A truck without AC in July is a safety problem, not a comfort problem. Mobile mechanics diagnose and repair cab and sleeper cooling on site.
The mechanic checks the system end to end — compressor and clutch, condenser, blower, pressures, and leaks — and carries the common failure parts. Many AC calls are electrical (relays, switches, blower motors) or a failed clutch rather than a lost refrigerant charge, and those are straight roadside fixes.
Electrical faults, clutches, blowers, and many component swaps are handled on site. A full evacuate-and-recharge or a buried evaporator job may point to a shop — the mechanic will tell you which side your problem is on after diagnosis, before you commit to anything.
RIG works on anything diesel — and only diesel. Big rigs and semi trucks, diesel RVs and motorhomes, diesel pickups and work trucks: every mechanic in the network is a diesel mechanic, so your breakdown goes to someone who works on engines like yours every day.