Drop In Voltage from Windows and AC on

[mmcgowan70]

I need some help figuring this out if anyone has suggestions.

I took out my dash to fresher it up, replace the radio and dash speakers. During the reinstall I noticed when It was running, with the AC on, the windows would work intermittently. Either they all will go up and not down or just the driver front and rear would work or some times none of them would go up or down. It only affects the passenger side windows.

There is a drop in voltage when I press the switched on the drivers door. Down to almost 8 according to the gauge in the dash.

It did not do it before so I know I have knocked something loose just not sure where to look exactly. Radio is also not in.

The ground behind the dash looks clean and the wires were secured on it.

I just have no idea what to do from here.

 

[mmcgowan70]

1988 Suburban 454 TBI 2WD

 

[slammed84]

If it were me, I would be running the power windows through some relays. They would probably work much better, and put less strain on the electrical system in the long run. Sounds like worn out motors/ tracks/regulators are stacking up and pulling a lot of current when you try to operate them. A relay (triggered by your window switch) will allow full battery power to the motors and bypass the factory switch wiring.

 

[mmcgowan70]

I’ll look into the relays. It’s something that kept popping up on my searches

 

[75gmck25]

I had similar symptoms when my alternator was going bad. With lights and blower on it would drop down to about nine volts at idle, but went to about 12-13 volts when I turned them off. Swapped in a rebuilt 12si 94 amp alternator and it fixed the problem.

 

[Matt69olds]

First things first. Remove and clean the battery terminals. Check the grounds at the engine, body, and firewall. Make sure the alternator belt is tight. Find someone with a charging system tester, make sure the alternator is actually capable of supplying the required current. Most vehicles with A/C and power windows will have at least a 78 amp alternator, maybe someone over the years has replaced it with a lesser alternator

Before making a bunch of changes to the truck, verify system voltage. If the voltage really does drop that much, then it’s time to start looking at the charging system and wiring. If the gauge reads 8 volts, but the system voltage isn’t dropping that much, then I’d start looking at the instrument panel.

If the system voltage drops with the blower motor on high, check the connections at the blower relay. You may find wiring and connector bodies starting to melt.

 

[fast 99]

Above post matt69 first

Although I agree using a relay may at least temporarily solve the issue it is really crutching an underlying problem. Even when new at idle AC on voltage dropped. Windows should work on battery voltage alone. Without engine running.