Coleman G8C100 furnace tripping on high limit - http://www.hvacmechanic.com/ Forums
Original message
| trose
 |  "Coleman G8C100 furnace tripping on high limit"
, posted Wed 14 May 20:40  
Coleman G8C series furnace going out on high limit. Furnace was replaced 8 yrs. ago. Checked A/C coil and it was clean. Checked gas pressure and it was 3.5" W.C. Changed blower speed from MedLo to MedHi. Replaced high limit switch. Replaced pleated filter with fiberglass filter. Checked all returns to make sure they were clear and unobstructed. Cut in extra 12" X 6" hole in return drop to rule out possible blocked duct. When you start the system on a call for heat with the filter in the system will go out on high limit quickly. If you remove the filter the system will run without any problems. With the filter removed the SAT after the coil is a consistant 128 degrees. RAT is 72 degrees. Rated temp rise is 40 - 70 degrees. Any help would be appreciated!!
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Replies:
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| Houston204
| "Re(1):Coleman G8C100 furnace tripping on high" , posted Thu 15 May 01:01
A static pressure measurment across your furnace will help determine if the duct restriction is in the supply or return air. Most units list .5" W.C. across it. If it is 1 inch or more you have a severe duct restriction. (usually found in return air side)
"Tip of the Day" Remember to remove power first.
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