Just ordered and recieved a "rebuilt" compressor for my 300E, 1990. Calls for a 10PA17C. As I look at it I notice that there is not a "speed sensor" on the rear of the compressor as there is on the original. I have not started the replacement yet. Question is this: Is the speed sensor required? can it be taken off the old compressor and installed on the rebuilt one. I would hate to start the job and have to stop if this unit is not compatable.

The speed sensor is required, unless you wish to also rewire parts of the a/c system. If the new compressor is setup to handle the speed sensor, then you should be able to transfer it over. The shop manual has instructions on how to do so.

However, any decent compressor will come with a speed sensor already installed, leak tested, and verified working. I would recommend you return this one and get the correct part. Swapping the sensor onto it will probably void whatever warranty you received...

- JimY

1990 300E CLUTCH

Could you suggest how to test if clutch is bad? Mine is not engaging even if I short the pressure switch.

This is kind of "down and dirty". What I did to test the clutch was, locate the two wires that come up from the compressor through the intake manifold. Then, using a nail or sharp instrument, puncture the insulation to contact the wire. Run a wire from the battery to the nail and the clutch should engage. I don't remember which wire it was (I'm thinking yellow, but I could be wrong), Try both. If it does not engage or engages very weakly, then it is bad. It should engage with authority!

If by jumpering the pressure switch, the clutch do not engage. Does it confirm the clutch is bad or there is another input to clutch which may be causing the clutch not to engage?