View Full Version : Low pressure switch (another newbie question!)

15-03-2017, 10:37 AM
Hi everyone

Another newbie question I'm afraid, hopefully someone can help me understand!

The low pressure switch... obviously it's on the low suction side of the compressor, I remember that from my course a few months ago. But, is the switch activated when the pressure is too low or too high?

The engineer in me says if it's saying 'pressure too low in LP side' it must be that there is a blockage in the circuit somewhere. Maybe the expansion valve is stuck (can that happen?) or perhaps the solenoid valve is not activating (it has voltage on it).

However if it is saying the pressure is too high on the LP side I'm lost... actually now I have written this I'm starting to think it must mean the opposite.

Can anyone give me a pointer, please?


15-03-2017, 12:00 PM
The low pressure switch will normally open the circuit in the event of a pressure lower than the set point as it acts as a safety in the event of low pressure.
You are quite right in that it could be a blockage, the solenoid not lifting or good old fashioned lost its gas charge.

16-03-2017, 01:33 PM
Thanks. That's what I thought, but wanted to check.

I'll check the solenoid next time I am there.


16-03-2017, 02:26 PM
LPS is widely used to activate capacity control elements such as HGB and compressor's steps to keep certain procedures from freezing.

When pressure drops below 0C, it closes the contacts.

16-03-2017, 02:58 PM
LPS can use for alt of fonction
Limit for pressure come down from set point
Used for unloading system sometimes
Used for starting system sometimes
Used for starting fan or solinoid valve in blast frizer
So it depend on how we use it in our system and we disign it