w201 m103 ac low pressure switch wiring - Page 2 - PeachParts Mercedes-Benz Forum

Mxfrank · #16 11-07-2018, 08:57 PM

Quote:

Originally Posted by lsmalley

Correct. I do have the dual function switch according to the packaging as well as the fsm. Contact has continuity with engine off. What I did notice was when I grounded one of the wires that goes to the pressure switch, the clutch engages. If I ground the other wire nothing happens.

I'll ask the question a different way, because I'm not sure what you're saying. If you remove both wires from the switch and connect them together directly, does the unit engage?

Also explain how you're measuring output from the sensor. I'm pretty sure it's hall effect, so you need to have a supply current. It's not the problem anyway, since the system engages when the pressure switch lead is grounded. Your problem is either low pressure, the pressure switch itself, or a bad head unit. Have you measured your system pressure?

lsmalley · #17 11-10-2018, 10:23 PM

Quote:

Originally Posted by Mxfrank

I'll ask the question a different way, because I'm not sure what you're saying. If you remove both wires from the switch and connect them together directly, does the unit engage?

Also explain how you're measuring output from the sensor. I'm pretty sure it's hall effect, so you need to have a supply current. It's not the problem anyway, since the system engages when the pressure switch lead is grounded. Your problem is either low pressure, the pressure switch itself, or a bad head unit. Have you measured your system pressure?

If I disconnect both wires and connect them together, nothing happens. If both wires are disconnected and I take one of the wires (let's call it wire 1) and I ground it, then the clutch engages. If I try that same thing with wire 2, nothing happens. So wire 1, whenever grounded, will engage the clutch. Wire 2 on the other hand has no effect if I ground it or not. The system pressure is about 35 psi low-side. High side is about 200 or so, when it reaches about 250 psi on the high-side the fan turns on until the high-side goes back down to about 200 psi then the fan shuts off. The way I've been using my a/c system is by running a wire from the compressor clutch to a fused toggle switch inside the cabin.

Diseasel300 · #18 11-11-2018, 12:42 AM

You just keep going in circles don't you. The wire you ground to engage the clutch is the one up to your MAS/Klima relay to call for cooling. The wire that does nothing is the one back up to the pushbutton unit. The fact you can ground the MAS/Klima wire and the clutch engages, but connecting the two wires together does nothing tells you exactly where the problem lies.

lsmalley · #19 03-27-2019, 11:10 AM

Problem ended up being the evaporator sensor. I checked every ac component and finally ended up checking the probe sensor and it was severed. I spliced it back together and a/c now functions normally.