Archive for January, 2011

HVAC Motor-start relays

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HVAC Motor-start relays

Relays are a necessary part of many control and pilot-light circuits. They are similar in design to contactors, but are generally lighter in construction so they carry smaller currents. Compressors used for household refrigerators, freezers, dehumidifiers, vending machines, and water coolers have the capacitor-start, induction-run type of motor. This type of compressor may have a […]

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HVAC Power Relays

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HVAC Power Relays

One of the control devices is the power relay. It is one of the most often used controls for controlling compressors in refrigeration and air-conditioning. The power relay is also referred to as the main conductor. It is used to apply the main line voltage to the motor circuit. The coil of the relay is […]

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HVAC Water valves

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HVAC Water valves

Manually operated valves are installed on water circuits associated with refrigeration systems—either on cooling towers or in secondary brine circuits. They are installed for convenience in servicing and for flexibility in operating conditions. These valves make it possible to recircuit, bypass, or shut off water flow as desired (see Fig. 11-54). These manually operated shutoff […]

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HVAC Level-Master Control Oil return

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All reciprocating compressors will allow some oil to pass into the discharge line along with the discharge gas. Mechanical oil separators are used extensively. However, they are never completely effective. The untrapped oil passes through the condenser, liquid line, expansion device, and into the evaporator. In a properly designed direct-expansion system, the refrigerant velocity in […]

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HVAC Level-Master Control Installation

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HVAC Level-Master Control Installation

The level-master control is applicable to any system that has been specifically designed for flooded operation. The valve is usually connected to feed into the surge drum above the liquid-level. It can feed into the liquid leg or coil header. The insert bulb can be installed directly in the shell, surge drum, or liquid leg […]

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HVAC Level-Master Control

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HVAC Level-Master Control

The level-master control is a positive liquid-level-control device suitable for application to all flooded evaporators (see Fig. 11-45). The level-master control is a standard thermostatic-expansion valve with a level-master element. The combination provides a simple, economical, and highly effective liquid-level control. The bulb of the conventional thermostatic element has been modified to an insert-type bulb […]

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Level Control Valves Float valve

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Level Control Valves Float valve

A hollow float is sometimes used to control the level of refrigerant (see Fig. 11-43). The float is fastened to a lever arm. The arm is pivoted at a given point and connected to a needle that seats at the valve opening. If there is no liquid in the evaporator, the ball-lever arm rests on […]

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Level Control Valves Capillary tubes

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Level Control Valves Capillary tubes

Capillary tubes are used to control pressure and temperature in a refrigeration unit. They are most commonly used in domestic refrigeration, milk coolers, ice-cream cabinets, and smaller units. Commercial refrigeration units use other devices. The capillary tube consists of a tube with a very small diameter. The length of the tube depends on the size […]

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