LP switch time delay

[hvac wkr]

Help me- I can't figure out how to draw a time delay into a simple safety circuit. High pressure, Low pressure switches. I need the unit to continue running after the low pressure switch opens for a couple seconds. I just can't figure out how to draw it.

[dapper]

*************** TDR
******* |----------O------------------ Neutral
******* |*****|--|/|--|
**Line ---|--HP--|--LP--|--- LOAD

I would just draw something like this.

[Dallas Duster]

Why would you want to keep a compressor running after the low pressure switch opens? What does 3 seconds matter?

[dapper]

This type of time delay (delay-on-break) is generally used to bypass the low pressure switch on compressor start-up when there might be a cold evap or condenser. Not sure why it would run after the LP opens otherwise.

[kiwicontroller]

I would rather find the solution to why the LP is dropping that low on start up in the first place the delay on break relay is mearly a Band-Aid solution check the super heat and LP cut out settings.

[blackbelt3677]

Maybe this is apprenticeship homework!!

[dapper]

Not a Band-Aid solution at all. A very common and necessary solution often provided from the factory for those of us in much colder climates than you guys.

[Chris_Worthington]

Not a Band-Aid solution at all. A very common and necessary solution often provided from the factory for those of us in much colder climates than you guys.

I thought it was common practice regardless of location, as in any pump-down system

[dapper]

Real common in pump-downs but I'm also thinking about heat pumps and water source heat pumps without pump-down.

[Chris_Worthington]

Real common in pump-downs but I'm also thinking about heat pumps and water source heat pumps without pump-down.

Agreed there are many app's where this needed and used often

Was trying to address thegoodlistener and kiwicontroller comments, as in this is common practice and has nothing to do with a band-aid approach

[Dallas Duster]

Agreed there are many app's where this needed and used often

Was trying to address thegoodlistener and kiwicontroller comments, as in this is common practice and has nothing to do with a band-aid approach

The OP doesn`t say whether he is trying to bypass at start-up. So my assumption was why trying to bypass at safety on a normal safety trip out.
I know most manufacturers have an approved low ambient start kit for this purpose and more safisticated controls should have this built in.

[Chris_Worthington]

Who said anything about start-up?

I thought a normal situation where this this would be used i.e. Pump down would occur at the end of a cycle

There are many app's where timing out a safety is called for, the facts, not a band-aid

[jayhawker]

http://www.icmcontrols.com/products/....php?cat_pk=21

I have used with good luck