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kidcross0681 · Nov 6, 2009, 04:52 AM

I have a bryant 80,000 BTU 90 plus two stage furnace Converted to propane. The problem is when it is in the low heat cycle the roll out switch trips. But on high it does not. I currently have the furnace in the emergency run mode. I have already cleaned the combustion air and exhaust vents. The burners seem to have a white flame on low. I was thinking it was a gas valve pressure problem but I cannot find gas pressure spec for the low stage anywhere. If you could find the spec or have any other ideas what it may be I would appreciate it thanks. John

hvac1000 · Nov 6, 2009, 04:56 AM

Exact model number

KC13 · Nov 6, 2009, 09:59 AM

If a proper propane conversion was performed, there should be a label placed over the natural gas values on the rating sticker.

kidcross0681 · Nov 11, 2009, 05:12 PM

Found the correct gas pressure and adjusted it but roll out switch still trips. Model number 355mav042080.

KC13 · Nov 11, 2009, 05:22 PM

This suggests a problem with the heat exchanger. I would suspect restriction of the secondary H/X or the cold-spot baffle. Your version of the circuit board may have a DIP switch to lock the unit into high-fire mode until it can be checked by a pro. Look at the schematic label for list of "SW - * - *" selections.