Name: Greg City: Girard Ohio
Question: I live in a 1981 Admiration 14 X 80 mobile home with the original Coleman Presidential Series Furnace. Model Number 7663. Natural gas fired. Furnace is not equipped with A/C. Home is located in Northeast Ohio. I have live here for 12 years. Last spring, when we were experiencing our last few 20 degree days, my blower in my furnace would kick off and then about two minutes later, kick back on. The burner stayed lit while this happened. Well I am familiar enough with the system to figure it was the limit switch for the blower. I called my furnace guy and he replaced the switch. It seemed to run fine after that. Well this winter, when the temperature dipped to around 20 it started the same thing again. To date, I have had five different switches put in by three different repairmen and it still kicks on and off. One theory is that the switch is doing its job and I have a lot of cold air getting into the system and its below the lower tolerance set in the switch. The switch is a 110 degree with a 30 degree differential. The factory calls for a 115 degree with a 20 degree differential. One of the repairmen suggested the higher differential switch would help and it did stop the blower from kicking on and off as often. When its 20 degrees outside it does reach the temperature set at the thermostat and shut down as it should. It becomes a major problem when the outside temperature drops below 10 degrees. It starts to lose degrees because it kicks on and off so often. Blower is always off for about two minutes then comes back on. The entire time the burner stays lit. I really can't believe the cold air theory. Shouldn't I be able to walk into a 55 degree house and turn up the thermostat to 70 degrees and the furnace run until it reaches the set temperature? If I remember correctly the furnace use to do just that. One of the repairmen said that it kicking off was designed into the switch. I can't believe that either. All the repairmen said that other than this problem the furnace is in good working order. Blower has been checked for RPMs and Amp draw. Both were within factory specs. When the blower was removed I had the opportunity to look down in around the firebox. Where the fan switch comes through the cabinet next to the firebox is there suppose to be a metal shield or shroud on the inside to deflect the air coming into the furnace from hitting the switch directly? There is none on mine but I thought maybe if there was suppose to be then this might be the reason for it behaving this way. Just one of my theories. One more observation, if I put my finger against the back of the fan switch while the blower is running you can feel the switch "pop" when it goes off and again when it goes back on. Any suggestions or theories would be appreciated. At this point I am seriously considering buying a new furnace. Of course I would rather not.
Name: jerry | Date: July 8, 2006, 14:57
Answer: MY GIRLFRIEND HAS THIS PROBLEM---HAVE YOU EVER THOUGHT THAT LOW LINE VOLTAGE IS CAUSING THE CURRENT TO RISE IN THE MOTOR THUS OVERHEATING IT AND KICKING OFF THE THERMAL SWITCH BUILT INTO THE MOTOR? IS YOUR MOTOR VENTS CLEAN OF LINT?