Deegee

iTrader: (1)

All,

I've been troubleshooting my AC problems in a 92 400 and I think I've narrowed it down to an electrical problem somewhere in the car, I'm hoping some of you can give me some advice on where to look next.

My AC compressor will not turn on unless I'm running direct power from the compressor to the battery.

The problem with this is that after a few days hooked up my battery dies completely and I need to recharge.

I thought by wiring it directly to a fuse (AC/defroster relay) in the engine bay would solve this problem but after a few days the battery is dead and needs another recharge.

Here's a bit of extra info, when I have it hooked up to the battery/fuse it appears that the AC lines are freezing even though the AC is turned OFF in the cabin. I'm guessing this is because the A/C compressor is always on but not blowing? When I have the AC blowing the lines don't freeze.

I'm guessing there is some sort of electrical issue between the AC switch in the cabin and the actual compressor itself but I have the slightest clue on where to look first. Any help would be appreciated.

jharris400

By bypassing everything and wiring 12v directly to the a/c compressor coil you have essentially made the compressor always on, that's not how a correctly functioning system is supposed to run. The compressor should cycle off and on as the refrigerant pressure increases and decreases, that's what your high and low a/c pressure switches are for. Your battery is dying because the a/c clutch coil is always energized I'm surprised it hasn't melted at this point they do get hot in use.

I suspect your low pressure switch is bad, the compressor clutch will not turn on if the computer thinks the pressure is too low in the system. You can test this by bypassing the low pressure switch, if the compressor turns on after reconnecting the compressor coil like it should be then you know either your system is low or refrigerant or the low pressure switch is bad.

Deegee

iTrader: (1)

Thanks for the reply, I had my mechanic recharge the system so I'm certain it's full. How can I bypass the low pressure switch and where is the low pressure switch located exactly?

jdmek998

Direct wiring it might also cause more stress on the clutch itself. Pressure switch is on the passenger side towards the firewall. You can run a wire and connect the switch itself direct. If you jump the pressure switch and it does nothing then its not your pressure switch. I had a similar problem where I could not get the Compressor to engage besides directly. Ended up being the ecm. Bought a reman from Tanin and its all good now. I tested resistance everywhere, swapped ac control unit and nothing worked. So it just might the ecm. Ecm sends the signal to the ac unit then to relay to ac comp.

Deegee

iTrader: (1)

Hmmm I've had my ECM serviced in the last year or two from Tanin, I'm hoping it can't be this. I'll see if I can trouble shoot the switch itself and go from there.

Thank you.