View Full Version : carrier rtu
05-17-2005, 07:46 AM
does anyone know the minimum amperage the CLO on a carrier RTU will lock out at? Has anyone ever use a Wagner 007 and who carries them.I was told this is a resetable tattletail.This may let me know what it lock out on.Every once in a while I get a unit thats locked out and I would like to know why.
05-17-2005, 08:32 AM
Approx. 1.5 amps. If you are going to use tattle tales to troubleshoot these trips, you need to disable the CLO while they are in place.
05-17-2005, 10:50 AM
are you saying it locks out at 1.4 amps.all the safeties are automatic reset,so it's a problem tring to troubleshoot.do you have any info on this Wagner 007.it suppose to be a tattle tail that you can reset.
05-18-2005, 08:57 PM
Footpound, The clo does not lockout on high amp draw.
I know it seems that way looking at the current sensing
loop. I forget exactly the purpose of the current sensing,
Someone here will know. It locks out only if one of the safties in the comp. control circuit opens. You have to
figure out which ones opening. Tattletales wont work in this case. There has been much discussion here on this
subject. try a search on this forum and read some of the
methods used to track down which switch is opening. The
wagner007 wont help much here I dont think. Hope this helps
05-19-2005, 06:51 AM
Thanks AC.Your right,I did find a few past articles on this subject that where very helpful.The CLO locks out the compressor on no amp draw.When I find a Wagner 007 I'm going to experiment with it,I let you know what I find.
05-19-2005, 09:38 AM
Yank the CLO out of there and replace existing safetys with manual reset HP & LP.
05-19-2005, 01:13 PM
You may be right,these CLO,s are a pain in the arse.With manual reset at least you know what you got.
05-19-2005, 01:51 PM
Very often the unit locks out on LP during a cold morning start up, for that you can also add a time delay sw to prevent it. Freeze stats solve a lot of problems too.
05-20-2005, 09:08 PM
Thats right it locks out on no amp draw,You saved me from
tacking down that literature. Thanks
I agree they are a pain I like the idea of replacing it
with manual reset switches. I use man. reset switches to
track down the problem.
I have a couple units now locking out...pressures and temps
are perfectly normal after resetting of course.
These CLO'S have a resistor from 1 (common) to 2(power in
on cool call) Anyone know the purpose of this???
05-21-2005, 08:58 AM
We know, but if we tell ya.........well.....you know.......we have to kill you.
05-21-2005, 12:17 PM
I was told by my local Carrier tech that the loop senses lowamp draw, so it will lock out if low load occurs to prevent freeze up. Not sure how knowlwdgeable he is though. He told me to take the wire that goes through the loop and loop it twice through it. I have done this on 2 systems and have not had anymore lockouts.
05-21-2005, 06:51 PM
It sounds to me that you have an inductive sensor which consists of a wire-wound core and a signal conditioner. The current conductor passes through a magnetically permeable core that magnifies the conductor's magnetic field. When the AC current constantly changes potential from positive to negative and back again, generally at the rate of 60 Hz., the expanding and collapsing magnetic field induces current in the windings. This is the principle that governs all inductive loads such as a relay in the control circuit.
One of the most common applications for induction current sensing is motor monitoring, because current draw is such an excellent indicator of motor condition. I believe the best solution for you problem is to do as ace12 suggests, this should be quite easy to do.
05-21-2005, 08:46 PM
The CLO locks the machine out only by reading 0 amps (not high or low amps). More than likely it is locking out early in the morning hours. Place a delay on break timer across the contacts of the low pressure switch and more than likely that will solve your lockouts.
05-22-2005, 02:22 AM
Simple tattletail, Put a fractional amp fuse accross safeties that you think may be causing the trip. but first check that the safety circuit will blow the fuse.
05-22-2005, 08:47 AM
Snipe, Do you mean a fuse below 1 amp will blow if the switch opens even though the voltage at the switch is
removed that instant??
Have you ever seen resistors on a clo ?
Ace, Your Carrier rep is wrong, Looping the wire through
twice does nothing in this application. It locks out only
if no amps occur on call for cooling...which is kind of
silly, I guess thier trying to protect against single
phasing but only if the sensed leg is lost?
