Carrier 48TC 04 Series Service And Maintenance Instructions page 59

Minimum heating entering air temperature
When operating on first stage heating, the minimum
temperature of air entering the dimpled heat exchanger is
50_F (10 _C) continuous and 45_F (7 _C) intermittent for
standard heat exchangers and 40_F (4 _C) continuous and
35_F (2 _C) intermittent for stainless steel heat
exchangers. To operate at lower mixed- - air temperatures, a
field- - supplied outdoor- - air thermostat must be used to
initiate both stages of heat when the temperature is below
the minimum required temperature to ensure full fire
operation. Wire the outdoor- - air thermostat OALT (part
no. HH22AG106) in series with the second stage gas
valve. (See Fig. 70.) Set the outdoor- - air thermostat at
35_F (2 _C) for stainless steel heat exchangers or 45_F (7
_C) for standard heat exchangers. This temperature setting
will bring on the second stage of heat whenever the
ambient temperature is below the thermostat setpoint.
Indoor comfort can be compromised when heating is
initiated using low entering air temperatures with
insufficient heating temperature rise.
Thermostat
TH1
W1
TH2
W2
Fig. 70 - - OATL Connections
Troubleshooting Heating System
Refer to Table 24 and Table 25 for additional
troubleshooting topics.
59
LCTB
W1
OALT
W2
C08442