Thermo Pride CLQS1-050T36N Installation And Operation Manual page 45

All installations and services must be performed by qualified service personnel.
O. TWINNING
When twinned, the circulating blower speeds are synchronized between the furnaces. If either furnace
has a need to run the blower, both furnaces will run the blower on the same speed. The cooling speed
has highest priority, followed by heating speed and fan speed.
Field installation of twinning consists of connecting wires between the "C" and "Twin" terminals of the
two controls. The 24 VAC secondary of the two systems must be in phase. All thermostat connections
are made to one control only.
The twin without thermostat connections is to have the call for heat supplied by an external isolation relay
to prevent its rollout switch from being bypassed by the other twin. The coil of the isolation relay
connects from the thermostat "W" to 24 VAC common. The contacts of the relay connect "R" to "W"
on the non-thermostat twin.
Failure to establish flame, an open limit switch, or undesired flame on one furnace shall not affect the
other furnace except for the possibility of causing its fan to run.
The blower off delay times and the continuous fan speed MUST BE the same on both controls.
43