05-22-2005, 10:48 AM
I have had this page for years and cannot remember who gave it to me.
CLO stands for 'Compressor Lockout'. It is one of the most
misunderstood devices on any Carrier equipment. I don't know why,
Itís not difficult, but it is often misunderstood.
It is what it says - a compressor lock out. It is NOT repeat *NOT* an
Over-amperage safety, which many people think it is.
Here's how it works -
Pin 1 is ground. Or 'common, whatever you want to call it.
Pin 2 is incoming +24 Volt from Y1 (or Y2) on a 'run' command from
Pin 3 is outgoing +24 Volt.
Pin X is also outgoing +24 Volt (as described below, inverted from
Pin one is hardwired to common, or ground. It never changes.
Pin 2 is (either before or after, I forget) in series with the high
and low pressure safeties, and the compressor contactor coil.
On a call for cooling (such as Y1 is energized by the thermostat, in
which case we are discussing CLO1, or Y2 is energized, thus CLO2) +24
Volts is applied through the series circuit of:
Transformer supplies +24 V
'R' of the stat
'Y1' of the stat
'13' or 'J1' (I forget) at that stupid little control terminal strip
(Just a junction point)
The economizer relay, if present - (closed = mechanical cooling)
back to 13 or J1 from the economizer (whichever it didn't leave on
Pin 2 of the CLO,
Passed through the CLO to pin 3 of the CLO.
The low-pressure safety
The high-pressure safety
The contactor coil
(And of course back to common after the coil)
(Again, please forgive if I have the sequence wrong, but it doesn't
matter, because it's a series circuit)
In it's 'Normal' position, the CLO will pass the +24 coming in on pin
2 out to pin 3, then to the HP and LP and freeze stat safeties, then to
the compressor contactor.
The little black box on the CLO board is a potential relay. It is
powered by the inductive loop, which you see as that shiny silver loop
that is part of the board, with ONE WIRE ONLY of the compressor power
leads passing through it.
On a call for cooling, the compressor runs. The potential relay is
energized by the current picked up inductively in that metal loop on
the board, and the 24 V control voltage is passed from pin 2 (which
is fed by Y1 AKA 13/J1) to pin 3, then out to the HP and LP and
freeze stat safeties, then to the compressor contactor, which is
energized. The current flowing through the compressor power lead that
goes through the inductive loop sensor energizes the potential relay,
and maintains a contact from pin 2 to pin 3 of the CLO, allowing the
24 V from Y1 to pass through.
Failure mode Operation:
Break this circuit anywhere - HP, LP, whatever. Or, have a compressor
that is not pulling current through the leg that passes the inductive
The CLO now sees a 24 volt potential between pins 1 and 2, but no
current to the compressor on the high voltage side.
The other components on the board look at this (call for cooling, but
the compressor is not pulling any amps), and say 'hey, not good -
we're asking the compressor to run, but it's not running. Let's lock
So, it locks out. The 24 V between 1 and 2 keeps it locked out, until
you reset it either by powering down the unit, or turning the call for
cooling off for a moment. Either way will break the 24 V between 1 &
2, and release the lockout.
In the meantime, pin 3 has energized with 24 V relative to ground.
You will rarely see this pin used. It is so that you can have a 24V
alarm signal. Pin 3 energizes only in the 'failure / lockout' mode.
The CLO is NOT an over-amperage device, and that's simple to prove.
How can you have over amperage protection on a three-phase motor by
sensing only one leg? You canít! What if the leg you're sensing
were the one with no voltage, and thus no current? The other two
legs would be pulling LRA, and you'd never know it! So, the CLO
Obviously CAN NOT BE an over-amperage device.
05-22-2005, 10:11 PM
HVAC Manager, I didnt realize that current loop was used
to energize the pot. relay. Makes sense now why only one
leg is sensed.
Have you ever seen a resistor from term. 1 and 2 ?
05-22-2005, 10:58 PM
the CLO sees if a safety opened while
the compressor was running and locks it out.
How can the CLO sees that the compressor is running??
the current sensing loop
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