Yet another Cruisair question

[GCSI]

Unit short cycles for seconds, then quits; repeats a few times after short period, then I Hi PS code on SMX Display. (CruisAir FN7C-P)
- confirmed water flow through unit (unit quits after few seconds, not typical of no/low water flow).
- tried tapping on reversing valve.
- other units on that cooling pump manifold are fine

Any thoughts on low lying fruit?

Brett

[Westfield 11]

Have you cleaned the dust filter on the air handler recently?

[Finalee]

A bad high Pressure switch will do that. Gauges will help you figure it out.

[motoryacht lover]

I had a similar issue with one unit and I took the chance and made a bypass with a short piece of wire with the proper connections. That proved the the HP switch was bad. Once again you are taking away a safety feature so try at your own risk.

[Reefgeorge]

Be certain that the unit in question has good water flow through it, not just the output of the manifold serving all of the units on that pump. Lack of cooling through the heat exchanger would cause high pressure but probably not high enough to trip the HP switch that fast.

There can be a restriction in the refrigerant circuit causing actual high pressure. Do you here the reversing valve cycle at the beginning of start up? Is there a filter dryer anywhere in the high pressure liquid line? If there is a restriction then running it in heat mode and then back to cool will sometimes open up the restriction at least long enough to convince you that this is the problem.

It can be a faulty HP switch or the associated wiring and connectors. As mentioned, The definitive test is to have someone qualified watch the pressures with a set of gauges as this is happening. If there is no actual high pressure in the liquid line then its most likely the switch.

A safer way to evaluate the switch without gauges is to swap with a know good transducer and see if the problem follows that switch.


George

[GCSI]

I have a spare switch on board. Can I do this without evacuating the system? If se, any “tricks” that a novice should know?

It looks like the switch screws into a Schrader type valve that should self seal....

Brett

[Reefgeorge]

I am not familiar with every model of Cruisair condensing units but it should screw into a schrader valve. Just assume its going to leak and protect the port and you as you unscrew the switch to be safe.

George

[Pascal]

Have you actually pulled the discharge hose in a bucket and confirmed flow to that unit? I have had the same issue over the years where only one condenser would short cycle and it turned out to be a shell blocking flow. Others on the same pump where fine.

[jmooney]

I agree with Pascal. I had the same thing happen. But, I think the unit is low on freon.

[Reefgeorge]

Low refrigerant will cause a shutdown with a low pressure alarm not high pressure as the OP is experiencing.

George