Programmable Electronic Thermostat
(630-0640) Installation Faxback Doc. # 44979

This thermostat was not designed for use with Heat Pumps or Multistage
systems. If you are aware that your system is one of the foregoing, do
not attempt to install the thermostat. Instead, please return it,
undamaged, to your RadioShack store.

For systems other than 24 volt AC, a transformer and relay are needed. If you have a 3-wire hot water system, you must install an isolation relay. See ORDER INFORMATION.

If you have previously removed your present thermostat from the wall,
refer to the letters or labels for each wire connected to the thermostat.
If you have not, refer to the directions under Compatibility which will be found on page 4.

Mounting

1. Make sure the power to the furnace and/or air conditioner is turned
off either at your main fuse box or at the unit.

2. Remove the existing thermostat from the wall by removing any decorat-
ive cover or plate and the screws which hold the thermostat to the
wall.

Note: Take care when lifting the thermostat away from the wall that you
do not break or inadvertently disconnect any of the wires. If you
find that your old thermostat is attached to a junction box, there
is likely 120 VAC present. DO NOT proceed further. Call a
qualified electrician.

3. After recording the color of each wire and the letter of its terminal
on page 5 of this manual, remove each wire from your old thermostat.
As you remove the wire, have a piece of masking tape handy. Place
each disconnected wire onto the masking tape.

4. When all wires have been put onto the tape, place the tape on the
wall, temporarily so as to make sure the wires do not slip back into
the opening in the wall or get in the way while you lay out the holes
to mount the Micronta thermostat.

5. Open both doors of the new thermostat and place it against the wall so
that it is level and in a position which will allow you to bring the
wires through its frame and onto the screws on the right side of the
unit. Use a pencil to mark the position of the slot in each upper
corner of the frame and the smaller, round hole in each lower corner.

6. Using the appropriate type of screw and mounting device for your type
of wall, (plastic anchor, Molly bolts, etc), drill the proper hole for
the type of screw/anchor in each of the corners. Insert a screw into
each of the upper holes and tighten them partially into the wall.

7. Hang the thermostat on the partially inserted screws. Adjust the
level of the unit and tighten, but do not overtighten, the two screws.
Insert one more screw into either lower corner and secure it.

Wiring The Thermostat

Your old thermostat had letters or, in some cases, numbers, at each screw
terminal for each wire that was connected to it. These letters/numbers
should have been recorded on page 5 when you removed the thermostat.

1. Refer to the following chart. Match the letter or number of your old
thermostat with the appropriate letter of your programmable thermo-
stat. Also, not the need to retain or remove the factory installed
metal jumper over terminals B and R.

2. After each wire has been identified and the new terminal label noted,
loosen each screw in turn, slip the wire beneath the terminal and
tighten the screw, until all wires have been reconnected.

TWO/THREE and FOUR wire systems - DO NOT REMOVE JUMPER:

OLD THERMOSTAT FUNCTION MICRONTA THERMOSTAT
TERMINAL MARKED TERMINAL MARKED

G or F (FAN) G

Y or C (COOLING) Y

W or H (HEATING) W

RH, RC, R, M (POWER) B
V, VR, VC, or 4

LEAVE FACTORY JUMPER IN PLACE R

Note: In some three wire systems the R and B wires are connected
together. In that case, connect BOTH to the R terminal of the
Micronta Thermostat.

FIVE wire systems - REMOVE JUMPER:

OLD THERMOSTAT FUNCTION MICRONTA THERMOSTAT
TERMINAL MARKED TERMINAL MARKED

G or F (FAN) G

Y or C (COOLING) Y

W or H (HEATING) W

RC, V, VC, R (POWER) B

RH, M, VR, 4 or A (POWER) R

REMOVE FACTORY JUMPER BETWEEN B AND R

THERMOSTAT CHECKOUT

1. Verify that power to your heating/cooling system is on.

2. Check HEAT operation:

Enter a HEAT temperature 2 degrees above the room temperature.

