Civic DX Coupe L4-1590cc 1.6L SOHC MFI (1999)
Refrigerant Pressure Sensor / Switch: Description and Operation
Battery voltage is supplied through fuse 56 to the A/C compressor clutch relay contacts at all times.
With the ignition switch in ON (II), voltage is applied to the coil of the A/C compressor clutch relay through fuse 17. When you push the A/C switch ON
, and the heater fan switch is in position 1, 2, 3, or 4, a "ground" input is provided to the engine control module (ECM) or powertrain control module
(PCM) through the A/C thermostat and the A/C pressure switch.
The A/C compressor clutch relay is grounded by the engine control module (ECM) or Powertrain Control Module (PCM). When energized, the A/C
compressor clutch relay allows battery voltage to turn on the A/C compressor clutch.
The A/C ON indicator light comes on when the A/C system is requested.
A/C Pressure Switch
The A/C pressure switch is located in the condenser outlet line where refrigerant is in a high temperature/high pressure liquid state. The switch will sense
abnormally high or low pressure, and open the circuit. This removes ground, and the compressor will stop running.
