publication

TROUBLESHOOTING

WIRED

REMOTE SENSORS

Note

: The diagram below shows how to attach an isolation relay to

the “W” or “Y” circuit to provide constant power on power stealing

thermostats. This willl allow the thermostat to operate properly with

a remote sensor.

Figure 1 shows a single transformer heating/cooling system, with

isolation relays installed in the heating (

) and cooling (

) circuits.

To simplify the diagram, limit and safety switches are not shown

here, although they will be found either in the low or high voltage

circuit. Limit and safety switches

must be retained

. Refer to the

equipment manufacturer’s system wiring diagram for the location of

limit and safety switches.

* Isolation Relay Wiring

Transformer

Red Jumper Wire

THERMOSTAT

24 VAC

Line

Voltage

Figure 1. Wiring for single transformer systems

RH W Y

Heating

System

Cooling

System

WARNING

DO NOT REMOVE OR WIRE AROUND LIMIT

AND SAFETY SWITCHES WHEN INSTALLING

ISOLATION RELAYS.

temperature is steadily dropping, reading low, or reads

08°

, or displays – – – (3 dashes) when a remote sensor is installed,

it can be traced to one of the three following conditions.

Troubleshooting Chart

To function correctly and read temperature accurately, the thermostat must have constant 24-volt power. If the thermostat

Condition

Test

Comments

1. Loss of 24-volt power. On models with batteries, remove the batteries and re-install

For the sensor to read correctly,

thermostat. If the display is blank, check heating and cooling the 24-volt system power

must

system to determine why 24-volt power is absent.

be present. Some systems may

require an isolation relay* to

provide constant power to the

thermostat. Limit or safety

devices in the equipment can

also cause a power interruption.

2. A broken wire on S1,

Disconnect sensor wires at thermostat. Attach a short piece Repair or replace the 3 wire

S2 and S3 or (+, SA, -) (2') of three-wire shielded cable to S1, S2 and S3 or (+, SA,

shielded cable. Be sure the

from the thermostat to -) on the subbase. Bring the remote sensor to the thermostat remote wire run is not parallel

the remote.

location and attach S1, S2 and S3 or (+, S, -) respectively.

to line voltage wires that carry

Reattach thermostat. If the temperature begins to climb

heavy inductive loads, or across

(slowly), it is reading correctly. If it reads correctly with the 2'

fluorescent light ballasts that

length but improperly when attached to the wire run, it

may cause an inductance to be

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3. A shorted or

Because it is an electronic sensor, there are no Ohm values Replace remote sensor.

damaged remote sensor. to test. If correct conditions as listed in 1 & 2 above and the

temperature stays at or near 08°, it indicates a shorted or

damaged remote sensor.

Note: Digital thermostats and remote sensors acclimate very slowly to temperature change. It may take an hour or more for

the temperature to acclimate to the room temperature from a low temperature reading as outlined above. To expedite the

room temperature display use the reset instructions listed in the installation instructions for the thermostat model you are

working with. When reset, the thermostat will default to a room temperature of 70° and begin sensing room temperature. Be

sure to reconfigure the installer menu for a remote sensor because the reset function may cancel remote sensing.

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