L4064B2236 controls high limit and fan motors in forced air heating systems. Turns fan on and off according to plenum temperature via helical bimetal sensing element.
Application:
These combination warm air fan and limit controllers are suitable for various types of forced air heating systems. The controllers have 2 switches; one which opens the limit circuit if the plenum temperature exceeds the preset safety limit; it resets automatically. The other switch turns the fan on and off. The fan is turned on and off according to plenum temperature. The L4064R has a special high temperature range suitable for gravity heating systems. All models may be used as limit controllers by wiring only the limit side. Limit contacts are suitable for both line voltage and low voltage. For low voltage applications, the brass jumper must be removed."
Operation:
As the plenum temperature rises, the coiled bimetal sensing element of the control warps and mechanically makes the fan contacts (at the FAN ON temperature setting). During normal operation, the call for heat ends before the LIMIT setting is reached and the fan contacts break as the plenum temperature falls and the FAN OFF setting is reached. If the call for heat continues until the temperature in the plenum rises to the LIMIT setting, the bimetal element will mechanically break the limit contacts and de-energize the heating control circuit.
Here is the install document below that I got that info from. I have to run right now but will take a look later.
https://customer.honeywell.com/resources/Techlit/TechLitDocuments/69-0000s/69-0115.pdfI believe the problem you have to battle is if the plenum temp is too high and the thermostat for your living space is not calling for heat then it has to reject heat some how so it turns the fan on to cool the plenum. More to follow.
Edit, take a look at page 4 under "Checkout".
"When installation is complete, disconnect the fan motor circuit at the L4064. Turn on power and set thermostat to call for heat. Burner should come on and limit controller should shut burner off when plenum temperature reaches the limit set point. Turn off power, reconnect the fan switch, turn on power and again set thermostat to call for heat. The fan should start when plenum temperature has reached fan-on setting."