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TH 188 Unit Mounted Thermostats
Product Description
The TH 188 Unit Mounted Thermostat is a remote
bulb, gradual acting pneumatic instrument that
maintains a preselected room temperature by
positioning pneumatic devices that control heating or
cooling medium. This thermostat has a liquid filled
thermal system.
Product Numbers
Installation Instructions
Document No. 129-129
Rev. 3, August, 2000
TH 188R Reverse Acting (RA)
20 scim (5.5 ml/s) restrictor
TH 188HC Heating (direct)/Cooling
(reverse) 40 scim (11 ml/s) restricto r
TH 188D Direct Acting (DA)
40 scim (11 ml/s) restrictor
Replacement for Honeywell models
LP916BXXXX
Heating (direct)/Cooling (reverse)
40 scim (11 ml/s) restrictor
Replacement for Johnson Controls
T-3300-2
Heating (direct)/Cooling (reverse)
40 scim (11 ml/s) restrictor
Required Tools
•
Medium flat-blade screwdriver
•
Small drill
Expected Installation Time
90 minutes (1 hour and 30 minutes)
188-0024
188-0030
188-0031
188-0033
188-0034
Figure 1. Thermostat and Mounting Bracket.
NOTE:
If there is not enough room to mount the
thermostat in a convenient location, or if
the set point dial must be in the same
compartment as the fan switch, order an
extension shaft kit (Part Number 188-101).
Figure 2
See
Using the extension shaft, mount the
thermostat in any convenient location
within eight inches of the control
compartment.
.
Installation
A mounting bracket is included for mounting the
thermostat in various units.
1. Fasten the mounting bracket to the partition
with two sheet metal screws included with the
thermostat.
installation.
Figure 1
shows a typical
Figure 2. Use of Shaft Extension.
2. Mount the remote sensing bulb in the air stream
of the return air (near the inlet of the fan).
Avoid metal to metal contact between the bulb
and the unit to prevent damage to the soft
copper sensing bulb from unit vibration.
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Document No. 129-129
Installation Instructions
Rev. 3, August, 2000
Installation, Continued
3. Fasten the capillary and/or bulb in the return air
stream using the adhesive backed cable clip
included in the kit.
4. Make air connections to the "S" (supply) Port
and "R" (return) Port. Thermostats have a
barbed fitting for 1/4-inch (6.4 mm) O.D. poly
tubing.
Calibration
The thermostats are factory calibrated at 72°F
(22°C) and 7-1/2 psi (52 kPa) control pressure.
General
1. Determine the temperature at the remote bulb.
2. Set knob pointer to the temperature found. Dial
increments are approximately 5 degrees on the
major divisions with 1 degree subdivisions,
beginning at 60°F clockwise to 85°F.
3. Loosen (do not remove) return line test port
screw. Slip rubber line over test port and
connect to a test gauge (
Figure 3
).
Dual action
On the HC thermostat, calibration should be at
7-1/2 psi (52 kPa) for both DA and RA. The unit has
one thermal system with a reversing relay to give the
action desired. If calibrated at 7-1/2 psi (52 kPa) for
winter, the summer calibration will be 7-1/2 psi
(52 kPa). If 9 psi (62 kPa) is used for winter, 6 psi
(41 kPa) will be summer's calibrated pressure.
Figure 4
calibration points. If the same pressure is desired for
both seasons, the RA section of the thermostat
needs to be recalibrated (follow the RA calibration
procedures).
shows the relationship of the DA and RA
Figure 4. Dual Action Calibration Points.
Figure 3. Test Port and Gauge Used for Calibration.
4. With the knob pointer set at the temperature of
the remote bulb, the output (return line) pressure
should be 7 to 8 psi (48 & 55 kPa) for all models.
If the output pressure is not 7 to 8 psi (48 to
55 kPa), remove knob after loosening its set
screw. Then, rotate the set point adjustment
post until output pressure is 7 to 8 psi.
5. Replace knob and set pointer to temperature of
the bulb, lock, and then turn to desired setting.
The thermostat is now in calibration.
Single action
The direct acting or reverse acting thermostat may
be calibrated at any pressure. It is suggested that
7-1/2 psi (52 kPa) be used.
Reverse acting stage
Table 1
See
pressure.
Table 1. Air Supply Pressure and Changeover.
Type and
Model No.
