Blown88GT
Founding Member
That disconnects the electric clutch from the compressor, therefore compressor is free wheeling.
Engine Car stalls when going to a stop with the AC on
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Blown88GT
Founding Member
I have a similar issue/thread, but mine is a little more hectic....Most recent tests show that when my AC, headlights, and rear defrost are on it drains my battery from 14.5 volts at idle to below 13volts into an ugly stall.
Curious what the correct amp draw and voltage drop with the AC at idle should be? I am dumping power and amps somewhere. Its exactly the same results just the AC and the headlights on. How are you measuring amp draw?
Curious what the correct amp draw and voltage drop with the AC at idle should be? I am dumping power and amps somewhere. Its exactly the same results just the AC and the headlights on. How are you measuring amp draw?
Well, my meter 
the bed. Tried to take measurements this AM but it's not working. It's a clamp on style meter than can read D.C. Amps with a 40 and 400 amp range
If I remember correctly my car idling with the e fan off and nothing else on was maybe 40-50 amps tops...if that. If I turned everyone on I was maybe 80-90 amps tops. All off memory though so I could be slightly off.
Ac compressor really doesn't add much load. Your are just locking the clutch.
the bed. Tried to take measurements this AM but it's not working. It's a clamp on style meter than can read D.C. Amps with a 40 and 400 amp rangeIf I remember correctly my car idling with the e fan off and nothing else on was maybe 40-50 amps tops...if that. If I turned everyone on I was maybe 80-90 amps tops. All off memory though so I could be slightly off.
Ac compressor really doesn't add much load. Your are just locking the clutch.
No where here have I seen a battery test. I don't know what effects a bad battery would have on amp readings but I would have it checked anyway just to rule it out if you have not done so.
i don't have much faith in parts store testing procedures, they are not mechanics, they mean well but lack the training for complete diagnostic procedures. A high amp draw at idle would be a red flag to me and would need further investigation. That may be causing or at least contributing to your problem.
i don't have much faith in parts store testing procedures, they are not mechanics, they mean well but lack the training for complete diagnostic procedures. A high amp draw at idle would be a red flag to me and would need further investigation. That may be causing or at least contributing to your problem.
Blown88GT
Founding Member
Good point. A bad battery could add to the current draw. Battery cells can short internally & the alternator attempts to charge a battery which won't charge. BTW, charged battery measures 12.6 VDC, each cell is 2.1V * 6 cells = 12.6V
Blown88GT
Founding Member
At 13V, battery is not being drained, but alternator is having a problem keeping up with the load.
Rear defrost is probably the biggest load of all. Rear defrost with A/C on is not a normal usage.
A 130A alternator cannot provide 130A continuously, 100A is about it.
Unfortunately, I do not have a clamp on AMP meter. Debating purchasing a cheap on to monitor amperage draw...
I always thought any voltage over 12V's should keep an engine running without flaw, but mine seems to die any time the battery voltage drops below 13V at the battery. I think the main power at the coil/ICM is less than main battery voltage. Mine typically measures ~0.1-0.5 less than main battery voltage.
Running the front defrost will require the AC clutch to engage. Sometimes during cold mornings I require front and rear defrost to be on. I agree though rear defrost isn't normally needed. I just turn it on to simulate heavy battery draw. I experience the same results with just the AC and headlights on (just takes longer).
Sorry, didn't mean to hi-jack the original thread...Seems like we might be battling a similar beast. :/
I always thought any voltage over 12V's should keep an engine running without flaw, but mine seems to die any time the battery voltage drops below 13V at the battery. I think the main power at the coil/ICM is less than main battery voltage. Mine typically measures ~0.1-0.5 less than main battery voltage.
Running the front defrost will require the AC clutch to engage. Sometimes during cold mornings I require front and rear defrost to be on. I agree though rear defrost isn't normally needed. I just turn it on to simulate heavy battery draw. I experience the same results with just the AC and headlights on (just takes longer).
Sorry, didn't mean to hi-jack the original thread...Seems like we might be battling a similar beast. :/
@michaelgt
Current draws with everything on: This is why a 3G alternator should have been standard equipment on all Fox body EFI cars.
Ignition system & computer = 12 amps
Fuel pump = 12 amps
Exterior lights = 15 amps
Fan (heater or A/C) = 15 amps (can run between 5-25 amps depending on setting)
Radio & instruments = 10 amps
Wipers = 10 amps
Rear window defroster = 5 amps (optional, not found on most southern fox mustangs unless the car moved down with the snowbird owner…)
That's grand total of 79 amps from a 65 amp alternator. Talk about overdrawn at the bank!
Full charge voltage for the battery is 14.2-14.5 volts with the engine running at 1200 RPM.
Full charge for the battery with the engine and all accessories turned off is 13.6-13.8 volts.
For more information see www.batteryuniversity.com/
Current draws with everything on: This is why a 3G alternator should have been standard equipment on all Fox body EFI cars.
Ignition system & computer = 12 amps
Fuel pump = 12 amps
Exterior lights = 15 amps
Fan (heater or A/C) = 15 amps (can run between 5-25 amps depending on setting)
Radio & instruments = 10 amps
Wipers = 10 amps
Rear window defroster = 5 amps (optional, not found on most southern fox mustangs unless the car moved down with the snowbird owner…)
That's grand total of 79 amps from a 65 amp alternator. Talk about overdrawn at the bank!
Full charge voltage for the battery is 14.2-14.5 volts with the engine running at 1200 RPM.
Full charge for the battery with the engine and all accessories turned off is 13.6-13.8 volts.
For more information see www.batteryuniversity.com/
Thanks for the info I checked mine and it's at 14.5 with the engine running at 1200 RPM. So I guess my battery and alternator are good?
Unfortunately not a good way to test. Local auto parts store can test them but you'll need to take them in
Blown88GT
Founding Member
DC clamp meters aren't cheap. AC clamp meters are.
You have to look at the voltage at the ECU & at the injectors. A momentary voltage drop may cause some of injectors not to open.
Blown88GT
Founding Member
maybe could have been but all I know that it's working now with the 19 injectors lol
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