[Richard]

Its a good question. On my 95, there was a booster pump in addition to the engine pump. It kept the coach toasty while driving. The 99’did not have the booster pump, and would not keep the AH system warm enough to keep the interior comfy. Using the engine preheat switch helped a good bit to keep it comfy. But in really cold weathe travel, I turned on the diesel burner.