Mercedes: Mercedes A/C, mercedes benz 190d, r134a refrigerants

Question
I have a 1987 MB 190DT and had the system changed to 134a with rebuilt compressor, receiver/dryer and expansion valve.  Now system doesn't have power to compressor clutch. What pins on A/C relay can be checked to see if that relay is good?  What else should be checked?  

Answer
Answer:

#1. A/C Pressure Switch = jumper the connector to see if your compressor runs.
#2. A/C Speed Sensor on the compressor.


Climate Control:
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PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 190D 2.5 Turbo
Part: A/C Pressure Switch
 Note:  
2 bar low pressure and 30 bar high pressure binary switch. This switch is designed to be compatible with R-12 and R134a refrigerants. Located on reciever-drier with 2 spade terminals. Used for compressor cut-out.     
R1054-178181 A/C Pressure Switch ACM IN STOCK $27.08  
 
R1054-178181 A/C Pressure Switch IN STOCK $22.21  
  
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