Hi I have been working on an x5 a/c gas pressures are ok compressor has been replaced pressure switch replaced but compressor won't kick in unless One of the pressure switch wires is earthed

ac units do not play up unless there is a gas leak so check wiring , fuses, relays or compressor operation before trying to add gas
If there is excessive gas in the system then the high pressure switch will stop the compressor
check wires and reverse switch for the light problem
check fuse for mirror problems

ac compressors are controlled by relays , switches , high and low pressure switches and fuses
replacing the ac compressor will require the gas charge to be administered as too little or too much will affect the high/low pressure switches
have it inspected by an accredited ac specialist shop for a proper diagnosis and a quote

there are 3 switches that control the operation of the ac compressor . There is a high pressure switch that will not allow operation if the head pressure goes too high ( excessive gas-blocked system-tx valve condenser fan not working )There is a low pressure switch that stops the compressor when the gas has leaked out and is insufficient A thermostat that will not register and so will not switch on the compressor and finally ac compressors will not work unless both the ac switch and the blower are switched on. Have the system checked out by an accredited ac specialists.;l

the high pressure switch kicks the compressor off when the pressure rises, the low pressure switch kicks it on, check that switch, unplug the wire and use a continuity meter to see if the switch functions, also check for power getting to the plug itself

It is probably low on freon. The low pressure switch will turn it off to protect the compressor because it needs the freon to circulate the oil. Hot-wiring it defeats the purpose of the low pressure switch and runs the compressor without oil. If you have not already destroyed your compressor by hot-wiring it, you can probably get it working better by charging the system.

You are bypassing the safety mechanism built in to prevent compressor damage. You either have one of two conditions, You truly have a low pressure condition(menaing you need an evac and recharge(fill the system with r134a gas) or a bad pressure switch. The switches are inexpensive replacing it will cost less than the charge to diagnose it, as such i would have it evacuated change the switch then have it recharged and a UV die added in so any other potential leaks can be found

You may have freon in system but compressor won't engage unless it's full under pressure. By jumping the the relay you're doing damage to compressor by running on low pressure. Have system evacuated and recharged to proper amount of freon - usually 4 lbs of freon

Hi:
There is a pressure switch on the side of the AC refridgerant reservoir area. If the switch is bad, or the level of refridgerant drops, the pressure switch doesn't allow the compressor to kick in. When you are running the wire from the relay to the compressor, you are bypassing the pressure switch. I am guessing that to fix your problem, you need to check the charge on the AC system, or check the pressure switch, and hopefully you will find your problem.!

The first thing to check is if there is enough gas. The compressor will not work when the gas is low. There is a small inspection glass on the line. This needs to be clear. If you see streaks or bubbles means the gas is low. Never mind the pressure or wiring for now, Add one can of gas and this should get that first part done.

the compressor doesn't have to be working for the gas to go in
you connect the gas to the inlet line and as the gas pressure in the system rises , the ac compressor will cut in normally and suck in the rest until the pressures are correct
of course you have to be putting in the correct gas because the switches are different