Carrier Gas Furnace Problem

mjm0073

i have a customer that has a 4 year old 90 plus high efficient two stage with variable speed blower . the klixon switch on the sealed combustion box trips at all different times . i have noticied the top of the furnace get real hot when its in low speed only , the flames are disturbed also in low heat only and only at times. i have checked gas pressure , intake and exhaust pipes , burner alignment , condensate drains. i am looking for ideas on where to turn next


thanks
mike

#CARRIERMAN

Hi mjm0073

Give me the magnahelic pressures for the collector and the burner box. It sound like you have a restricted secondary heat exchanger. Please tell me its not running on LP also. Let me know and I can walk you through the cleaning procedures.

Good luck
Rusty

__________________
Character is doing the right thing even when no one is looking. Intelligence is understanding and practicing the meaning of character.

mjm0073

rusty


i took the differential with a magnahelic guage from burner box to collector box and the readings i got were 2.5 inches of water column on high and .95 to 1.0 on low heat. i hooked up my manometer at sat and watched this furnace for about 45 minutes and i caught the gas valve not closing the high heat valve when there was a call for low heat right away . it only happened the one time but i think i caught the problem i installed the new valve and i am going to wait and see. i appreciate the help i will let you what happens in a couple days.



thanks again
mike

mjm0073

Rusty


By the way the system was running on natural gas.


Thanks Again
MIKE

#CARRIERMAN

Hi mjm0073

The pressures look pretty good. It looks like though the heat exchanger will probably need a good cleaning in a year or two. When the 90 plus Carriers get to 1.89" of water column the pressure switch will start to shuttle on high fire. Just something to look for in the furture.

Good luck
Rusty

__________________
Character is doing the right thing even when no one is looking. Intelligence is understanding and practicing the meaning of character.