Gary Cole

Might first check the ambient air sensor. If it is out of range or indicates open with a multimeter the unit will default to heat. It is 2 wire thermocouple which plugs into the control board and snakes up past the evaporator. Not to be confused with the evaporator temp sensor. Don't recall at the moment what the ohm values should be vs temp. I took the values from my working unit some time ago when I had a similar failure.

I wasn't suggesting that our engines were not capable of full throttle operation. I routinely use full throttle when passing or climbing a short grade when I feel that more power would prevent a downshift. Transmission downshifts are not entirely free of wear and tear. Many years ago I was contemplating the purchase of a new truck with a Detroit 8V 92 engine. Detroit provided a spreadsheet which showed that the engine, when set at full rated horsepower, had a 40% shorter mean time between overhauls than when the engine was set at its lowest factory horsepower and rpm setting. In those days overhauls typically meant mean time between catastrophic failures such as broken crankshafts, dropped valves, piston separation, broken rods sticking through blocks, etc. Diesel engines have come a long way since then. I agree with Richard that a pyrometer is a good indicator of engine load and added one to my rv. I also use an engine oil temperature gauge as it indicates the real long term operating temp of the engine and whether it is tracking up or down.

There was an interesting topic on another forum discussing a new owners complaint that his ISL 400 Cummins lacked power when climbing steep grades. Not being a member I didn't comment. However, I was surprised at the number of people who recommended that he approach grades at full rpm with pedal to the metal and keep it that way during the entire climb. Perhaps gaining a minute or two in the process. Not to mention consuming fuel like he had a hole in his tank. My comment would have been that making a habit of operating a diesel engine in that manner would be the best diagnostic tool available if one was intent on eventually discovering a hidden, potentially catastrophic, weakness in an engine or transmission. A flaw which otherwise might have remained unknown for the life of the coach.

Considered Super Singles a few years ago. Spoke to a truck driver and he said that it was nearly impossible in the event of a blowout to slow down quickly enough to avoid damage to a very expensive wheel. He drove for a tanker company which used super singles on their rigs because they did less damage to gas station asphalt.