Powers HC
(TH188HC)
Honeywell
HC (LP916B)
Johnson HC
(T-3300-2)
The reverse acting stage is factory adjusted and
does not require field adjustment. If the adjustment
is disturbed, re-adjust as follows:
1. With the main air supply set for 25 psi
(172 kPa), connect a Pressure Reducing Valve
(PRV) with gauge to the supply side of
thermostat and set at 25 psi (172 kPa).
2. Remove knob and cover from thermostat, as
shown in
3. Open bleed screw on test port and connect
gauge (
for air pressure and changeover
Heating
(Da)
25 psi
(172 kPa)
18 psi
(124 kPa)
20 psi
(138 kPa)
Figure 3
Figure 5
).
.
Cooling
(Ra)
18 psi
(124 kPa)
13 psi
(124 kPa)
15 psi
(103 kPa)
Changeover
(145 kPa)
(103 kPa)
(117 kPa)
21 psi
15 psi
17psi
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Siemens Building Technologies, Inc.
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Document No. 129-129
Installation Instructions
Rev. 3, August, 2000
Installation, Continued
Heat–cool thermostat changeover
Table 1
See
for air pressure and changeover
pressure.
The changeover is a factory adjustment; it is sealed
with ambroid and does not require field adjustment.
If, for some reason, this adjustment is disturbed, readjust as follows (See
Figure 5
):
1. Supply the thermostat with an air supply
pressure equal to the appropriate changeover
pressure (
Figure 5. Heating/Cooling Changeover.
4. Rotate adjustment post to give an output within
1/2 psi (3.4 kPa) of calibration pressure.
5. Adjust PRV for 18 psi (124 kPa) air supply;
observe the control pressure. If not within
1/2 psi (3.4 kPa) of calibration pressure, adjust
the reverse acting adjustment until it is. Apply
ambroid to the screw setting.
6. Remove test port gauge; close bleed screw.
7. Replace cover and knob.
8. Lock knob in place with pointer at bulb
temperature.
9. Set knob at desired temperature setting.
Table 2. Troubleshooting.
Complaint Check Possible Cause Corrective Action
Supply Air No Air As Required
Return line
pressure
0 psi
(0 kPa)
Return line
pressure
18 psi
(124 kPa) or
greater
Excessive cycling Lever assembly Sticking or binding of levers As required
Table 1
* See
*Heating
25 psi
(172 kPa)
*Cooling
18 psi
(124 kPa)
Supply Air Pressure Too High As Required
*Heating
25 psi
(172 kPa)
*Cooling
18 psi
(124 kPa)
for Honeywell and Johnson Controls pressures.
Calibration Out of calibration Recalibrate
Restrictor Clogged or dirty Clean or replace
Sensing element Loss of charge Replace sensing element
Direct acting stage Internal binding or leaking Replace thermostat
Calibration Out of calibration Recalibrate
Throttling pin Dirt built up around pin Clean or replace nozzle assembly
Reverse acting stage Internal binding or leaking Replace thermostat
Calibration Out of calibration Recalibrate
Throttling Pin Dirt built up around pin Clean or replace nozzle assembly
Direct acting stage Internal binding Repla ce therm osta t
Calibration Out of calibration Recalibrate
Restrictor Clogged or dirty Clean or replace
Sensing element Loss of charge Replace sensing element
Reverse acting stage Improperly adjusted Re-adjust
Reverse acting stage Internal leaks or binding Replace thermostat
2. With the exhaust adjustment (center screw)
backed out several turns, turn the switch spring
adjustment (outer screw) down snug, and then
back off until air can be heard bleeding out.
3. Turn the exhaust adjustment down snug and
back off approximately 1/8 turn.
4. Seal both screws with ambroid to prevent
further movement.
The installation is now complete.
Reference
Technical Inst ructions
TH 188-2
155-064P25
Table 1
).
Information in this publication is based on current specifications. The company reserves the right to make changes in specifica tions and
models as design improvements are introduced. © 2000 Siemens Building Technologies, Inc.
Siemens Building Technologies, Inc.
Landis & Staefa Division
1000 Deerfield Parkway
Buffalo Grove, IL 60089-4513
U.S.A.
Your feedback is important to us. If you have
comments about this document, please send
them to technical.editor@sbt.siemens.com
Document No. 129-129
Printed in the U.S.A.
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