Let the furnace cycle through one complete cycle.

If the display goes blank at any time during the cycle see the
TROUBLESHOOTING section.

3. Check COOL operation:

CAUTION: DO NOT run cooling unit if outdoor temperature is
below 60 degrees.

Enter an A/C temperature 2 degrees below the room temperature.

Allow the air conditioner to go through one complete cycle.

4. If after 24 hours of operation, the thermostat displays the incorrect
temperature, you must calibrate the thermostat. See the TROUBLE-
SHOOTING section.

If the above steps are completely successfully, your thermostat is
operating properly.

TroubleShooting

Because of the simplicity of this programmable thermostat, it will rarely
give you any concern. If it should fail to function properly, this
section will help you to get the unit back into service quickly.

SYMPTOM: Thermostat loses program
Procedure:

1. You may have a dead battery.

2. The POWER switch may have been accidentally switched to OFF.

SYMPTOM: No Display
Procedure:

1. Check to see that the POWER switch is ON.

2. Check main switches, fuses, and circuit breakers on heating equipment
to make sure it has power. The heating control circuit powers the
thermostat even when it is used to control air conditioning equipment.

3. Check the wiring connections to the thermostat.

4. Make sure your system uses 24V AC. The thermostat will not operate
on a millvolt system.

5. See symptom below "Display Goes Blank."

SYMPTOM: Display goes blank before or after a furnace burn cycle.
Procedure:

Your furnace is interrupting power to the thermostat. This is not a
problem. The 9-volt battery will be adequate to carry the program for
the entire heating season.

SYMPTOM: Display goes blank for several minutes during long furnace burn
cycle. Procedure:

The furnace is probably not operating properly. Check for dirty air
filters or blocked registers.

SYMPTOM: Incorrect Temperature Display.
Procedure:

1. Make sure that the thermostat has been on for at least two hours.

2. Place a room thermometer on the left side of the thermostat.

3. Open the left door of the thermostat.

4. Locate the small circular dial (Potentiometer). See Page 7.

5. Turn the dial clockwise to increase the indicated temperature, or
counterclockwise to decrease the indicated temperature. Each turn
should be made very slightly. After each turn, allow the thermostat
to stabilize for about 30 seconds.

6. Continue this procedure until the thermostat has the same temperature
reading as your room thermometer.

SYMPTOM: Noisy gas valve.

A. Humming noise with the gas valve not actually opening and closing.
Procedure:
1. Obtain a 250 ohm 20 watt resistor.

2. Place the resistor with two terminals on the gas valve.

B. Chattering noise with the gas valve sounding like it is opening and
closing.
Procedure:

1. Try the resistor solution in "A" above.

2. If the gas valve is still noisy, install an isolation relay.
See ORDER INFORMATION.

SYMPTOM: Furnace will not turn on.
Procedure:

First, check to see if your thermostat is operating properly.

1. With a voltmeter, measure the voltage between the red and white
terminals for heat (the black and yellow terminals for air
conditioning). There should be approximately 24-volts AC when
heat/air conditioning IS required. If this drop occurs, your
thermostat is operating properly, but you need to install an
isolation relay. See ORDER INFORMATION.

2. If the voltage drop does not occur, return the thermostat to your
place of purchase.

SYMPTOM: Furnace operates continuously.
Procedure:

1. Check the thermostat to see if it is wired properly, or check the
furnace air conditioning system to make sure they are operating
correctly.

2. Measure the voltage as described under the previous symptom.

SYMPTOM: Thermostat will not turn air conditioner on.
Procedure:

Check the circuit breaker on the air conditioner to make sure it has
power.

SYMPTOM: The thermostat will not let me make a temperature setting.

1. Check if you have already made 6 settings. A maximum of 6 settings
per day are available. The thermostat will not accept a seventh
setting.

2. Check if you have used all 8 available temperature combinations. A
maximum of 8 heating and cooling combinations is allowed in your
weekly program. The thermostat will not accept a ninth combination.
(LB/SM 10/30/97)