I have a 98f150 4x4 with a 5.4 and here is the problem,when i turn the switch on for my heater to defrost or floor or anything related to the heater operation ,my ac compressor starts clicking on then off , making my rpms go up and down ,does this mean i have a bad switch at the panel or something else ,thanks

 

first off, the compressor is supposed to be cycling on the defrost settings.....

however, if it "short cycles", then that is a sign of a bad low psi switch on the a/c suction line.

as for the rpm jumping, when the compressor cycles in and out, the idle air control valve should be able to compensate for that. you might try taking it off and wither cleaning it, or replacing it as well.

 

yes i have replaced iac and it still does it,where is this psi switch located at is that the selector switch on the dashboard thanks

 

No, it's a sign the switch is working correctly but there isn't enough refrigerant in the system.

By Ford's design, the compressor is enabled in all HVAC function selections except OFF, FLOOR, and VENT. Consult your owner's manual.

Steve

 

x2, have the refrigerant level checked.