What are causes of a bad High Pressure Switch?

[illuzionb18c1]

I had a hvac tech come out due to no cooling.
He said i need to replace my high pressure switch and that the contactor was bad and needed to be replaced.

1) what are the purposes for each
2) what generally causes them to go bad?

thanks in advance.

 

[imok2]

The bellows usually starts to leak

 

[DRWeig]

High pressure switch is there to save the day when your condenser is really dirty (or other less common reasons), condensing pressure gets too high and it trips the unit.

If not there, the pressure could get high enough to blow the rupture disk and vent the refrigerant charge. Then your low-pressure switch would trip the unit once all the refrigerant is gone.

Imok2 has the most common cause of failure, but the contacts can also go bad from repeated use.

Good on ya,

Goober Dave

 

[DRWeig]

Oh, and the contactor is what starts and stops the compressor motor. Contacts pitted or burned or welded together due to lots of different factors. Could be opening too often under high load or overload. Could be lightning. Could be nasty stuff in the air like sulfur. Lots of possibilities.

They don't die often. I have 20 on the roof of this building, we've had to replace three over the past ten years.

Good on ya,

Goober Dave

 

[macmet]

I'm not sure enough information was given in the original post.

I have experience with high pressure switches on boilers. The previous responses seem to be for other applications.

What is the application in this situation?