Speaking as an ex-designer/engineer of mobile A/C systems, every system designed for off road vehicles has additional restrictions put on it that other systems do not. Vehicle A/C system for over the road use have better airflow through condenser and less chance of clogging or getting dirty from operating environment. Evaporator sections are easier for over the road vehicles as well because even in using 100% fresh air in the cabin, the dusty, dirty , and downright awful environment seen by off road systems does not exist--or at least for very short duration(ie-dust storms, following a un-tarped trailer, etc). The A/C systems for most tractors are designed to maintain an air delivery into the cabin that at best will only drop the air temperature a maximum of 30-35 deg f. Note that is the incoming air temp to the evaporator-- not the ambient temp. Most systems are set up to have an option to use recirculated from the cabin to air in higher ambient and higher humidity environs. Most if not all off road systems are set up to have some fresh air introduction even in recirculate mode to keep the cabin pressurized and prevent infiltration of outside contaminants into the occupants/operators volume. For very severe environs an outside dust collection and filtration system may be required in addition to the regular A/C system filtration components. Religious attention to the cleaning and replacing of filters when needed is key to optimal operation of off road systems. Sometimes additional cleaning of evaporator system may be necessary if filtration fails or is compromised. Likewise for the condenser. Since most tractors are not moving at 20 mph or anywhere that fast when operating, the function of the engine fan, shroud and all inlet filter screens, baffles and seals in and around the condenser/radiator area are more important than ever. A single baffle or foam seal that is missing or removed and not replaced correctly can allow hot air from exhaust side of radiator to return in front of the condenser. Condensers are designed to operate effectively in at most a 120 deg ambient and engine radiator discharge air temp can reach 160 deg f quite easily. Plugging or blocking air passages in the condenser/radiator sections by grass seeds, chaff, or dirt can cause an otherwise satisfactory operating system to become in efficient. Remember, an A/C system just moves the heat from one volume to another--whatever heat is removed from the cabin area is dumped in the condenser to be removed by the air flowing across it.