AC Controls

When applied to system with air cooled condensers, what is the lowest outside ambient temperature that balanced-port valves can typically work without head pressure control?

35 degrees F

What are the parts of a distributor?

A nozzle, conical divider, and multiple holes around the divider cone.

Refrigerant leaves the metering device:

As a saturated mixture of liquid and vapor.

Where is the suction line temperature read when adjusting a TEV?

As close as possible to the TEV bulb.

Which of the following is a rarely used metering device that can be used in applications where the load is constant and an operator is present to make manual adjustments?

Automatic expansion valves.

The operation of a thermostatic expansion valve can best be described as:

Bulb pressure = evaporator pressure + spring pressure

One operating advantage of fixed restriction metering devices over expansion valves is:

Can be used with low starting torque compressor motors.

Technicians should be careful when brazing lines to the evaporator coils that have pre-installed thermostatic expansion valves because the heat from brazing the lines:

Can overheat the TEV bulb and destroy the valve.

What is the advantage of balanced port TEVs?

Can retain good control over a wider range of operating conditions.

Two types of fixed metering devices are:

Capillary tubes and orifices.

When the heat load on the evaporator increases, the automatic expansion valve:

Closes to keep the pressure form increasing.

Besides distributing the refrigerant evenly, a refrigerant distributor also:

Creates a pressure drop across the distributor.

The system capacity of an air conditioner with a fixed metering device decreases or increases when the indoor wet bulb temperature rises?

Decreases.

As refrigerant passes through the metering device, it:

Drops in pressure and temperature.

Internally equalized thermostatic expansion valves measure the ___________ _____________ through a passageway inside the vale.

Evaporator Pressure.

The two general categories of metering devices are?

Fixed and modulating.

A system with a loose TEV sensing bulb would most likely

Have a low superheat.

Which metering device used on flooded evaporators opens when more refrigerant condenses, enabling the refrigerant flow into the evaporator?

High side float.

An overfeeding metering device can cause?

High suction pressure Low superheat Low subcooling

In an air conditioner with a fixed metering device, a decrease in the outdoor ambient causes:

Increased system superheat.

A bi-flow expansion valve:

Is designed to allow refrigerant flow in both directions.

The most common application of the high side float controls is:

Large chillers.

Which type of metering device used on flooded evaporators opens to admit more liquid refrigerant into the evaporator when the liquid level in the evaporator drops?

Low side float.

Which of the following problems can be caused by restrictions in the capillary tubes?

Low suction pressure.

Which type of metering device is able to respond to changes in system operations?

Modulating metering device.

Automatic expansion valves are similar in operating concept to:

Pressure regulators.

Valves that open and close rapidly under the control of electronic circuits are:

Pulse modulated valves.

A device used to evenly distribute mixtures of liquid and vapor refrigerant leaving the TEV to multiple evaporator circuits is called a:

Refrigerant distributor.

Valves that use motors that move in tiny increments are:

Stepper motor valves.

Thermostatic expansion valves are designed to maintain constant:

Superheat.

Thermostatic expansion valves respond to changes in:

Superheat.

Automatic expansion valves are good at maintaining constant:

Temperature.

Why is it dangerous to drill out orifices in metering devices?

The orifices are conical in shape.

Why do standard design thermostatic expansion valves need a minimum pressure drop to operate correctly?

The pressure difference across the pin acts as an opening force.

What two pieces of information are necessary to measure the TEV superheat?

The suction line temperature and pressure.

What senses the line temperature in electronic expansion valves?

Thermistors.

Which of the following metering devices can respond to changes in system conditions?

Thermostatic expansion valve.

What advantages do orifice type metering devices have over capillary tubes?

They are easy to change.

What is the purose of TEV sensing bulbs with a limited, or gas charge?

They produce a maximum operating pressure at high operating superheat.

Which of the following best describes the purpose of a distributor?

To equally distribute refrigerant.

To increase superheat on a thermostatic expansion valve, the adjusting stem should be:

Turned clockwise.

To increase the evaporator pressure, the adjustment on top of an automatic expansion valve should be:

Turned clockwise.

How can moisture in the refrigeration system affect the metering device

Water can freeze up at the metering device, causing a restriction.

Capillary tube metering devices are commonly used today in:

Window units.

A TEV with a dead power element will operatoe:

With a high superheat.

A restricted inlet screen on a TEV can cause

low suction pressure high superheat high subcooling