Carrier 58UXT Series Operating Instructions Manual Download Page 14

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2. Non-Adaptive Heating Mode—Two-Stage Thermostat and

2-Stage Heating
(See Fig. 16 for thermostat connections).

NOTE:

In response to thermostat call for heat R to W/W1 and

with HIGH HEAT ONLY switch SW1 set to OFF, the control
selects low-stage heating only with LOW HEAT switch SW2 set
to ON, or the control selects adaptive heating mode with LOW
HEAT switch SW2 set to ON. The control selects high-stage
heating only with HIGH-HEAT ONLY switch SW1 set to ON. In
response to thermostat call for high-stage heat R to W1 and W2,
the control selects high-stage heating regardless of switch SW1
and SW2 settings. See Fig. 15 for description of switch settings or
Fig. 16 for control circuit diagram.

The start-up and shutdown functions and delays described in item
1. apply to the 2-stage heating mode as well, except for switching
from low- to high-stage and vice versa.

a. When the wall thermostat

″

calls for heat

″

, R-W/W1 circuit

closes for low-stage or R to W1-and-W2 circuits close for
high-stage. The furnace control performs a self check,
verifies low-heat and high-heat pressure switch contacts
LPS and HPS are open, and starts inducer motor IDM in
low speed or high speed as appropriate.

b. Switching from low- to high-gas heat—If thermostat

R-W/W1 circuit for low-gas heat is closed and R-W2
circuit for high-gas- heat closes, the control CPU switches
the inducer motor IDM speed from low to high. The
high-heat pressure switch relay HPSR closes. When in-
ducer motor IDM provides sufficient pressure to close
high-heat pressure switch HPS, the high-heat gas valve
solenoid GV is energized. The blower motor BLWM
switches speed for high-gas heat 5 sec after R-W2 circuit
closes.

c. Switching from high- to low-gas heat—If thermostat R-W2

circuit for high-gas heat opens and R to W/W1 circuit for
low-gas heat remains closed, the control CPU will switch
inducer motor IDM speed from high to low. The high-heat
pressure switch relay HPSR will open to de-energize
high-heat gas valve solenoid GV. When inducer motor

IDM reduces pressure sufficiently, the high-heat pressure
switch HPS will open. The low-heat gas valve solenoid GV
remains energized as long as low-heat pressure switch LPS
remains closed. The blower motor BLWM switches speed
for low-gas heat 5 sec after R-W2 circuit opens.

3. Cooling Mode

a. Single-Speed Cooling Outdoor Unit

(See Fig. 15 for thermostat connections.)

(1.) The thermostat closes R to G-and-Y circuits. The R-Y

circuit starts the outdoor unit, and R to G-and-Y
circuits start the furnace blower motor BLWM on
high-cool speed.

(2.) The EAC terminals EAC-1 and EAC-2 are energized

with 115v when blower motor BLWM is operating.

(3.) When thermostat is satisfied, the R to G-and-Y circuits

are opened. The outdoor unit stops, and furnace
blower motor BLWM continues operating on high-
cool speed for an additional 90 sec.

b. Two-Speed Cooling Outdoor Unit

(See Fig. 16 for thermostat connections.)

(1.) The thermostat closes R to G-and-Y1 circuits for low

cooling or closes R to G-and-Y1-and-Y/Y2 circuits for
high cooling. The R to Y1 circuits start the outdoor
unit on low-cooling speed, and the R-G circuit starts

Table 6—Setup Switch Description

SETUP

SWITCH NO.

NORMAL

POSITION

DESCRIPTION

OF USE

SW-1

High Heat Only

OFF (Staged Gas Heat)

Turn switch on to obtain only high-gas-heat operation on

any call for heat regardless of whether R-W/W1, or