Technical Instructions Document No. 155-064P25 TH 188-2 February 3, 2022 PowersTM Controls TH 188 Unit Mounted Thermostat Description The TH 188 Unit Mounted Thermostat is a remote bulb, gradual acting pneumatic instrument that maintains a pre-selected temperature by positioning pneumatic devices that control a heating or cooling medium. Replacement thermostats are available for Honeywell models LP916Bxxxx and Johnson Controls model T-3300-2.
Technical Instructions Document Number 155-064P25 February 3, 2022 Specifications Operating Physical TH 188 Unit Mounted Thermostat Control action Heating (DA) and Cooling (RA) Direct acting only Reverse acting only Operating range 60° to 85° F (16° to 29° C) Operating pressure 30 psi (207 kPa) max. Sensitivity range 1 to 5.25 psi per degree F (12 to 65 kPa per degree C) Factory sensitivity setting 2.25 psi per degree F (28 kPa per degree C) Temperature response 0.2° F (0.
TH 188 Unit Mounted Thermostat Accessories Operation (See Figure 1). Heating, Direct Acting, 25 psi (172 kPa) Supply Technical Instructions Document Number 155-064P25 February 3, 2022 Extension shaft Remote bulb mounting kit Limit stop kit (25 sets/kit) Restrictor replacement kit five 20 scim (5.5 ml/s) and five 40 scim (11 ml/s) Thermostat mounting bracket 188-101 808-517 188-144 188-159 188-077 NOTE: Pressures used refer to thermostats calibrated to Powers pressures.
Technical Instructions Document Number 155-064P25 February 3, 2022 TH 188 Unit Mounted Thermostat Operation, continued Figure 1. Thermostat Operation. Calibration General The thermostats are factory calibrated at 72° F (22° C) and 7-1/2 psi (52 kPa) control pressure. 1. Determine the temperature at the remote bulb. 2. Set pointer to the temperature found. Dial increments are approximately five degrees on the major divisions with one degree subdivisions, beginning at 60° F clockwise to 85° F. 3.
TH 188 Unit Mounted Thermostat Calibration, continued Single Action Dual Action Technical Instructions Document Number 155-064P25 February 3, 2022 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. On the HC thermostat, calibration should be at 7-1/2 psi (52 kPa) for both DA and RA. This is due to the use of one thermal system and a reversing relay to give the action desired.
Technical Instructions Document Number 155-064P25 February 3, 2022 Calibration, continued Heat-Cool Thermostat Changeover TH 188 Unit Mounted Thermostat See Table 1 for air pressures and changeover pressures. The changeover is a factory adjustment; it is sealed with thread locker and does not require field adjustment. If for some reason this adjustment is disturbed, re-adjust as follows: (See Figure 4) 1. Supply the thermostat with an air supply equal to the appropriate changeover pressure. 2.
TH 188 Unit Mounted Thermostat Technical Instructions Document Number 155-064P25 February 3, 2022 Installation, contintued Figure 5. Unit Mounted. Figure 6. Mounting with Extension Shaft. The construction of the TH 188 Thermostat makes it virtually maintenance-free. But like any pneumatic thermostat, it should be checked for calibration at least once each year (usually just before the heating season). Preventive Maintenance Table 3. Troubleshooting.
Technical Instructions Document Number 155-064P25 February 3, 2022 TH 188 Unit Mounted Thermostat Figure 7. See Tables 4 and 5. Table 4. Parts List (See Figures 7 and 8).
TH 188 Unit Mounted Thermostat Technical Instructions Document Number 155-064P25 February 3, 2022 Figure 8. See Tables 4 and 5. Table 5. Parts List (See Figures 7 and 8).
Technical Instructions Document Number 155-064P25 February 3, 2022 TH 188 Unit Mounted Thermostat Dimensions Dimensions in Inches (Millimeters) HC and RA Thermostats DA Thermostats Figure 9. Dimensions. Information in this publication is based on current specifications. The company reserves the right to make changes in specifications and models as design improvements are introduced. Powers is a registered trademark of Siemens Industry, Inc.
