Nothing in the AC system is accessible from under the coach. The outside (intake side) of the condenser coils is accessible through the two large ducts on the side of the the coach in front of the utility bay and the outside of the evaporator coils is accessible through the access door in the basement were the filter is located.
The first step in troubleshooting a low cooling complaint on the basement AC is to check the amperage draw on the compressors. You can do this by watching the coach monitor panel that is located above the dinette on most coaches. First turn off the AC and wait 5 minutes, then turn the AC on with the thermostat set at least 10 degrees below interior temperature. Watch the monitor to see how many amps the first compressor draws when it comes on, which is usually a minute or so after the fan starts. A few minutes later the second compressor will turn on which will be indicated by a change in fan speed. Watch the monitor on the other power leg (if the first compressor was on leg one the other one will be on leg two) for the amp draw on the second compressor.
If both compressors are drawing in the 13 to 16 amp range (depending on the heat load), and they are drawing the same amperage, the system is operating to spec. and no repairs are indicated, but if one compressor is drawing considerably less amperage, you have a refrigerant (R 22) leak that needs to be repaired, If one of the compressors draws no amperage, you have a control board problem or a bad compressor.
SCS Frigette (the manufacturer of the unit) declared bankruptcy and went out of business the first of this year. Before they closed down, they were an excellent source for troubleshooting help, parts, and repairs on the unit. Now it looks like we will have to get the units repaired by a residential AC repair tech after the unit has been removed unless you have a control board problem, and that would have to be repaired by an electronics tech.
Gerald