Trailblazer EXT 04 - AC is not working

I am having a problem with my TB 04 AC. When I start the engine the AC is working like a fan/heater but when I the start to run my truck that is the only time it gets cool.
Can you pls give me a opinion on how to fix this problem.

Thanking you in advance.

Welcome to AF, the low side and high side pressures should be checked by a pro.

I have replaced the automatic clutch fan, now my AC is working fine.

What was wrong with the oe fan, the only effect this could have on the ac is if at low speeds the fan was not turning fast enough causing the pressures to rise in the condenser/high side, shutting the system down.