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51
The dehumidification output, DHUM on the Thermidistat should
be connected to the furnace control thermostat terminal DHUM.
When there is a dehumidify demand, the DHUM input is
activated, which means 24 vac signal is removed from the
DHUM input terminal. In other words, the DHUM input logic is
reversed. The DHUM input is turned ON when no dehumidify
demand exists. Once 24 vac is detected by the furnace control on
the DHUM input, the furnace control operates in Thermidistat
mode. If the DHUM input is low or OFF for more than 48 hours,
the furnace control reverts back to non-Thermidistat mode.
The cooling operation described above also applies to operation
with a Thermidistat. The exceptions are listed below:
a. When the R to G-and-Y1 circuit is closed and there is
a demand for dehumidification, the furnace blower
motor BLWM will continue running at low-cool speed
(same speed as LO HT).
b. When the R to G-and Y/Y2 circuit is closed and there
is a demand for dehumidification, the furnace blower
motor BLWM will drop the blower speed from COOL
to HI HT for a maximum of 10 minutes before
reverting back to COOL speed. If there is still a
demand for dehumidification after 20 minutes, the
furnace control CPU will drop the blower speed back
to HI HT speed. This alternating 10-minute cycle will
continue as long as there is a call for cooling.
c. When the “call for cooling” is satisfied and there is a
demand for dehumidification, the cooling blower-off
delay is decreased from 90 seconds to 5 seconds.
A00275
Fig. 50 -- Two-Stage Furnace with Single-Speed Air
Conditioner
A00276
Fig. 51 -- Two-Stage Furnace with Two-Speed Air
Conditioner
A00277
Fig. 52 -- Two-Stage Furnace with Single-Speed Heat Pump
(Dual Fuel)
58MEC