When the outside temperature gets pretty hot (low to mid 90s), I notice the AC clutch cycles periodically. There are noticeable time frames when it is not cooling a hot car, and this is because the clutch engagement has stopped. This is not a problem in the morning. The mornings are in the 70s, and the clutch stays engaged and the car cools down.

I’ve noticed that when the clutch first engages, it’s a bit rough, causing the engine to shake briefly, but it runs smoothly afterward. The AC was recharged with refrigerant in the spring, and I recently let a small amount out to check for overfilling, but the cycling persists.

I am thinking of routing a switch between battery voltage and the clutch to manually keep the AC clutch engaged. Is there a better way?

 

Do the two fans on the radiator shut off when the compressor clutch disenages?

I'm not a big fan of moditying wiring as the a/c system has safety checks that prevent damage to the compressor. The ECU commands the compressor relay to send power to the red wire on the compressor clutch. I'd probably back-probe the red red wire at the compressor and use a volt meter to see if the compressor is getting power when clutch isn't engaged. Work backwards to the relay if power is missing, or replace the compressor clutch.

I'd also check the high and low pressures with a manifold to see how the system is performing as well.

 

I drove home, and it was about 85°F, and the AC worked properly (no cycling of the clutch). The pressures with the manifold were on the high side, 350/50psi. Perhaps at the higher 90s temps, the pressure sensor was at the threshold pressure, resulting in that erratic cycling from random fluctuations being around that threshold pressure.