Bypass A/C pressure switch OK??

[jefndeb]

Hello,

Our fwd 16k BTU A/C unit intermittently gives a HPF error.
Its a Vector Compact self contained unit.

We have one 230VAC A/C pump that feeds both the fwd 12K BTU AC unit and the 16k Salon AC unit.

Strainer is very clean and there is plenty of water flow coming from both overboard outlets..

When I bypass the High Pressure switch it works fine.

If I understand this correct, if the unit overheats (not sure what i mean by unit) due to low or no water flow, the pressure switch turns off the compressor, via a signal to the main control board, as a means to protect it from failure.

If I have a strong water flow and bypassing/jumping the pressure switch is it safe to assume the switch is intermittent??

thanks for comments...

 

[DavidM]

It could be caused by a bad pressure switch- most likely or it could be caused by scale build up in the condenser that is reducing heat transfer. Fix it, don't bypass it. High pressure is not good for the A/C.

David

 

[jefndeb]

Yes, I agree but there is a very strong outflow of water...from both AC units......

would that not mean that there is enough flow to provide the cooling?.....I thought about doing a flush with a descaler but then I keep saying to myself that there seems to be plenty of flow????...no apparent restrictions.....

 

[Ski in NC]

What is the temperature of the refrigerant coming out of the heat exchanger? You can have good water flow, but internal fouling can make for poor heat transfer. If hot, the switch might be doing its job. If cool, could have a flaky switch.

Tried cleaning the HX with a chemical flush?

 

[jefndeb]

So this morning we attempted to flush the water heat exchanger with high pressure fresh water (water hose) and the water coming out was not dirty at all.....as compared, I also did the same to the fwd AC unit and the boss said that that water was dirty as it exited the drain port...then it cleared..the opposite of what we expected but at least that gives me another clue....the water static temp is 80 and the water exit is 85......

Note--as soon as i press the ON button for the AC unit, the display shows HPF....
seems to me the High Pressure switch it stuck open???

 

[DavidM]

The condenser heat exchanger on an A/C unit is a tube within a tube design. This gives it lots of room for water flow even though there may be 1/8" of scale on the outside of the inner tube- the one the freon flows through. So that scale may not affect water flow significantly, but sure would reduce heat transfer which will cause the high temp indication.

Or it could a bad sensor and there is little scale inside.

So what is cheaper, doing an acid flush or replacing the sensor. But in any case do something. You wouldn't ignore and bypass a high engine temp reading, would you?

David

 

[jefndeb]

Very good point...

Note---as soon as i press the ON button for the AC unit, the display shows a flashing HPF....
seems to me the High Pressure switch it stuck open???

 

[DavidM]

Very good point...

Note---as soon as i press the ON button for the AC unit, the display shows a flashing HPF....
seems to me the High Pressure switch it stuck open???

Ahaaaa! Wish you had said that first. It is almost certainly a bad switch. You might try banging on it first with a screw driver handle. Sometimes that will release it.

It does leave a remaining question- What caused the high pressure switch to trip and then get stuck in the closed position? But replace it and go from there.

David

 

[jefndeb]

Thanks for your help, didnt get much sleep last night tossing and turning over this issue....the PN on the switch is 334255 but that doesnt really matter since I am not able to change it I guess...I think the system has to be re serviced after changing one???

By the way,, while messing with that IR temp tool, i compared the temps between the fwd 12K BTU units compressor housing and this fussy Salon 16K unit..

The outside temp of the fwd (functional) unit was 156F and the temp of the 16K fussy unit was 177F...not sure if that really matters, bigger unit may be a little hotter...

Another note, there is definitely a 10 degree different in the in/out water on the fwd AC pack that is working well.(81 in & 91 out)

 

[Boat]

On many units the switches can be changed without refrigerant leaking.


I would check the switch with a multi meter.

 

[jefndeb]

Yes, the switch was open with the system off or on.