Have a Little Giant VCMA-15 condensate drain pump with a pan overflow
switch. The pump has two low voltage connections coming from it which
have been wired together for the 13 years that the installation have
been in the house. These connection I presume are for the high level
switch in the reservoir tank. Why are they wired together. It would
seem to me that both the pan overflow and the high level switches should
be in series with the thermostat circuit. What is the correct wiring
for this pump? What am I missing here?
Looking at the install manual online for a VCMA-15ULS there is only
one switch and it has both NC and NO contacts available. What
you do with either of them is up to the installer depending on the
requirements of the installation. You would use the NO connection
in the thermostat circuit to turn off the furnace and/or AC if the
water level exceeds the max. Where you wire it in the thermostat
circuit can determine if it cuts off just heat or cooling or both.
The NC contacts could be used to wire into an alarm system
if you prefer that instead of the cuttoff approach.
I think you have it backwards. Normally Open means it's open until
the switch is closed. That is the one you might use for an alarm.
The Normally Closed one is one you could put in series with one of the
thermostat wires to prevent system operation when the pan is full and
the pump quit working. You can choose to stop the entir system from
running or to prevent just the compressor from running. Your choice.
Make sure you label it so the next guy isn't outside trying to figure
out why the compressor quit.
I don't think so. Did you read the manual for the pump? It says to
the NO contacts for the thermostat. The switch contacts are NO, but
they must be held closed by the sensor mechanism until the water
On 5/25/2011 8:22 AM, email@example.com wrote:
Do you have any idea why they have been wired together all this time?
By the way I do not use the alarm but want only the high level shut down
to work. Also it would seem to me that I would use the NC switch in
series for it would open on high water and shut the unit down. The pan
overflow switch is separate from the pump and is definitely in series.
Is it possible a well meaning hvac person simply tied these two
together with a wirenut since they were not being used? The absolute
accurate test would be to use a ohm meter on the switch while manually
moving the float.
I don't think so for the high level switch functioned. The diagram
shows a com lead which would enable a series connection but there is not
a third wire. Putting the NC and NO lines in series would shut down the
unit completely. The NO line which is an alarm circuit would appear to
have no effect if tied together with the NC line when there is no
alarmfitted as is the case here. Still puzzled.
You can't have both NC and NO without a third common wire.
The manual shows it having 3 wires, but it's possible the manual
is for a newer version.
As James pointed out a simple test with a VOM meter
or even a battery and light bulb together with moving the float that
works the switch is all that is needed to determine how it works.
If there are only two wires, my guess would be 99% that it's NC
when the water is OK and opens when the water is too high.
That's how you'd want it to work to cut off a furnace, AC, etc.
On 5/26/2011 9:21 AM, firstname.lastname@example.org wrote:
I'll plan on taking it down again today (as want to replace the pump
switch the float operates), ring it out and report. Still puzzling for
the two wires were tied together and when the float switch did not trip
the pump to "on" the high level float cut out the A/C unit as intended.
The actual pump switch is completely separate from the safety switch.
I assume your pump is working and has worked since it was installed.
And that the safety switch is not connected to anything presently in
your installation. So it doesn't really matter what is done with the
wires from the safety switch.
Am I incorrect on any of this? Does the pump work as it should as far
as evacuating the water? If the safety switch is wired into the low
voltage thermostat perhaps you should describe exactly what wires are
connected to what as it relates to the safety switch.
It makes sense that the pump switch (on at high water-off at low water)
is completely separate. It has worked since installed. The safety
switch worked when the pump switch failed. The question relates to
rewiring it for there are two thermostat wires, two water overflow wires
in the pan (those to go in series) and two low voltage wires "always
wired together" coming out of the pump unit obviously for the safety
switch. The safety switch should also be in series but a single
connection in series can't be done.
I'm totally lost here too. He says the pump shuts off the AC when
the pump gets too full, as it should. Then there is mention of
being only two low voltage wires emerging from the pump and that
they are tied together. If they are just tied together and not
to anything, then how can the pump water gettting high turn off the
There is also mention of two thermostat wires? This isn't
but we don't have an accurate description of what is there and how
And if it already shuts the AC off when the pump gets too full of
what is the actual problem and/or objective?
Not rocket science here. Take the two screws out, lift the cover, you'll see
the two wires are connected to a micro switch with 3 terminals. Common,
NO-NC. Attach the two wires to the common and NC terminals, then wire those
two leads in series with the other limit switch
The conclusion ... I hope!
First, thanks for all the suggestions, many of which were on the mark.
Took the pump/tank off today (I'm an expert at it), disconnected the low
voltage wires which were hooked together, hooked up the ohm meter and
raised the float ... opened the low voltage circuit (thus when assembled
shutting off the heat pump on high water level in the tank). Concluded
that when installed the HVAC guys did not want to bother with the high
reservoir shut down allowing the pan water level sensor to open the HVAC
circuit. Put everything in series (high water level, pan water sensor
and thermostat) left pump unplugged and when water level rose, it shut
the system down. Cool now.
Perhaps when I first observed the problem the high water level was due
to a dirty check valve in the overhead drain coupled with the power
company securing the system remotely and then faulty pump control
switch. Three things at the same time ... improbable, but I know the
check vave was dirty and the pump control switch was hanging up.
$40 for a new $12 switch on a rush delivery while I cleaned the existing
satisfactorily in WD 40. # hours of labor in positions I should not be in.
Again thanks for the informed thoughts.
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