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Air Conditioning

Pressure Switches

Air Conditioning

Pressure Switches

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High Pressure switchHigh Pressure switch

• Used to protect the compressor

• When condensing temp gets too high

• Reads High Side Pressure

• Located in condensing unit

• Can be wired line duty or control voltage

• Used to protect the compressor

• When condensing temp gets too high

• Reads High Side Pressure

• Located in condensing unit

• Can be wired line duty or control voltage

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High Pressure switch cont…High Pressure switch cont…

• Opens on rise in pressure/ closes on drop

• Adjustable type-normally set to open at 350 psi with a 75 differential

• Non-adjustable type-are pre-set to pressures-re-set button must be pushed

• Opens on rise in pressure/ closes on drop

• Adjustable type-normally set to open at 350 psi with a 75 differential

• Non-adjustable type-are pre-set to pressures-re-set button must be pushed

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Types of High pressure switchesTypes of High pressure switches

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Types of High pressure switchesTypes of High pressure switches

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Types of High pressure switchesTypes of High pressure switches

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Types of High pressure switchesTypes of High pressure switches

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Low pressure SwitchLow pressure Switch

• Safety switch• Opens on pressure drop/ Closes

on pressure rise • Condensing unit de-energized• Indoor Blower motor remains

running

• Safety switch• Opens on pressure drop/ Closes

on pressure rise • Condensing unit de-energized• Indoor Blower motor remains

running

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Low pressure Switch cont…Low pressure Switch cont…

• opens at about 55 psig (R-22)• located in condensing unit• wired line duty or control voltage

• opens at about 55 psig (R-22)• located in condensing unit• wired line duty or control voltage

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Low pressure Switch cont…Low pressure Switch cont…

Opens due to: • Restricted air flow- registers,

return grills, loose belt, dirty evaporator

• Low refrigerant charge- leaks

Opens due to: • Restricted air flow- registers,

return grills, loose belt, dirty evaporator

• Low refrigerant charge- leaks

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Types of Low Pressure switchesTypes of Low Pressure switches

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Types of Low Pressure switchesTypes of Low Pressure switches

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Types of Low Pressure switchesTypes of Low Pressure switches

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Low Ambient ControlLow Ambient Control

• Cycles condenser fan On and Off

• Runs system at Design pressure -when outside ambient temp.

are low-found in some residential

units-usually found in commercial

systems

• Cycles condenser fan On and Off

• Runs system at Design pressure -when outside ambient temp.

are low-found in some residential

units-usually found in commercial

systems

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Low Ambient Control cont…Low Ambient Control cont…

• Wired in line side only-best to wire after “C” on

condenser fan

• Closes on pressure rise (250 psig)• Opens on pressure drop (200 psig)

-50 psig differential

• Wired in line side only-best to wire after “C” on

condenser fan

• Closes on pressure rise (250 psig)• Opens on pressure drop (200 psig)

-50 psig differential

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Low Ambient Control cont…Low Ambient Control cont…

There are different types of LAC’s:

•pressure sensing•condenser discharge air

sensing•liquid line sensor

There are different types of LAC’s:

•pressure sensing•condenser discharge air

sensing•liquid line sensor

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Low Ambient Control cont…Low Ambient Control cont…

Function LAC provides:

•High condensing pressure•Good refrigerant flow•Keeping low side temp above

freezing

Function LAC provides:

•High condensing pressure•Good refrigerant flow•Keeping low side temp above

freezing

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Sail SwitchSail Switch

• Mechanical switch that proves air flow• Located in ductwork• Switch is open when no airflow is

present• Will close when fan comes on• Prevents freezing of evaporator coil

due if indoor airflow is not established.

• Wired in “Y” circuit

• Mechanical switch that proves air flow• Located in ductwork• Switch is open when no airflow is

present• Will close when fan comes on• Prevents freezing of evaporator coil

due if indoor airflow is not established.

• Wired in “Y” circuit

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