For this set up, I would do it like this:

Setpoint reached:
1.Close liquid supply
2.GPLX remains open
3.fans continue running

Defrost:
1.close liquid supply
2.wait 2-3 minutes
3.open hotgas
4.wait 5 seconds
5. close GPLX


Start cooling after defrost:
1. open GPLX
2. wait 2-3 minutes
3. open liquid

The GPLX is a 2 stage valve so it won't open fully until the differential pressure across the valve is low enough for the hotgas pressure to lift the main valve seat.
This is also why you don't open the liquid valve until the GPLX has fully equalized the pressure, if you introduce liquid to soon, the increase in pressure in the cooler will make it take longer to open the GPLX.

On set ups like this we usually have a smaller solenoid valve bypassing the main hotgas valve to increase the pressure a bit before the main hotgas valve opens.