Forced Air Natural gas Heater keeps cycling on and on

Thank you for bearing with me in trying to assist you. It is diffucult to isolate some issue's quickly without being able to see the system personally. I did read your other comment a few minutes ago on the dirty coil. Back in the 60's we did some stupid installs due to less knowledge than we now have. To answer your question of cleaning the coil, the only way it can be properly cleaned is to remove it from the furnace and wash it with coil cleaner. Regardless of what you have been told it can be done. I do it all the time and granted most of the time it requires extra work cutting it out of the box and making a new cover when reinstalling it.

1. Stupid install: The evaporator coil should never be downstream, (after the heat exchanger). It should be on the return side of the unit.
2. I will need you to picture this in your mind as I explain it. Let's think air flow since that seems to be the issue here. Please bear with me here as I am trying to get a picture in my mind of your situitation. First: if I understand correctly, everything works properly with the blower compartment cover and (or) the air cleaner removed which both are on the return side of the system. So the flow of air is through the blower to the heat exchanger to the evaporator coil and into the supply ducts. I am going to use a water circuit to demostrate this, see pitcure below. A. with valves 1,2and 4 open, valve 3 closed we will get 60 psi water (full air flow) through valve 4. If we close valve 4 (Totally blocked evaporator) no water comes out, (no air flow). Again, open valve 4 we get full flow. B. If we close valve 1 half way we will get 30 psi through valve 2 and 4, (restricted return). C. Leaving valve 1 half closed, valve 2 and 4 open (30 psi). Now we fully open valve 3, (remove the air cleaner or blower compartment door) we once again get 60 psi through valve 2 and 4. I hope I am not losing you onthis but this is the reasons that it appears to be a return side restriction verses a supply side restriction unless I am not reading your comments properly.Also, I would like to know the size of your air conditioner as a 40x20 return is good for 7000 cfm which would be a 5 to 6 ton air conditioner.

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Posted 3 years ago by stanhvac1 in Heating

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