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A/C causing big voltage drop

R

Renegade XJ

NAXJA Forum User
Location
corona ca
1989 XJ 4.0L Renix/AW4. Im not sure what the issue could be, my voltage reads 14 at all times but as soon as I turn on the A/C it drops all they way down to just above 9. I just added (yesterday) a 4 AWG ground strap from the firewall to the head and an other from the dipstick/block location to the frame in order to cure some odd idle issues but in the process I had hoped that my charging system would have inproved also. It has a brand new 100amp alternator from Autozone, I took it out and had it tested in two different stores and both said its fine. So any other thoughts? Do I just have a bad gauge?
 
Could be the blower motor resister going bad. Put the selector on vent & turn the blower to high & see what happens.

JIM.
 
I would verify the actual voltage at the battery with a meter when the AC is on. It could be that your gauge is inaccurate.

I improved my instrument panel ground on 3 of my Jeeps and that seemed to help, too.
If you look up under the dash on the driver's side bottom of the dash there is a black wire held on to or near a diagonal tubular brace with a self tapping screw. I took it off, extended it, and attached it to a 8mm shiny stud and nut on the left kick panel near the fuse box.
 
ILLXJ said:
Could be the blower motor resister going bad. Put the selector on vent & turn the blower to high & see what happens.

JIM.
Click to expand...
If the blower motor resistor was going bad, it would mean less current draw.
 
old_man said:
If the blower motor resistor was going bad, it would mean less current draw.
Click to expand...

You are right. I should have said switch. I'd been at work to long.

JIM.
 
Seconding Cruiser54, the very first thing you should do is check the real voltage at the battery, because gauge drop when you run the blower is common for this vintage XJ.

Make sure the belt is good and tight too. Not all XJ's squeal when the belt slips. My 87 would drop the power steering silently when the belt wasn't tight enough.
 
Try just the blower with the heater on. If the voltage drops, then its the blower motor.
Try the AC again, if it only occurs when AC is on, I would guess the AC clutch may be bad. The FSM may have a better diagnotic test for either item.
 
SleeperXJ said:
Try just the blower with the heater on. If the voltage drops, then its the blower motor.
Try the AC again, if it only occurs when AC is on, I would guess the AC clutch may be bad. The FSM may have a better diagnotic test for either item.
Click to expand...

Or, it's neither component that's faulty but just fairly normal for the gauge to drop like that. I've seen this on numerous XJs.

Check the voltage at the battery and compare that reading to the dash gauge.
 
Renegade XJ said:
1989 XJ 4.0L Renix/AW4. Im not sure what the issue could be, my voltage reads 14 at all times but as soon as I turn on the A/C it drops all they way down to just above 9. I just added (yesterday) a 4 AWG ground strap from the firewall to the head and an other from the dipstick/block location to the frame in order to cure some odd idle issues but in the process I had hoped that my charging system would have inproved also. It has a brand new 100amp alternator from Autozone, I took it out and had it tested in two different stores and both said its fine. So any other thoughts? Do I just have a bad gauge?
Click to expand...

Interesting. I just replaced my alternator with the same Autozone alternator when the bearings came apart in the original one and my voltmeter does the same thing.
 
My '89 Limited 4.0 does the same thing,even after upgrading all the grounds and battery cables. Everything still functions normally.

Must be an early Renix foible.
 
My '89 Limited 4.0 does the same thing even after upgrading the grounds and battery cables.

It's the fan.

Must be a Renix foible.
 
My 90 is doing the same thing, verified with a voltmeter. I think its my red top giving up the ghost at 10 years old.

Going with an interstate tomorrow
 
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