[buffalobillpatrick]

No interrupt needed.

I measure 6 temperatures around the HP refrigerant loop:
1. Compressor Out / Condenser In
2. Condenser Out / IHX Hi Side In
3. IHX Hi Side Out / TXV In
4. TXV Out / Evaporator In
5. Evaporator Out / IHX Lo Side In
6. IHX Lo Side Out / Suction Line to Compressor

I also measure 4x water temps. Source In & Out, Load In & Out

Analog 0-5vdc pressure sensor on output pipe from water pump.
Code Steps:
1. With pump off, measure static OFF pressure.
2. turn on pump, wait X seconds, measure ON pressure.
3. The pressure delta between these 2 readings represents the plumbing back-pressure (head) that your water pump & plumbing stabilize at.

1 psi = 2.31 feet of head

This delta pressure won't vary unless pump stops working or a blockage condition.

My code, which I don't have access to on Holiday road trip, verifies that the pressure delta stays +- 10% for each water pump.

This is a Go/Nogo test, actual water flow is unknown, so COP can't be determined.