Maybe time for a new engine harness.

 

[AR67GTX]

Jeez, it was only Dec 2023 when I last cleaned them.

 

[AR67GTX]

Something as simple as pushing in and wiggling the bulkhead connectors didn’t help. I’ll dig into it some more next week. Seems to be something triggered directly by the AC button - voltage gauge takes an immediate 2 volt drop when pushed and when shut off the voltage immediately jumps back to 14. The fan operation doesn’t affect it at all. Guess I’ll trace through the AC compressor clutch wiring and connections.

 

[1 Wild R/T]

Unplug the blower motor and see what your voltage does... Blower motor can draw a lot of amps when the bushings go bad...

I see in your last post fan operation doesn't effect it.... But in your first post you mentioned cycling the A/C didn't seem to have much effect....

FWIW the A/C clutch is basically a direct short, the current is limited by the wire size & length... Unplug the clutch at the compressor & see if anything changes..

 

[Geoff 2]

The 'rebuilt' alt. I would be looking at that. Sounds like it's output is not enough with the load of the AC is added.

 

[AR67GTX]

Unplug the blower motor and see what your voltage does... Blower motor can draw a lot of amps when the bushings go bad...

I see in your last post fan operation doesn't effect it.... But in your first post you mentioned cycling the A/C didn't seem to have much effect....

FWIW the A/C clutch is basically a direct short, the current is limited by the wire size & length... Unplug the clutch at the compressor & see if anything changes..

If I implied cycling the AC didn’t seem to have much effect that was unintended. Pushing the AC button on is what causes the voltage to immediately drop. Although the AC does run. Switching the fan speed has no effect. I’m going to investigate the power lead to the clutch - sse if it has any unusual resistance.

One thing I want to check out - in the middle connector in bulkhead box on the firewall I pictured above, one of the second row bays either looks empty or the blade is shoved back. I need to see if that bay and circuit (if it’s not empty) has anything to do with AC.

 

[AR67GTX]

The 'rebuilt' alt. I would be looking at that. Sounds like it's output is not enough with the load of the AC is added.

Hmm - second one I’ve gotten through a member who used what he considers a reputable builder. Seems to work well. Lights on and off don’t seem to cause any unusual voltage issues. But I still have my prior alternator that worked, just not well with an mech VR. If I don’t find some other issue I can try swapping it back in to see.

If I implied cycling the AC didn’t seem to have much effect that was unintended. Pushing the AC button on is what causes the voltage to immediately drop. Although the AC does run. Switching the fan speed has no effect. I’m going to investigate the power lead to the clutch - sse if it has any unusual resistance.

One thing I want to check out - in the middle connector in bulkhead box on the firewall I pictured above, one of the second row bays either looks empty or the blade is shoved back. I need to see if that bay and circuit (if it’s not empty) has anything to do with AC.

View attachment 1690218

Looks like this is probably the problem. It’s the “P” bay in the bulkhead. That circuit runs to the Battery side of the alternator. It’s loose in the bulkhead and probably the load of the AC is more than the weak connection can handle, screwing up the signal to the alternator - my guess. Problem is that under-dash access to the bulkhead connector looks to be virtually impossible without taking loose the AC/heater box which I’m loath to do.

Probably got a weaker connection after I cleaned them last Dec. I haven’t run the AC since then.

I can pull the female connector almost out of the bulkhead but so far that and trying to search the underside of it for the locking tang with a small screwdriver to open it up so it will lock, has been beyond my coordination. I’ll keep trying.

Any other suggestions are welcome.

 

[RJRENTON]

I have a factory air 67 GTX that some may remember my adventure with last winter in switching over from an electronic voltage regulator to a mechanical one to get my system voltage levels down from 15+ volts to 14 volts. It took a new, rebuilt alternator in addition to the mech VR but I finally got everything squared away. Or so I thought.

I’ve been replacing the interior in the car this spring and summer and finally completed it this week. Backed the car out to run up to the corner and get some gas and thought I would kick in the AC to exercise it. When I did, my voltage gauge dropped from 14 to 11.5-12 volts. Reving the engine up or driving down the road didn’t change it significantly. Turning the AC off kicked the voltage up to 14 immediately. I have an idle solenoid on the engine wired to the compressor to kick the idle up a couple hundred rpm but it makes no difference. My dash charging gauge continued to show a slight charge during all of this. Cycling the AC off and on didn’t make much difference.

Anyone got any ideas on what’s going on with this? I’ve started the car numerous times to back it in and out of the garage while working on it for several months so I doubt my battery is fully charged. First thing I’m going to do is charge it. I may have to go back to that blasted electronic VR!

There is no such thing as a "new rebuilt" alternator......it can be either NEW or REBUILT but not both. The problem with a "rebuilt" alternator is....you never know what was done to it. Likely brushes and bearings were replaced but what about the diodes or stator windings or rotor? Were they tested...to what criteria. It is unlikely that the place you bought the "new rebuilt" unit from will know....but ask.....if they cannot answer, pass. Shop around.......just my opinion of course.....
BOB RENTON

 

[AR67GTX]

New to me. Rebuilt for someone else. But that’s not the issue if you read further down.

 

[1 Wild R/T]

I think you can remove the bulkhead connector to get better access... just release the four spring tabs, push it in, go under the dash and pull it toward the drivers footwell... I did it years ago on my 70 Charger that had A/C

 

[kiwigtx]

I have a factory air 67 GTX that some may remember my adventure with last winter in switching over from an electronic voltage regulator to a mechanical one to get my system voltage levels down from 15+ volts to 14 volts. It took a new, rebuilt alternator in addition to the mech VR but I finally got everything squared away. Or so I thought.

I’ve been replacing the interior in the car this spring and summer and finally completed it this week. Backed the car out to run up to the corner and get some gas and thought I would kick in the AC to exercise it. When I did, my voltage gauge dropped from 14 to 11.5-12 volts. Reving the engine up or driving down the road didn’t change it significantly. Turning the AC off kicked the voltage up to 14 immediately. I have an idle solenoid on the engine wired to the compressor to kick the idle up a couple hundred rpm but it makes no difference. My dash charging gauge continued to show a slight charge during all of this. Cycling the AC off and on didn’t make much difference.

Anyone got any ideas on what’s going on with this? I’ve started the car numerous times to back it in and out of the garage while working on it for several months so I doubt my battery is fully charged. First thing I’m going to do is charge it. I may have to go back to that blasted electronic VR!

Have you never been in a nice hot shower at home when someone flushes the toilet, and someone starts up the washing machine?

Same principle. Flow rate vs volume.

 

[AR67GTX]

I think you can remove the bulkhead connector to get better access... just release the four spring tabs, push it in, go under the dash and pull it toward the drivers footwell... I did it years ago on my 70 Charger that had A/C

I think I can pull the steering wheel and the instrument cluster, pop the bulkhead loose and have access through the opening to carefully switch the wires to a new bulkhead connector. I need to make sure I don’t have any melted wiring like my 66 had that required a new harness. But I haven’t smelled anything burning or seen any smoke so I don’t think I do.

 

[Geoff 2]

I don't think you have a wiring issue if you are getting 14 v with AC off. Not sure how much current the Chrys AC compressor draws, but they all draw a hefty amount. I think your re-built alt is the culprit. It is not producing enough amps at low rpms to charge battery with the AC on, hence the low voltage reading.

 

[HEMIB]

What's the voltage at the battery versus the voltage inside the cab maybe the battery is actually charging & you have volt drop between the battery & the internal wiring