My volvo S70 compressor does not run and I have tested and eliminated all causes except the linear pressure switch (High Pressure switch)! It has the automaticc climate control system.

1. The compressor runs if I bypass the AC relay

2. The pressostat works fine (I tested it)(tested with ohmmeter as well as bypaassed to test)

3. The low side pressure is fine (Tested with AC pressure guage)

4. The AC switch sends +12V to the ECM via the pressostat (Tested!)

5. Tested the AC relay (Works fine)

6. The ECM is supposed to activate the relay under these conditions by grounding the low side of the relay. It does not ! (It is around 11.5 V)

7. The Linear pressure switch (actually sensor) is putting out only 0.11V, with or without the compressor being turned on. So I suspect it is not functional!

8. Does anybody know what voltage is expected out of the linear pressure sensor for the ECM to be happy and turn on the AC compressor? Is there a better way to test it other than spend a $100 and get a new sensor!

Any information from the AC experts would be appreciated. It is getting warmer here in NJ and soon it would be impossible to drive without AC!!

Thank You
Ramesh52