Specifications

A/C System Components

3-17

TOYOTA Air Conditioning and Climate Control – Course 752

Pressure

Relief

Devices

For safety, every pressurized system must have some sort of pressure-relief

system to reduce excess system pressure before it can become a hazard.

n an A/C system, a

usible plug

as one type of safety device. A fusible

plug is a hollow bolt filled with a soft, low-temperature solder. The plug

then threads into the top of the receiver-drier. If the pressure in the high

side of the system exceeds a predetermined limit (400 psig or 30 bar) or if

the temperature exceeds 220° F (110° C), the solder melts out of the bolt

and the pressurized gas escapes. On current models, a pressure switch

de-energizes the compressor when system pressure becomes excessive.

Possible causes of excessive pressure or temperature:

• Restriction in the high side of the system

• Overheating condenser due to restricted airflow or fan failure

• System overcharged with refrigerant

• Abnormal heat source (e.g. steam cleaner)

After the system is repaired replace the receiver-drier.

On some other vehicles, a pressure relief valve performed the function

of the fuse plug. Threaded into the compressor valve assembly, the relief

valve opened when

the system pressure exceeded 400 psig (30 bar). It

only stayed open until the

pressure fell below a lower limit. That avoided

a total loss of refrigerant.

A/C systems using a relief valve may also have

a pressure switch

to de-energize the compressor as described above.

Although effective, this type of safety device vents refrigerant to the

atmosphere, which is no longer allowable.

The pressure relief valve was not designed to reseal after it opened.

If you

suspect the valve has opened, replace it after recovering the remaining

refrigerant in the system and repairing the cause of the malfunction.

Note:

Exit

Bookmarks

Home