AC doesn't cool at freeway speeds

[ChiefBob]

The electric fan on the condenser doesn’t run all the time. It cycles on and off so there is some switch or sensor somewhere. I agree that at highway speeds it shouldn’t need the electric fan.

[fourthgear]

Refrigerant charge maybe correct ,buts was the system evacuated & brought to a deep Vacuum to recharge system? Sometimes air/moisture can sneak in to the system when recharging & can cause strange issues.

A bad sensor can cause the Compressor Clutch to disengage, the Compressor Clutch engages & disengages as needed when driving & Pressure sensors control this .

Weak or bad Compressor clutch .

Outside air infiltration , bypassing damper doors or inoperative .

Extremely dirty Condenser Coil or lack of air flow across it .

Bad Compressor

The list can go on , but its hard to trouble shoot when its not in front of you.

[lwmcguir]

Originally Posted by ChiefBob

The electric fan on the condenser doesn’t run all the time. It cycles on and off so there is some switch or sensor somewhere. I agree that at highway speeds it shouldn’t need the electric fan.

My electric fan kicks on when you hit the AC button

I have no idea if it switches off going down the road

[HarryTh]

Maybe you could rig up a test light with a long wire so you can see it underway. Hook one side to ground and the other to the wire going to the compressor to see if it loses power at highway speeds. (Very low tech.)
Harry

[Bill Johnson]

Run the engine at 2600 rpm and see if the ac stops

[simidrm]

It almost sounds like it’s icing up, check the condensation drain port and make sure it’s not plugged, and if it has a drain hose make sure it’s pointed down with no kinks, if the hose is missing airflow at highway speeds could be letting the condensation back up around the evaporator and icing it up.