Belt wear

CHECK THE HEAT EXCHANGER BUNDLE

We have 24 of the Carrier gas-fired package units on the roof of the school. After 8-10 winters and countless heat cycles the weld-seams of the heat exchanger tubes will rust and split open, causing the flame to start to rollout and the rollout switch to disable the burner. The blower fan will continue to operate blowing cold air, and the thermostat will continue to call for heat, but the draft fan will lock out so no heat. The safety gas valve they found closed may be programmed to close when the rollout switch trips as a precaution. There should be an LED "flash code" you can use to confirm why it tripped out. Or fire up the unit with the side panel off and watch the burners--if the exchanger is cracked the flame will dance in an unstable way and "roll out" will be pretty obvious. If your unit is 10 years old and it has never been changed it is likely due. If you don't see any actual roll out and the flame looks good, the rollout switch itself could be bad--cheap part and super-simple to replace.

Changing the exchanger bundle out is about a 2-hour job for two competent guys--we do them regularly, so we have gotten pretty fast. The size varies depending on the size of your unit--the larger ones can be cumbersome for 1 guy to handle. Our units are 2001 models and are generally very reliable and pretty simple. If something goes wrong in the wintertime with them, 80% of the time it is the heat exchanger reaching the end of it's life.