Changeover; Changeover Conversion; Changeover Calibration; Changeover Calibration Check - Honeywell CONVERTASTAT TP970 Series Replacement Data

Changeover

TP971 and TP972 thermostats have changeover
features. The TP971 has day/night changeover and the
TP972 has summer/winter changeover. TP971 controls
direct acting at day setting with 13 psi (90 kPa) main air
pressure and direct acting at the lower night setting with
18 psi (124 kPa) main air pressure. The TP972 controls
reverse acting (RA) for summer cooling at 13 psi
(90 kPa) main air pressure and direct acting (DA) for
winter heating at 18 psi (124 kPa) main air pressure.
The branchline pressure (BLP) drops as the temperature
drops when the thermostat is operating DA. The BLP
drops as the temperature rises when the thermostat is
operating RA.

Changeover Conversion

On some systems the lower main air pressure is higher
(14 or 15 psi [97 or 103 kPa]) so the changeover point
must be raised. On these systems, turn the changeover
adjustment screw (Fig. 9) one-half turn clockwise for
each 1 psi (7 kPa) over 13 psi (90 kPa).
TP971 or TP972 thermostats used on systems having
16/21 psi (110/145 kPa) or 13/16/21 psi (90/110/145 kPa)
main air pressure require a different spring for proper
changeover operation. Change the spring as follows:
1. Remove thermostat from backplate if mounted.
2. Remove changeover adjustment screw (Fig. 9)
from thermostat back.
3. Replace gold-colored spring with silver-colored
spring furnished in TP971 kit. Order 14002373-001
Spring for TP972 conversion.
4. Reinstall changeover adjustment screw and set
flush with spring chamber top.
5. Mount thermostat on backplate again.
6. Follow procedures in Changeover Calibration
Check section and recalibrate if necessary.
FILTER COVER
THERMOSTAT
MULTISTAGE FILTER
CHANGEOVER
ADJUSTMENT SCREW
SPRING CHAMBER
DAY/AUTO LEVER
(TP971 ONLY)
Fig. 9. TP970 Series Thermostat—Back View.

Changeover Calibration Check

1. Set main air pressure to higher pressure setting
(night for TP971, winter for TP972A2192, and
summer for TP972A2200).
2. Using gage adapter, insert gage into gage tap (see
Fig. 8). If results in Steps 3 or 5 are incorrect, go to
the Changeover Calibration section.
3. TP971:
Turn day setpoint adjustment until setpoint
indicator reads approximately 10F (5.5C) degrees
above space temperature and set night setpoint
dial below space temperature. The gage should
indicate main air pressure. Push day/auto lever to
day (left) position; it should stay there and BLP
M B
S
C5411
TP970 SERIES CONVERTASTAT
should go to 0 psi (0 kPa).
TP972:
Turn setpoint adjustment until setpoint indicator
reads approximately 10F (5.5C) degrees above
space temperature. BLP should go to 0 psi (0 kPa).
4. Set main air pressure to lower pressure setting
(day for TP971, summer for TP972A2192, and
winter for TP972A2200). Use 16 psi (110 kPa) on
13/16/21 psi (90/110/145 kPa) systems.
5. TP971:
With day setpoint indicator and night setpoint dial
set as in Step 3, BLP should go to zero. Push
day/auto lever to day (left) position, it should return
to auto position when released.
TP972:
With setpoint indicator set as in Step 3, BLP should
go to main air pressure.

Changeover Calibration

1. Remove thermostat from wall.
2. Loosen screws. Remove backplate from wall but
do not disconnect tubes from backplate.
3. Plug thermostat into backplate.
4. Use following changeover procedures for calibra­
tion with or without a branch line pressure gage.
WITH BRANCHLINE PRESSURE GAGE
If thermostat changeover point was not correct at Step 3
of the Changeover Calibration Check procedure:
1. Use screwdriver end of thermostat tool to turn
changeover adjustment screw one-quarter turn
counterclockwise (see Fig. 10).
2. Make a calibration check.
3. Continue with one-quarter turn adjustments
followed by a calibration check until changeover
point is correct.
If thermostat changeover point was not correct at Step 5
of the Changeover Calibration Check procedure:
1. Use TP970 Series thermostat tool to turn
changeover adjustment screw (Fig. 10) one­
quarter turn clockwise.
2. Make a calibration check.
3. Continue with one-quarter turn adjustments
followed by a calibration check until changeover
point is correct.
Fig. 10. Location of Calibration Adjustment Screw
with Backplate Attached.
WITHOUT BRANCHLINE PRESSURE GAGE (TP971 ONLY)
1. Set system pressure to 18 psi (124 kPa) (night
pressure).
2. Hold the day/auto lever in day (left) position. Turn
changeover adjustment screw counterclockwise
until lever holds in place.
3. Release lever and slowly turn changeover
adjustment screw clockwise until lever snaps back
to auto position.
5
®
KITS
CHANGEOVER
ADJUSTMENT
SCREW
C183-3
85-0210EF—1