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

 

[rustybucket]

I third or 4th that unit being clogged. I'd pull the hoses off the unit and circulate it in a tank, personally would go go ahead and acid clean it while I had everything off. I've seen some whacky stuff make it past a sea strainer only to end up clogging something.

 

[madhatter1]

We just had one compressor go bad. Worked perfect until it didn't. Would trip overcurrent heat switch on side of compressor after 1 second, 20 seconds later reset and then do the same thing. Internal short.

Remember anything electric can break on day one or work for many years beyond expected life span. Works one minute and then not the next. So if sudden issue I would look at electrical.

 

[GCSI]

Yes, the first thing on list was to confirm water flow through unit. I have a spare HP switch on hand. Question is, can I change out switch without refrigeration tools?

 

[madhatter1]

How long does it run before it shuts off? A high pressure switch should not trip immediately because it has to build up pressure and then trip. Also you can hear what is resetting by turning off the breaker after it trips, then wait to hear reset "click" to locate what is tripping. Will take same amount of time it takes for unit to come back on with breaker on.

 

[rustybucket]

I would say no on changing the switch without tools. I may be wrong, not familiar with your specific unit but the system would need to be evacuated, hp switch removed (may be brazed in), new hp switch installed, system vacuumed and filled.

If you have not hooked a manifold up to the system no way I would replace the HP switch yet. It may be doing exactly what it's job is, you may indeed have a HP situation.

 

[Pascal]

Recently I had a bad low press switch on one of my chillers. It was replaced in 2 minutes without having to evacuate the system

 

[Reefgeorge]

There is a high temp cutout switch on the side of the compressor but if that switch trips it’s usually because the compressor is starting to lock up. The compressor stops turning and overheats under full power. This produces the opposite of a high pressure fault so this is not likely the issue. If you want to rule that out you use a clamp meter to look at the compressor amp draw just before the unit shuts down. If the compressor is drawing excessive current (somewhere near the locked rotor amperage spec) then it’s seizing and overheating. Also when a compressor overheats and shuts down it takes quite a while for everything to cool down and for the system to restart. While shutdown the evaporator fan still runs. Since you are getting a HP shutdown code I suspect that the evap fan shuts down, further ruling out a compressor shutting down due to overheating.

If you want to confirm a Schraeder valve on the high pressure switch port I would call Cruisair/Dometic tech support with your condensing unit model number and they can confirm.

George

 

[madhatter1]

The high temp lockout is also an overcurrent device. Too much current heats up the element and it trips. Since there is no heat on compressor yet it resets in 15-20 seconds because the element is the only thing hot and cools back off quickly.

 

[GCSI]

And the answer is......

High Temp switch. Existing Schrader Valve, ten minutes all in to complete repair, now working great.
Brett

 

[Boatsb]

High temp or high pressure.

No valve on the temp switch