These thermostats and subbases provide 24 to 30 Vac control for two-stage heating and one-stage cooling heat pump systems as follows:
MODEL | CHANGEOVER | SYSTEM SWITCHING | FAN SWITCHING |
Y594G (T874G/Q674F) | Automatic (Heat or Cool) | OFF-EM.HT.-HEAT- AUTO-COOL | AUTO-ON |
T874R/Q674L | Manual | EM.HT.-HEAT-OFF-COOL | AUTO-ON |
On a two-heat thermostat, the two stages of heat “make” sequentially as the temperature drops. “Make” refers to the mercury switch initiating a call for heat or COOL There is about 2 F [1 .I C] between stages so that the second stage (auxiliary heat) makes only when the first stage can’t handle the load. This is the interstage differential. Three LEDs (light-emitting diodes) are included on the sub-base. The red CHECK LED lights when something needs to be checked or done to maintain the efficient operation of the system. See your heating system instructions to find out specifically what the CHECK LED signifies. The green LED lights when the AUX. HT. stage (second stage) heat is operating. The red EM.HT. LED lights when the EM.HT. relay is energized, usually operating electric strip heaters.
WHEN INSTALLING THIS PRODUCT. . .
MOUNTING THE SUB BASE
The thermostat subbase can be mounted on a vertical outlet box, horizontal outlet box, or directly on the wall.
CAUTION
LOCATION
Install the thermostat about above the floor in an area with good circulation at an average temperature. Do not install the thermostat where it may be affected by-
For a wall installation, hold the subbase in position and mark holes for anchors (Fig. 2). Wall anchors must be obtained from the local hardware store. Take care that the wires do not fall back into the wall opening. Set subbase aside. Drill four 3116 in. [4.8 mm] holes and gently tap anchors into the holes until flush with the wall.
Pull wires through the cover plate (if used) and subbase cable opening (Fig. 3). Secure the cover plate (if used) and subbase with the screws provided. Do not fully tighten the subbase screws.
Fig. 4-Internal schematic and typical hookup of T874G and Q674F in the heat pump system
Fig. 5-Internal schematic and typical hookup of T8?4R and Q674L in the heat pump system
Level the subbase using a spirit level, as shown in Fig. 3, and firmly tighten the subbase mounting screws. The subbase mounting holes provide for minor out-of-lever adjustments.
WIRING THE SUBBASE
All wiring must comply with local electrical codes and ordinances. Follow the equipment manufacturer’s wiring instructions when available. To wire the subbase, proceed as follows:
TEMPERATURE SETTING COOL
cooling system is controlled by the thermo-On the T874G, move the heating and cooling set point stat. Heating system is off. levers to the desired positions. The minimum differential AUTO (T874G only)-thermostat automatically between heating and cooling set points is 3 F [1.7 C]. On changes between heaat nd cool modes, depending the T874R one lever controls both heating and cooling. upon the indoor temperature.
SUBBASE SETTING
System switching positions control thermostat operation as follows: EM. HT.-emergency heating system is energized. Red EM. HT. LED on subbase is on. Cooling system is off. HEAT-heating system is controlled by the thermostat. Cooling system is off. OFF-both the heating and cooling systems are off. Fan switching positions control fan operation as follows: ON-fan operates continuously. AUTO-fan operates with equipment as controlled by the thermostat. To switch positions, use thumb and index finger to slide lever to desired position. Switch lever must stop in detent directly over desired function indicator mark for proper circuit operation.
HEATING
Move the system switch on the subbase to HEAT and the fan switch to AUTO. Move the heating set point lever on the thermostat about 10 F [56 C] above room temperature. Heating should start, providing there is no time delay or out door temperature limiting system, and the fan should run after a short delay. Move the heating set point lever about 10 F [56 C] below room temperature. The heating equipment should shut off, and the fan should run for a short time, then shut off. Move the system switch on the subbase to COOL. Move the cooling set point lever on the thermostat about 10 F [56 C] below room temperature. The cooling equipment and fan should start. Move the cooling set point lever about 10 F [5.6 C] above room temperature. The cooling equipment and fan should stop.
NOTE: On the T874R, the same lever controls both heating and cooling.
FAN
Move the sub base system switch to OFF, and the fan switch to ON. The fan should run continuously. When the is in the AUTO position, fan operation is controlled by the heating or cooling system
These thermostats are accurately calibrated at the factory. THEY DO NOT HAVE PROVISION FOR FIELD CALIBRATION. THERMOMETER The thermometer in your thermostat has been accurately calibrated at the factory. The thermometer should only need adjustment if it has been dropped or shifted due to mishandling. If set point lever and the thermometer reading do not agree, follow the procedure below.
Honeywell Inc.
1885 Douglas Drive N.
Golden Valley, MN 55422-4386
international sales offices in all principal cities of the world. Manufacturing in Australia, Canada, Finland,
France, Germany, Japan, Mexico, Netherlands, Spain, Taiwan, United Kingdom, U.S.A
PRINTED IN U.SA
Download Manual:
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