2007 Freightliner columbia

That’s a tough one. Usually it’s the other way around. Maybe the pressure switch isn’t turning the compressor off. Fan switch is obviously working, at an idle, and fan isn’t really needed while rolling. Condenser should be getting plenty of air while rolling. You could try watching the compressor at an idle. See if it’s cycling on and off. It should be. Fan should also be cycling on and off, opposite of the compressor. Fan on, compressor off. Fan off, compressor on. If compressors staying on, Could try kicking up the idle to 1500, see if they both cycle on and off. Compressor might be running constantly, and at a high pressure, isn’t cooling. Might be the pressure switch. Maybe when the compressor’s running all the time, at idle it’s not a problem, at high RPMs pressure gets too high. Just a guess. From what you’re saying, sounds like the condenser and radiator are clear, since fan is pulling air in at idle. And condenser is in front of radiator. Should be getting cooled well, when rolling. As hot as it is now, though, too much pressure, from a bad switch, or an over charge, might just be the problem.

 

Stops blowing air or air is not cool?

 

Need to know what the A/C pressures are.
Second thought is something could be going on air flow from the outside to the cab. Hot air is coming from the outside, forced air while driving. It comes straight into the cab.
Run a jumper wire from the compressor + to a test light in the cab. Does the compressor still have power while you are on the road?

 

I’d put a pressure switch on it. Worst case, you’ll have a spare for future diagnosis. I wonder if it starts blowing hot idling at 1500-1600? Trying to simulate Driving. It can be low on Freon and run all the time. Usually keeps blowing cold,Idling or driving. though not as cold as it could be, especially if it’s real hot outside. Like BoxCarkidd said, really need to know the pressure. Without a set of gauges, you’ll never know the high side pressure. So far nothing’s blown, that’s good. Even a cheap low side guage, that comes on the little hose kits. Screws on the can of Freon. That will tell you the low side pressure. Anything between 35lbs. and 55lbs. is close. The hotter outside, and especially the higher humidity will make for the higher psi. Up to 55 on mine. If it has enough Freon, and is higher than that. You probably need a pressure switch. I would just put a new one on. Then worry about Freon level. Once it starts cycling, if it’s still not right. It’s worth it, the switches go bad often enough anyway, Very easy to change. Won’t lose any Freon.