Trane · Furnace · Cooling

Cooling and heat pump calls on S8 furnace control

S8B1S8X1S8X2

What happens, in order

Thermostat R-Y1-G closes and 24 V arrives at Y1 and G
24 V goes to the outdoor unit through the thermostat wiring
Indoor blower ramps to cooling airflow; display shows CP1 (S8B1/S8X1) or CL1 (S8X2)
Second stage R-Y2 closes, 24 V goes to the outdoor unit, and the blower ramps to second-stage airflow (CP2 or CL2)
Satisfied the outdoor unit stops and the blower stops unless a blower cool off delay is set in the menu; display returns to IDL
On S8X2 with a heat pump, the factory Y1-O jumper must be removed for the right display and operation; with the jumper in, the display reads CL1
On S8X2 for cooling, the jumper must stay in or the display reads HP1

Timings and thresholds

Item	Value
EAC relay delay	about 2 s after blower starts
HUM relay delay	about 1 s after blower starts

Codes you may see during this

CP1 CP2 CL1 CL2 HP1 HP2 tP3 tP7 IDL

Applies to: S8B1, S8X1 and S8X2 furnaces

Models

S8B1S8X1S8X2

More Trane furnace sequences

First-stage gas heating · Heating
Heating call sequence of operation · Heating
Heating sequence of operation · Heating
Second-stage gas heating (S8X2 only) · Heating
Cooling fan-off delay · Cooling

Trane error codes · Trane tips · Trane parts · All Trane sequences

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Source: Trane S8B1/S8X1/S8X2 installation 18-CE14D1-1A-EN, Sequence of Operation pp.59-61. Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.