Honeywell T874 Benutzerhandbuch

60-2485—8

12

Most heat pump systems should cycle 2-1/2 to 3 times per hour.

4. Hang the upper edge of the thermostat cover on top of 

the thermostat base and swing the cover downward 

until it engages with the cover clip.

Move the heating and cooling levers to the desired comfort 

positions. See Fig. 12. On some models with two stages of 

heating or cooling, the same lever controls both stages. The 

minimum differential between heating and cooling setpoints is 

4°F (2°C) (5°F [3°C]) on T874W. 

If model has optional screws to lock temperature control 

levers, loosen these screws before making temperature 

adjustment; tighten the screws when levers are set at desired 

position.

The subbase switching positions control the system operation 

as described below.

SYSTEM SWITCH (see subbase for positions):

OFF—both the heating and cooling systems are off. If the 

fan switch is at the AUTO position, the cooling fan is 

also off.

HEAT—heating system is automatically controlled by the 

thermostat. Cooling system is off.

AUTO—thermostat automatically changes between heat-

ing and cooling system operation, depending on the 

indoor temperature.

COOL—cooling system is automatically controlled by the 

thermostat. Heating system is off.

EM.HT.—emergency heat relay is automatically controlled 

by the thermostat. Cooling system is off. Compressor is 

de-energized.

SUPL.HT.—supplemental heat relay is energized. Cooling 

system is off. Compressor is de-energized.

WOOD—heating system is operating with only the wood-

burning stage.

OIL—heating system is operating with only the oil-burning 

stage.

WOOD/OIL—wood and oil stages operate sequentially; 

first the WOOD stage operates, then the OIL stage 

operates if the WOOD stage cannot handle the load.

EVAP—controls cooling system by water evaporation; see 

equipment instructions for further information.

OVERRIDE—night setback is disabled.

ON—heating system is controlled by the thermostat. EM. 

HT. or SUPL. HT. relay is not energized.

FAN SWITCH positions control fan operation as follows:

ON or CONT.—fan operates continuously.

AUTO—fan operates as controlled by the thermostat in 

heat pump systems or conventional cooling mode; fan 

operates as controlled by the plenum switch in conven-

tional heating mode.

LO—fan operates constantly at low speed.

MED—fan operates constantly at medium speed.

HI—fan operates constantly at high speed.

To move the subbase switches to the desired control 

positions, use thumb and index finger to slide the lever. The 

lever must stop over desired function indicator position for 

proper circuit operation.

Spring return momentary position switching feature is 

available on selected subbase models. On these models, the 

fan switch is positioned to the right of the system switch. By 

moving the fan switch to the far right and releasing it, the ON 

position circuit makes. The lever springs back on release. This 

position is not marked on the subbase.

The adjustable interstage differential feature, on a selected 

T874D model only, can be identified by the scale and tension 

screw near the heating and cooling mercury switches. See 

Fig. 13. On this model, the number of degrees between the 

making of the first and second stage mercury bulbs is 

adjustable. This feature is especially useful if the first stage 

controls the comfort temperature, and the second stage 

controls the energy savings temperature. Timers, such as the 

S6005, for insertion between the first and second stage 

control points must be ordered separately.

Each mark on the scale represents 1°F (0.6°C) The 

differential is factory set at 2°F (1°C) the differential can be set 

as high as 12°F (7°C) To set the adjustable interstage 

differential, loosen the tension screw. See Fig. 13. Slide the 

adjustable scale to align with the number of degrees desired 

between stages. Use the lower edge of the tension screw 

bracket as a guide for alignment. In heating, slide the lever 

wider apart for a larger differential, or closer together for a 

1.2

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MOVE INDICATOR TO
MATCH CURRENT RATING
OF PRIMARY CONTROL

STAGE ONE
ANTICIPATOR
HEATING 
CONTROL

STAGE TWO
ANTICIPATOR
HEATING CONTROL

M5069

STAGE 1
HEATING

STAGE 3
HEATING

STAGE 2
HEATING

HEATING
LEVER

COOLING
LEVER

STAGE 1
COOLING

STAGE 2
COOLING

CAPTIVE
MOUNTING
SCREWS (2)

M7625