The A/C Clutch will not engage. What could the problem be?
A: There are several different
reasons why the A/C compressor clutch does not engage when you turn the A/C
system on. Typically, the most common problems are:
1- Low refrigerant prevents the cycling switch from engaging
the compressor. That's because it's acting as a safety for the
compressor. This can be tested by jumping the switch. Also check system
pressures. Low refrigerant pressures would indicate the charge is low and
the system will have to be
recharged to fix
2- Clutch coils can also
fail. The coil is what creates the magnetic field to 'pull' the clutch hub
into the pulley, engaging the clutch. The coil can be tested using an Ohm
meter to assure continuity.
3- Air Gap; That's the distance
between the front hub and the pulley. Typically, it should be about .025"
or about the thickness of a business card. When the air gap is too wide,
the magnetic field is not strong enough to pull the hub in. The clutch air
gap can be adjusted (usually on the vehicle). Also see 'clutch slipping'
4- Not enough voltage; the clutch
requires a full 12 volts in order to create the required magnetic field.
When contacts and connections are corroded, there may be a drop in voltage.
Check voltage at the clutch to assure proper voltage is present.
Note that these are the most
common reasons why the A/C compressor clutch does not engage. Other electrical
problems (ie.: control head, relays, etc.) will require
a wiring diagram for diagnosis.