spectra.. u say "Net result is that AC compressor works and trips the same way as on cold (blue) poition"....i dont think so. since the cabin air is getting heated by the use of the heater, its temp is rising. the same air is sucked in by the blower and passed over the evaporator coil. now this air is hotter than it should have been, because ac is on and it is supposed to lower the air temp with every passing minute and then trips when a preset temp is reached. in ur scenario, the air is getting colder becaquse of ac and then again being heated by heater, with a net increase in temperature. so how come the compressor will trip normally? it will continue to operate and strive to bring the temp down to its tripping limit (which it will not be able to attain due to the heater)
