I spent the last few days overhauling my system for 134. I replaced the reciever and compressor and flushed everything.
I tried charging from the low side, but made better progress from lo/hi side. What is technically correct? The compressor didnt fire until the fifth can, when I ran a 12 volt wire to the blue white lead.
The system worked like it should. The auxiliary cooling fan came on (in front of the radiator) and conditioned air came out of the vents.
So now I hand fire my compressor with a switch in the passenger compartment.
Is there a pressure switch in the system--why doesnt the compressor get its signal normally? If so, will I have to evacuate the sytem to install a new pressure switch?
Please remember 50% of the fun on these cars is solving the technical riddles.The other half is pulling up to the dealer to buy parts and watching people pick up thier cars at service.

"Please remember 50% of the fun on these cars is solving the technical riddles.The other half is pulling up to the dealer to buy parts and watching people pick up thier cars at service."

You can imagine my fun then... watching DIYers play with these simple systems (vbg LOL).

The pressure switch is on the drier and should have connected the circuit with a very small ammount of pressure. The original switch was probably just a low pressure switch (for preventing the compressor from burn-out pumping a dry system). The new switch will be a low/high pressure switch which will prevent damage from over-pressure; very necessary with R134a systems.

The system will have to be discharged to remove the switch. Check the circuit at the switch to be sure its the problem. If its the problem one side will be hot (battery voltage approx) and the other side not.


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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Folks,

Where can I get the different pressure switch to be used with R134, and what do I ask for.. As I recall, the switch currently installed has two leads for the fan and two for the compressor.

This would be for use with my aftermarket A/C on my 240D.

Thanks for any help,

PS. Steve, I'm sure that I speak for everyone when I say there is no need to apologize for a delayed response. We appreciated very much your sharing your vast knowledge with us. LB

Steve:
I knew I had it coming to me even as I typed those lines!
But truthfully, I have rebuilt five or six engines, including the 240D Diesel and a Rotary. In my beginning years, I also destroyed a lot of stuff.
Usually my work is very good. I shouldnt have been cocky, but you cant blame me for feeling a sense of pride watching the well-to-do pay their service bills.

On the installs where the trinary switch is needed, we are using a switch from a A/C hose rebuilder. It has a low pressure and a high pressure switch for the fan built into one. It has 3 functions.
1. Turn off the compressor if you have refrigerant loss
2. Turn off the compressor if you have and overpressure situation
3. Turn on the aux fan at over 225psi.

This will take out the old style temp regulation of the aux fan. In 134 systems, the pressure may build faster than the temp.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM