Settings; Mount Thermostat; Set The Heat Anticipator; Installation Of Locking Cover Assembly - Honeywell T874 Product Data

8. Move the HEAT and COOL levers to the maximum tem-
perature desired.
9. Slide the stop brackets until one rests against the HEAT
lever and the other against the COOL lever.
10. Firmly tighten the mounting screw.
11. If the HEAT and COOL levers are to be locked in place
at a specific temperature, use the two insulated head
screws supplied instead of the two adjustable lever stop
brackets.
CAUTION
Equipment Damage Hazard.
Do not use standard screws that provide metal-to-
metal contact with the stop brackets. Short circuit and
potential equipment damage can result.

Mount Thermostat

1. Remove the thermostat cover by pulling the bottom
edge of the cover away from the base until it snaps free
of the cover clip.
NOTE: The cover is hinged at the top and must be removed
by pulling up at the bottom.
2. Carefully remove and discard the polystyrene packing
insert that protects the mercury switches during ship-
ment.
3. If LED indication (EM.HT., CHECK, etc.) is to be used
with the Q674 Subbase, install the preprinted insert
under the thermostat setpoint scale. To install, push
both thermostat setpoint levers to the far ends of the
thermostat. Use index finger to gently pull out the plastic
setpoint scale about 1/4 in. (6 mm). Position the desired
preprinted insert in the space above the LED lights.
Reposition setpoint levers.
4. Turn over the thermostat base and note the spring fin-
gers that engage the subbase contacts. Make sure the
spring fingers are not bent flat, preventing proper elec-
trical contact with the subbase.
5. Set the heat anticipator indicator(s) to the respective
current setting of each stage. See Set The Heat Antici-
pator section.
6. If the thermostat provides optional locking cover assem-
bly, start the Allen locking screws in the cover with the
wrench provided. See Fig. 10.
7. Note the two tabs along the top inside edge of the ther-
mostat base. The tabs fit into corresponding slots on top
of the subbase. Mount the thermostat on the subbase.
8. Align the two captive mounting screws in the thermostat
base with the posts on the subbase. Tighten both
screws. Do not overtighten screws or damage to sub-
base posts can result.
T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES
Fig. 10. Installation of locking cover assembly.

SETTINGS

CAUTION
Equipment Damage Hazard.
On systems using a gas valve, never apply a jumper
across the valve coil terminals, even temporarily. This
can burn out thermostat heat anticipator(s).

Set the Heat Anticipator

Move the indicator to match the primary control current draw.
When using a T874 Thermostat with two stages of heating,
set each heat anticipator to match its respective primary
control current draw. If you cannot find the current rating on
the primary control, or if further adjustment is necessary, see
NOTE and use the following procedure to determine the
current draw of each stage.
The current draw of each heating stage must be measured
with the thermostat removed and power on to the heating
system.
1. Connect an ac ammeter of appropriate range between
the heating terminals of the subbase:
a. Stage 1—between W1 and RH or R;
b. Stage 2—between W2 and RH or R
c. Stage 3—between W3 and RH or R.
2. Move the system switch to HEAT or AUTO.
3. After one minute, read the ammeter and record the
reading:
a. Stage 1—__________A;
b. Stage 2—__________A;
c. Stage 3—__________A.
NOTE: If equipment cycles too fast, set the indicator to a
higher current rating, but not more than one-half divi-
sion at a time, and recheck the cycle rate. Most con-
ventional two-stage heating equipment is designed
to operate at three cycles per hour per stage, and
one-stage heating equipment at six cycles per hour,
at 50 percent load conditions. When using the T874
Thermostat in heat pump systems, set the heat antic-
ipator at 140 percent of the actual primary control
current draw to reduce the cycling rate. See Fig. 11.
11
ALLEN
RETAINING
SCREWS (2)
M956
60-2485—8