Furnace Blower Cycles And Shuts Off Permaturely
I hope someone has an answer to this. The blower of the furnace turns off while the burners keep burning. After about 30 seconds, the burners shut off (I presume because of high temp limit, since there is no air blowing), then about 10 seconds after the burners shut off the blower turns ON again, then the burners kick in again and the blower runs for about 2-3 minutes but then it shuts off again while the burners burn, and so on repeteadly. All this while the therm. is calling for heat. It is as if the blower cannot run constantly while the burners are burning. Fan is set to Auto on the therm. Some more info. When the unit is first turned ON the fan appears to be able to run for a longer time while the burners are burning, but eventually shuts off before the burners go out. As the system runs cycling like this, the blower cycles get shorter, that is the blower cannot stay on for more than 2-3 minutes while the burners are burning. I realize this is very dangerous as the burners and the core will get very hot since there is no air flowing. The exhaust fan is running all the time while all this cycling is happening. I have called a heating specialist to come see the system but I want to make sure I am well educated so that he does not give me the run around.... Also, what should I expect to be charged in the north east for furnace maintanance service if no new parts are needed ? The system is a York 80 Diamond, natural gas, FHA. The york 80 comes with an electronic furnace controller White-Rodgers model 50A50-210 (I believe the 50A55 replaces the 50A50), so there is no hi/lo limit controls that I can adjust... I don't know the age of the furnace but the house is 20yrs old. Any help and advice is greatly appreciated.
Answer:
the Capasitor is to help start it but if the capasitor is weak or not working it will let the motor run hot and start cutting in and out as it get hot and them cools off to start again. Motor after starting will run hot and cut out with out the ade of the capasitor. It need the capasitor to run and start also. Most motor will start with out the capasitor but will not run for long and start cutting in and out. In this application it will not run very long with out the ade of the capasitor and start cutting in and out. I have seen blower motor turn free and still have bad bearing. It could have been worn a good bit and then you oil them up and it turns free but the bearings is letting a armoture come too close to the fields in the motor and cause it to heat up because of not dragging but the motor verses the field possion in the motor. Motor on direct drive have to be perfectly in the center of the windins or it will run hot and start cutting in and out. 5 or 6 thousanths of a inch out of center will or can start make it run hot and still turn free as can be. If the capsitor is weak or out the motor will act up running or starting in either case.