AC Compressor not engaging

[RogerDodger]

74 318 factory air. The compressor is not kicking in when the AC is turned on. I don't see any blown fuses. Worked last year. This was the first time I tried it this year. Not sure where to go after the fuse check. Wiring looks to be in place and good.

[b5blue]

Charge leaked? 

[Nacho-RT74]

Locate the dryer and jump out both terminals arriving to the presostatic switch. If engages, you are out of refrigerant or switch is damaged.

[AKcharger]

I found running g though stock harness I was only getting 10 volts, made a relay to send 12 volts direct to clutch, that worked.

[RogerDodger]

I found running g though stock harness I was only getting 10 volts, made a relay to send 12 volts direct to clutch, that worked.

I am getting 12 volts to the clutch when the power is not connected. When connected and running only getting 9v. When connected it clicks and sounds like it is engaging but not drawing down the motor as much as I am used to when properly functioning. It loses 3v when connected. The clutch will spin but doesn't appear to engage the compressor. Could the clutch be the cause?

[RogerDodger]

I have the clutch off and the compressor will still turn. Thinking I will replace the clutch first and try that considering the compressor runs $500.

[John_Kunkel]

In the pic below,the compressor pulley will turn any time the engine is running but the hub will turn only when the clutch is engaged...if you can hear the clutch click but the hub isn't turning at the same speed as the pulley, then the clutch is slipping. This might be due to wear or insufficient voltage to properly energize the clutch.

I would do as previously suggested, temporarily connect a wire directly from the battery to the clutch to see if it will stay engaged, if it will, then the car's wiring circuit isn't maintaining correct voltage under load.