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HVAC Tech Support Thermostats & Controls Advanced Programming Tips

 Basic operation of input

 Nesting programs

 Auxiliary output / Economizer output

 Connect to external timeclock

 Existing Energy Management System

 Light Sensor

 Motion Sensor

 Linai Sensor (open door or window)

Installation Instructions

External Timeclock
To control thermostats using an external timeclock, simply connect the two wires from the relay output on the timeclock to CK1 and CK21 on the thermostat. Whenever the timeclock relay is energized, the thermostat will go to Occupied. IN most cases an isolation relay should be used between the timeclock and the thermostat isolate their respective transformers. See wiring diagram below and notes below.

Note: When using the auxiliary input (CK1 & CK2) or if attempting to control multiple HVAC units with a single thermostat, it is possible to encounter transformer phasing problems that will interfere with thermostat operation. Connecting transformers that are not phased properly may result in a direct short, which could damage the transformers and/or the thermostat. Phasing problems are more likely if the units share a common ground with grounded secondary transformers.

Solution: If possible, phase all HVAC units together. If phasing is impractical, isolation relays may be used to isolate the transformers. To isolate the auxiliary input, use a separate transformer for the auxiliary control device (usually a timeclock). Connect the control device to an isolation relay coil*. Connect one set of isolated contacts to each thermostat at CK1 and CK2. See diagram A.

To prevent phasing problems when controlling multiple HVAC units with one thermostat, phase the HVAC units or use isolation relays* to isolate the unit transformers. One unit will be connected directly to the thermostat, and it will power the stat. All other units will require one set of isolated contacts for each of the following: heat, cool, fan, and/or reversing valve, etc. See diagram B.

* There is an optional accessory available that can be used instead of an isolation relay - it is an opto-coupler, which isolates voltage using an LED. It is wired exactly like a relay.

Energy Management System (EMS)
Most Energy Management systems will include some type of dry-contact or relay output. To control the thermostat, connect CK1 and CK2 from the thermostat to the desired relay output. Polarity of the wires does not matter. When the EMS relay is closed, the thermostat will control to the Occupied setpoints. When the relay is open, the thermostat will revert to normal operation.

Light Sensor - External Sensor
Connect the two control wires from the light sensor to the CK1 and CK2 terminals on the thermostat. ***Power?***

Light Sensor - Internal sensor - (T2900)
The light sensor is built in to the thermostat. The light sensor is adjustable to accommodate different light levels. The sensor adjustment screw is located in the inner cover of the thermostat near the down arrow button. A small screwdriver is included with the thermostat. Turning the screw clockwise increases the sensitivity, counterclockwise decreases the sensitivity. The light sensor responds to overhead light only, so it is not affected by side windows. The minimum light level that will put the thermostat into occupied mode is approx. 24 fcd at the highest sensitivity setting, and approx. 96 fcd at the lowest sensitivity setting. The easiest way to test light level is to use a flash meter from a camera store, such as the Minolta Flash Meter V. Make sure to test the light level right up against the wall where the thermostat will be mounted.

Whenever the thermostat senses light, it is forced into Occupied 1. The thermostat must be in Program On mode to use the light sensor, in all other modes the sensor is ignored. When the lights are off, the thermostat reverts to its regular program, which allows programming of morning warm-up, different setpoints, etc.

Morning warm-up: It may be desirable to start the heating (or cooling) in the morning before the building is occupied in order to have the building comfortable by the time the occupants arrive. This is easy to do with the light activated thermostats, just use the regular program and set any of the Occupied periods for the desired time and setpoint. When the occupants arrive and turn on the lights, the stat will be forced into Occupied 1. For example, if the desired normal occupied temperature is 72 degrees and the building is occupied at 8 am, set Occupied 1 to start at 7am and end at 8am with a setpoint of 72 degrees. This will provide one hour of morning warm-up. If the lights are not on at 8 am, the thermostat will go to Unoccupied. If the lights are on, the stat will go to Occupied 1 at 72 degrees and stay there as long as the lights remain on.

Different setpoints: It may be desirable to have two (or more) different setback temperatures, based on the time of day. For example, consider a building that is normally occupied from 8 am to 5 pm. The building owner wishes to save energy by using a light activated stat to set the temperature back when the offices are unoccupied (lights are off). The owner sets the cooling Occupied setpoint to 72 and the cooling Unoccupied setpoint to 85. Now, whenever the lights are off, the thermostat will go to Unoccupied at 85 degrees. But, if an office worker goes to lunch just for an hour (and the lights are off during that time), he/she may not want to return to a room that's 85 degrees! In this case, simply set Occupied 2 to run from 8 am to 5 pm at 75 degrees. Whenever the lights are on, the stat will go to Occupied 1 at 72 degrees, because Occupied 1 overrides Occupied 2. When the lights are off, if it is between 8 and 5 the stat will revert to Occupied 2 at 75 degrees, giving a 3 degree setback which will save energy without allowing to room to heat up too much.

Motion Sensors
To connect a motion sensor to the input of a thermostat, use a motion sensor with a relay or dry contact type output and a timer that will keep the sensor on for a length of time after motion is detected. The timer is necessary so that the sensor doesn't require constant motion, just occasional movements. Most motion detectors are infrared devices and require a 9 - 12 VDC power source. See Appendix A for model numbers and sources.

Connect the power source to the motion detector, then run two wires from the Normally Closed contacts on the sensor to the CK1 and CK2 terminals on the thermostat (polarity doesn't matter.) Whenever the sensor detects motion it will close its relay, which will put the thermostat into Occupied mode.

Appendix A
This sheet contains a few sources for the purchase of products in the preceding document. Model numbers and prices are included where possible. Prices are approximate - contact vendor for current prices. Author makes no claims as to the operation, availability, or cost of the items listed below - this list is for informational purposes only.


Radio Shack
1 (800) THE-SHACK

Home Controls
1 (800) 266-8765
7626 Miramar Road, Suite 3300
San Diego, CA 92126

Home Automation Systems, Inc.
1 (800) SMART-HOME
151 Kalmus Drive, Suite L 4
Costa Mesa, CA 92626-5979

Remote Control Activator (on/off relay)
Radio Shack
RSU 10037752 $18.99

Home Controls
XT506 $20.95

Home Automation Systems, Inc.
2010 $20.95

Telephone Responders (requires remote control activator, above)

Radio Shack
RSU 10037778 $79.99

Home Controls
HCTMS $169.95
XT551 $67.95

Home Automation Systems, Inc.
5000 $64.95

Contact switch (for door or window)
  Radio Shack Home Controls Home Automation Systems
Pressure-type 49-513 $1.49 US220SP $6.95  
For sliding door or window 49-518 $4.99    
Magnetic type - normally closed 49-532 $4.99 US130SP $4.95 7113 $3.95
Magnetic type - normally open 49-533 $5.99 US131SP $4.95  
Other types available.

Motion Sensors

Home Controls
RK7001 $21.95

Home Automation Systems
7481 $24.99

Wireless Motion Sensor
7402 $129.95 motion sensor (transmitter)
7412 $47.95 receiver

HVACWebsite makes no guarantee on any of the prices.