AC compressor cycling

[jeedee]

2002 Ranger, XLT, 3.0 L, Auto, 4-door. AC compressor keeps cycling every 3 or 4 seconds...on...off...on...off....etc., ONLY if compartment vent-selector switch is on....ANY position....(NOT the blower switch). If the switch is off....no cycling of compressor.....Sensor...? Relay...? Appreciate any input.
Thanx
Charlie.

 

[RonD]

AC compressor is turned on when AC is selected of course but also when Defrost is selected.

AC system has a high pressure switch and a low pressure switch on the coolant lines
If you are low on coolant(freon) then compressor will cycle on and off
If coolant line is plugged then high pressure switch will cause the on/off
Low on coolant is usual cause for cycling

In 2002 the PCM(engine computer) runs the AC system
Both pressure switches are connected in series to a GROUND and then to the PCM
Ground--------high-----------low----------PCM

In the engine fuse box is the AC clutch relay, when this relay closes the compressor clutch gets power and compressor is ON, spinning

When you select AC or Defrost on panel 12volts is sent to PCM, this is the AC Demand signal, but doesn't power anything
PCM then Passes the GROUND from the pressure switches to the AC clutch relay, which closes it and compressor comes on

If one of the pressure switches is opening(cuts Ground) the AC relay will open and compressor is off, when pressure switch closes again so does the relay and compressor comes on

Check pressure in the system

 

[jeedee]

Thanx very much, RonD, for the info. Will have the AC pressure checked.
Charlie