Honeywell T874A,D Thermostats Subbases Installation Guide

Honeywell T874A,D Thermostats Subbases Installation Guide

These T874A,D Zone Thermostats and Q674B,D,E Subbases provide 24 to 30 Vac temperature control in Honeywell Trol-A-Temp heating/cooling zone systems. See Table 1 for thermostat/subbase and system compatibil- ity; see Table 2 for thermostat specifications. For complete Honeywell Trol-A-Temp System specification and appli- cation information, refer to the system specification in- cluded with the control panel.

TABLE 1—THERMOSTAT/SUBBASE AND SYSTEM COMPATIBILITY

a Subbase not included with thermostat; order separately. 

a Subbase not included with thermostat; order separately. 

Operation

On a 2-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 are about 2° F [1° C] between stages so that the second stage makes only when the first stage cannot handle the load. This is the interstage differential.

Recycling Notice

This control contains mercury in a sealed tube. Do not place control in the trash at the end of its useful life. If this control is replacing a control that contains mercury in a sealed tube, do not place your old control in the trash. Contact your local waste management authority for instructions regarding recycling and the proper disposal of this control, or of an old control containing mercury in a sealed tube. If you have questions, call Honeywell at 1-800-468-1502.

Installation

WHEN INSTALLING THIS PRODUCT…

1. Read these instructions carefully. Failure to fol- low them could damage the product or cause a hazard- ous condition.
2. Check the ratings given in the instructions and on the product to make sure the product is suitable for your application.
3. Installer must be a trained, experienced service technician.
4. After installation is complete, check out product operation as provided in these instructions.

CAUTION

1. Disconnect power supply to prevent electrical shock or equipment damage.
2. To prevent interference with the thermostat linkage, keep wire length to a minimum and run wires as close as possible to the subbase.
3. Do not overtighten thermostat captive mount- ing screws, because damage to subbase threads can result.
4. Do not short across terminals of systems con- trols. This can burn out the thermostat heat anticipator.

LOCATION

Locate the subbase about 5 ft [1.5 m] above the floor in an area with good air circulation at average temperature. Do not mount the subbase where the thermostat may be affected by:

• drafts or dead spots behind doors and in corners.
• hot or cold air from ducts.
• radiant heat from sun, appliances or fireplace.
• concealed pipes and chimneys.
• unheated (uncooled) areas such as an outside wall behind the thermostat.

MOUNTING THE SUBBASE

The thermostat subbase can be mounted on a horizontal outlet box or directly on the wall.

1. To mount on a horizontal outlet box, install the sub- base on the outlet box as shown in Fig. 1. For a wall installation, hold the subbase in position and mark holes for the anchors (Fig. 2). Obtain wall anchors locally. Take care that the wires do not fall back into the wall opening. Set aside subbase. Drill two 3/16 in. [4.8 mm] holes and gently tap anchors into the holes until flush with the wall.
2. Pull electrical wires through the cover plate (if used) and subbase cable opening (Fig. 3). See Wiring the Sub- base section before pulling any wires.
3. Secure the subbase with the screws provided. Do not fully tighten the subbase screws.
4. Level the subbase using a spirit level, as shown in Fig. 3, and firmly tighten the subbase mounting screws. The subbase mounting holes allow minor out-of-level adjustments.

WIRING THE SUBBASE

All wiring must comply with local electrical codes and ordinances. Follow equipment manufacturer wiring in- structions when available. To wire subbase:

1. Connect wires to the subbase terminals. Refer to Figs. 6-10 for wiring diagrams of typical zone systems. A letter code is located near each subbase terminal for identi- fication. The terminal barrier permits straight or conven- tional wraparound wiring connection (Fig. 4).
2. Some Q674 Subbases have RC and RH terminals for isolated heating and cooling transformers. For zoning systems, jumper RC and RH terminals as shown in Fig. 5 and wire as single R terminal.
3. Firmly tighten each terminal screw.
4. Fit wires as close as possible to the subbase. Push excess wire back into hole.
5. Plug the hole with nonflammable insulation to prevent drafts from affecting the thermostat.

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