A/C Draw

Once again it's A/C season. I usually run my A/C about once a month in winter/cooler weather just to keep everything working. I've noticed that when I run it the gauge drops in charge quite a bit (as in down to 10-11). Is this a normal thing?

Also, even when I run the blower for the heat in winter it drops considerably (not so much, but noticeable). What kind of testing or diagnostic should I be doing if in fact this is not OK. It's a 90 so no OBD.

Electrics are NOT my strong suit, so if someone can run me through it like a first grader I would appreciate it

It sounds as if your battery is about to die. How old is it? It may be time for a replacement?

Fran

It's not normal for your electrical to ever drop down to ten or eleven volts.

First, get a good digital volt meter and check at the battery to insure your dash gauge is correct. You should measure 13.6 to 14 volts with engine running at idle.
If yes, turn on your lights and record the battery voltage. Then, with lights off, turn the A/C and record the battery voltage.

Turn the blower motor (vent or heater) and record the voltage. Then turn on the defroster and observe the voltage. Selecting defrost should engage the A/C, which should also turn on the electric radiator fan. The combination of the heater blower motor and the engine fan should put a heavy load on the alternator/battery system. Again, record the battery voltage. It should still be above 13.6 volts. If not, the alternator is not putting out correctly, or there's bad motor in the circuit, or a high resistance short to ground in one of the circuits you turned on.

Good advise there from xjbubba. I would feel OK with 13 volts at the battery with everything running, A/C, Blower on high, E-rad fan on, head lights on brake lights on...

XJ dash voltage gauges are notorious liars so trust the multi meter (Digital volt meter) readings at the battery, not the dash gauge, especially Renix years like yours, 87-90 years. The Renix years are also notorious for multiple ground wire problems that cause all sorts of headache problems like wandering idle speeds, and low volt meter readings. 5-90 noted in another thread a few days ago that the XJ volt meters also have a problem with a calibration magnet that can move and throw off the calibration as well.

My dash gauge (87 Renix) typically runs between 13 volts with just the motor on, to a point right at the beginning of the left side red line with the AC blower on high and the head lights on, but the battery itself is still at 13. 25 to 13.5 volts. Try turning on the ignition but do not start the motor, and read the battery voltage on the dash gauge, mine reads right at the begining of the left side red line with nothing running (Blower off, head lights off) just the ignition in the on possition.

Same here. My guage reads anywhere from 11-14 volts depending on what kind of mood its in. I noticed the other day that when I hit the ac it dropped to like 11 but the underhood readings were still bout 13.4.

I got out the DMM and checked the voltage at the battery. I think I'm going to stop worrying about this. I got 14.34 at the battery at cold idle with nothing turned on. Turned on the lights, A/C, Aux fan, one at a time. Never dropped below 14. Turned them all on at the same time it dropped briefly to about 12.8 when the A/C started it's cycle but came right back up.

So the gauge is lying just as y'all said.

Thanks