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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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What is a High Aux and spill limit switch open. What are some

Customer Question

What is a High Aux and spill limit switch open. What are some suggestions to correct this problem on a Coleman furnace
Submitted: 6 years ago.
Category: HVAC
Expert:  BillyHvac replied 6 years ago.




is this a downfow unit?

Customer: replied 6 years ago.
No it's a upflow. The air is forced up.
Expert:  BillyHvac replied 6 years ago.


Aux limit and draft trip will be a reset button in the middle of a switch like this


Customer: replied 6 years ago.
Yeah I check those and all of them (3) were closed. It's getting the 24 volts all the way back to the board but the ignitor nor the gas valve are doing what they're suppose to be doing. Do you have any other suggestions on fixing this problem?
Expert:  BillyHvac replied 6 years ago.


Possible code fault...but it sounds more like a pressure switch fault. have you checked pressure switch power in and out when unit starts? And have you checked the priXXXXX XXXXXmit on the front wall behind the gas valve?

Customer: replied 6 years ago.
Pressure Switch? Are you talking about the switch which the tube comes from the induction fan motor? I have ohmed it out and blew in the tube. It was closed. I also checked the voltage going in and out of the priXXXXX XXXXXmit . I was getting voltage in and out. Could it be a filter problem being clogged?
Expert:  BillyHvac replied 6 years ago.


First go here....


check all safeties based on location. Make sure we hit all of them. Then we can go from there

Customer: replied 6 years ago.
can tell me how to check the pressure switch and the priXXXXX XXXXXmit switch?
Expert:  BillyHvac replied 6 years ago.


With meter///check for 24 in one side and then 24 out the other.


No meter......Remove 2 wires from limit and use a paper clip end to stink in the bottom of each wire and tape so no metal shows...really anyway to just get the metal wires to connect. This bypasses the limit (testing purposes only).


The pressure switch depends on if you 2 or 3 wires to it.


If 2 wires...remove wires and hold apart...start furnace....after exhaust fan kicks on touch the 2 wires together and hold them that way...see if fault clears.