We have a 2000 Coleman Cheyenne pop up with a Coleman mach roof unit. We turned it on today at home and the fan blows but the heater doesn't heat up and the air conditioner doesn't cool. Someone said if it's getting even slightly less than 110 v it might do that. We have the camper plugged into a 50 ft 3 grounded extension cord.

The distance of the cord is a big deal, 10AWG Cord would be best for this situation. If you have a 50ft cord, make sure that the cord is not wound up on top itself as this can cause a drop in voltage and a spike in amperage. Is the compressor trying to come on at all? If not, then you may have a problem with the selector switch or the thermostat. If the compressor is humming for a few seconds and then stopping and then trying to come on again, it could be a problem with voltage loss. Anything below 98.5 plus or minus 10% is too low the for the compressor to kick on.