I have a 3 year old Carrier oil fired furnace Model #58CMA105-12.
It appears to be a 84,000 BTU burner. Currently it only runs on one speed while the burner is operating and it definitely is a high speed. I have recently noticed that inside the furnace next to the fan is an on-off toggle switch that turns the blower on or off. This switch operates the blower independently of the thermostat.
I also noticed that when this switch is pressed, the fan runs about 3/4 of the speed of what it does when the thermostat calls for heat. I have also noticed that while the blower is running at this speed and I flip the switch on the thermostat that controls the fan from auto to on, the blower runs at full speed instead of 3/4 speed.
Inside the furnace their is a diagram with nozzle and pump pressure info amongst other things. I also noticed that there are two rows, one row says fan speed med-hi and the other says fan speed hi. Both have the same nozzle size and BTU rating and both have the same temperature rise numbers.
Can anyone confirm whether or not this furnace is equipped with a variable speed blower, but the thermostat in the house is a single speed stat and only "calls" for the hi speed?
any help would be appreciated. I am somewhat handy, could it be as simple as ordering a 2 stage thermostat and installing it?
If there is information that I have inadvertantly left out, please let me know and I will provide.