Fan Coil Unit Schematic Diagram Interpretation (Pics)

2BobSparky · Jun 28, 2012

Using the diagram it is straight forward enough to see the water level sensor cable in the top left of the printed circuit board, which then runs into the top of the sensor, which can be seen in the last picture.

How does the flood switch work though and why can't I see any evidence of it on the PCB?, marked cables 7 and 8 on the drawing.

The switch opens in "alarm", but physically what is going on here? Where are the cables shown in the drawing?

Strima · Jun 28, 2012

Looking at the PCB there's no cables connected for the alarm. Circled in red.

Is there an alarm circuit?

2BobSparky · Jun 28, 2012

Those are the supply terminals (Line and Neutral) for the PCB though, which were disconnected in order for the PCB to removed from it's housing to be photographed.

The L and N are looped out of the incoming L and N terminals, which come from a switched spur, which feeds the motor as well.

it seems to me as though the alarm circuit doesn't even exist, the drawing shows the alarm from the PCB, but looking at the physical PCB there is no evidence of it.

spark 68 · Jun 28, 2012

This might be the pins here, this probablbly say condensate alarm or someting, I can only se 'sate.

Check to see if the above pins go to the relay contacts via the PCB tracks.

Strima · Jun 28, 2012

My bad, tired eyes, too much looking at three phase motor diagrams. I think I need a pint as just had another look and I can now see the layout.

snowhead · Jun 28, 2012

Probably an option when the unit was built and this unit didn't have it.

I've sen many of these F.C.U's mainly IMI and never seen the alarm cicuit used even if it when the pcb had the connections for it.

The best way to warn of it's immenent failure is to let the condensate overflow thro' the ceiling.
People react to water better than to an alarm.

2BobSparky · Jun 28, 2012

Okay, thanks for the replies and yes that very well might be the alarm cables, highlighted in the reply above. In fact, it definitely is, my memory has just been jogged, and those cables went straight to empty terminals on the same strip that the motor speed cables are connected together.

How does the alarm work then hypothetically, because from the diagram is doesn't make a whole lot of sense. The contacts open, but what are those contacts opening exactly? It just doesn't seem clear.

Marvo · Jun 28, 2012

I would guess it's just a potential free contact that can be used to trigger a remote alarm. There would need to be another PCB or alarm module as the contact is normally closed and opens on alarm. This is a failsafe configuration so if the alarm circuit becomes open circuit due to damage it will trigger.

snowhead · Jun 28, 2012

It's failsafe and being open on alarm stops anyone connecting a lamp directly to the contact and overloading it, you'd have to use a relay with a almp.
If it was used as a signal to a BMS system it wouldn't matter whether it's open or closed on alarm it could be set as an alarm input either way.

2BobSparky · Jun 28, 2012

One more question, looking at the schematic for the motor, why does it only show the incoming Neutral, but no live like it does for the L and N incoming on the PCB schematic?

Marvo · Jun 28, 2012

It shows three options for the live....depending what speed is required

spark 68 · Jun 28, 2012

2BobSparky said:
One more question, looking at the schematic for the motor, why does it only show the incoming Neutral, but no live like it does for the L and N incoming on the PCB schematic?

It does, sort of, marked High, Med, Low, these will be Switched lives, or they could be PWM lives.

2BobSparky · Jun 28, 2012

That makes perfect sense, but I could have sworn there was separate L,N+E coming from the switched spur, which feeds the whole setup, including the motor, the speed wires not included.

I need to go back and take another look.

2BobSparky · Jun 28, 2012

snowhead said:
It's failsafe and being open on alarm stops anyone connecting a lamp directly to the contact and overloading it, you'd have to use a relay with a almp.
If it was used as a signal to a BMS system it wouldn't matter whether it's open or closed on alarm it could be set as an alarm input either way.

What do you mean by connecting a lamp directly to the contact and overloading it? If the FCU is in a ceiling space what good would a lamp do as an alarm signal? Some sort of sounder makes more sense. It's all hypotehtical of course, because the alarm isn't even connected.

I vaguely get what you're saying about a BMS connection option, as then it could be monitored remotely via a laptop or such.

Marvo · Jun 28, 2012

The motor would probably be supplied either via a 3 position speed selector switch or via a PCB that selects the speed required.

Fan Coil Unit Schematic Diagram Interpretation (Pics)

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