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Siemens 188 Unit Mounted Thermostats

Unit Mounted Thermostats

The 188 Unit Mounted Thermostat is a gradual acting thermostat with a remote bulb operating on the forcebalance principle, using pneumatic feedback to obtain linearity and maintain selected room temperature by positioning pneumatic devices to control heating or cooling.

• Liquid-filled thermal system temperature sensing element
• Durable die-cast metal case with rugged setpoint knob
• Adjustable sensitivity
• Universal mounting bracket for easy installation
• Integral adjustable limit stops
• Available as: – Direct Acting only (Heating) – Reverse Acting only (Cooling) – Heat or Cool depending on supply air pressure

Select a link under the "item" tab below to order.

Cat #TypeControl ActionChangeover PressureAverage Air Usage
188-0031Single SetpointDirect Acting / 25 psi (172 kPa)-40 scim (11 ml/s)
188-0024Single SetpointReverse Acting (Cooling) 18 psi-20 scim (5 ml/s)
188-0030Heat/CoolDirect Acting / Reverse Acting (Cooling) 18 psi (124 kPa)-40 scim (11 ml/s)
188-0033Heat/CoolRetroline Direct Acting/Reverse Acting 18 psi (124 kPa) / 13 psi (90 kPa). Retroline replacement for Honeywell LP916BXXXX.15 psi (103 kPa)40 scim (11 ml/s)
188-0034Heat/CoolRetroline Direct Acting/Reverse Acting 20 psi (138 kPa) / 15 psi (103 kPa). Retroline replacement for Johnson Controls T-3300-2.17 psi (117 kPa)40 scim (11 ml/s)
Control Action Heating/Cooling, Direct and Reverse;
Direct only; Reverse only
Operating Range 60 to 85°F (15.5 to 29.4°C)
Operating Pressure 30 psi (207 kPa) max.
Adjustment Sensitivity 1 to 5.25 psi/°F (12 to 65 kPa/°C)
Factory Sensitivity Setting 2.25 psi/°F (28 kPa/°C)
Temperature Response 0.2°F (0.1°C)
Maximum Ambient Temperature
Case 135°F (57.2°C)
Bulb 231°F (111°C)
Scale Graduations 1°F (0.55°C)
Nominal Air Supply Pressure
Direct or Reverse Acting 25 psi (172 kPa)
Heating/Cooling 25 psi (172 kPa)/18 psi (124 kPa)
Average Air Usage
20 scim Restrictor 25 scim (6.8 ml/s)
40 scim Restrictor 45 scim (12.2 ml/s)
Air Connections 1/4" (6 mm) Brass barbed for polyethylene tubing
Bulb Size 3/8" Diameter x 3-1/2" L
(9.5 mm Diameter x 89 mm L)
Capillary Length 48" (121.9 cm) approx.
Finish Corrosion-resistant Zinc Chromate
Dimensions (case)
Heating/Cooling, Reverse Acting 3.1" W x 2.4" H x 2.13" D
(100 mm W x 61 mm H x 54 mm D)
Direct Acting 3.1" W x 2.4" H x 1.38" D
(100 mm W x 61 mm H x 35 mm D)
Shipping Weight 3.0 lb. (1.36 kg)

The 188 Unit Mounted Thermostats are designed primarily for use in fan coil induction units and unit ventilators to control the temperature within an occupied space. The thermostat’s temperature range is limited to applications at ambient temperatures.

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