Bypass a/c low pres. switch. - PeachParts Mercedes-Benz Forum

420benz · #1 06-07-2009, 09:33 PM

A/c clutch won't kick in. Need to add freon. How can i bypass the switch?

Matt L · #2 06-07-2009, 10:26 PM

If it's a two-wire switch, you can short the leads. Never short terminals if there are three wires (but I don't think yours does). You could also heat the can with some warm water to push some refrigerant into the system, which will close the switch. That is, if you now have some positive pressure. If not, you need to remove any air and water that got in.

420benz · #3 06-08-2009, 09:54 AM

Thanks Matt, i will give it a try.

big dog 2 · #4 06-09-2009, 10:24 AM

Is your system still R-12 or was it converted? Did the bypass work? I have the same problem and my terminal has 3 wires. Not sure if I want to play around with it............

420benz · #5 06-09-2009, 10:32 AM

Quote:

Originally Posted by big dog 2

Is your system still R-12 or was it converted? Did the bypass work? I have the same problem and my terminal has 3 wires. Not sure if I want to play around with it............

It is still R12. I did not try it yet. I will do it today.

Matt L · #6 06-09-2009, 10:35 AM

Quote:

Originally Posted by big dog 2

Is your system still R-12 or was it converted? Did the bypass work? I have the same problem and my terminal has 3 wires. Not sure if I want to play around with it............

What year is your car?

Three-wire sensors are usually transducers rather than switches, and shorting terminals can burn things out.

david s poole · #7 06-09-2009, 10:44 AM

guys within 30sec of connecting gauges and r12[either can or bottle] the low press switch will have closed and the system will run.don't mess with wires there is no need.

Matt L · #8 06-09-2009, 10:46 AM

Quote:

Originally Posted by david s poole

guys within 30sec of connecting gauges and r12[either can or bottle] the low press switch will have closed and the system will run.don't mess with wires there is no need.

Even faster if you let some into the high side. Just be sure to close that valve before starting the compressor.

big dog 2 · #9 06-10-2009, 09:58 AM

Thanks for the information! I didn't think the switch would close just by hooking up the gauges. My system is completely empty which worries me about a leak. Last charge lasted about 3 years done by the dealer.

Matt L · #10 06-10-2009, 10:38 AM

If it is completely empty (no pressure), you should evacuate the system to remove air and water. A new dryer would be a good idea as well.

big dog 2 · #11 06-17-2009, 02:29 PM

Thank you david s poole!

The clutch engaged almost immediately after hooking up the 134a refridgerant (system was converted to a 134a three years ago). No need to mess around trying to bypass the low pressure switch! With my luck, I would have shorted out something and really had a problem! System works fine for now..........

#12 06-17-2009, 03:10 PM

The low pressure switch should never be jumpered. The only exception would be in a system troubleshooting process to see if the clutch is okay or the switch itself is bad. In this case it should be done very quickly, just long enough to make your check.

Jumping should never be necessary in the normal system charging process.

gmercoleza · #13 06-17-2009, 08:46 PM

Larry are you back? Gearing up for the alternative refrigerant conversion wars?