A/c compressor on motor does not engage when dash a/c button pushed.

This could so many differant things causeing this i will try to give it to you in a nut shell .It could be an under charge or an over charge witch is not likely . But the first thing to do is have the R134 -a gas pressure tested it needs to be with in limits . Dose the heat work and the fan and the vent controls to send heat to differant vent areas to control there functions . If all of this is good then check the relay to see if voltage is going to the 3 switches . # 1 is the clutch switch for the compresser is it hot # 2 is the low pressure on the rear of the accumilateris it hot # 3 is the high pressure switch on the rear of the compresser is it hot . Look around all connectoins and fittings there is a green die in the gas with oil to suspened it if you can see green around connections you have a leak .If not the switches do go bad from time to time . Good luck

Check to make sure high pressure switch in back of compressor is plugged up . also make sure low pressure switch on accumulator has good connection.