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Old 06-11-2011, 01:15 PM   #16
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PTAC On-Off is in the Breaker Box...


Thank you again. I am gradually getting a clearer picture of this. I will peer into the other two units next week.

Here is a photo of the upper part of the control box. It shows the rotary switch and the relay, and how they are mounted in relation to each other. From the professionalism of the wiring and the quick disconnects, I would guess that this is how it was manufactured, with the relay in place.

I was thinking there must be some way to reverse the logic of the thermostat. In summer, 72 degrees "means" to the system that you want it to shut off the cooling when you get the temperature down to less than 72. In winter, 72 degrees means that you want the unit to quit heating when it gets above 72. In other words, in late September the instruction goes from "no more than 72" to "no less than 72".

In some systems there is a switch to get from heating to cooling. In the Fan Coil unit, there is a sensor on the water pipe. When it detects heat, the system "knows" its winter.

I was wondering if the relay reacts to this seasonal changeover, as for example by shifting from normally open to normally closed.

Alternatively, found some discussion here of motor speed control by a rotary switch and a relay. The switch selects a winding (HI, Normal, LO). The relay is on-off.

http://www.askmehelpdesk.com/advice/t-381692.html

John
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Last edited by John Harris; 06-12-2011 at 06:11 PM.
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Old 06-11-2011, 11:24 PM   #17
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PTAC On-Off is in the Breaker Box...


unclip that sensor an see what the temperature stamped on it is could be telling unit there is chilled water or hot water present and that flips the stat action.sat the stat is at that 12oclock position we'll call it 70F...to close on drop of room temp winter and close on room temp rise in summer.how about a model number of any of the 3 yes that factory wiring and mounting...i'll check back tomorrow...any chance of a pix of the schematic
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Old 06-12-2011, 06:17 AM   #18
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PTAC On-Off is in the Breaker Box...


Good chance that both the thermostat and klixon have welded contacts. Blower motor looks relatively new. So the old one may have shorted out and welded the contacts of the above mentioned controls.
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Old 06-12-2011, 12:57 PM   #19
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PTAC On-Off is in the Breaker Box...


Makes sense.

Maybe the entire control system has been by-passed.

Here are two photos. One shows 4 color coded speed control wires at the (probably replaced) motor. The other photo shows these color coded wires emerging from the umbelical at the back center of the junction box.

Maybe whoever installed the motor ran 115V straight through to the "HI" wire of the motor (typically color coded as Red), and completely bypassed everything else in the system.

This would explain why the speed control rotary switch has no effect. The motor runs full tilt even when the rotary switch is set to OFF.

In the event the control box, which contains the rotary switch speed selector, the relay and the themostat, is now just a parts museum.

I would guess it was the building supervisor at the time, probably many years ago, who might have improvised this type of "straight through" solution.

What do you think? Is it possible to guess the motor circuit by looking at the wire nut connections?

Thank you for your insights,

John
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PTAC On-Off is in the Breaker Box...-junction-box.jpg   PTAC On-Off is in the Breaker Box...-motor-color-coded-wires.jpg  

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Old 06-12-2011, 01:20 PM   #20
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PTAC On-Off is in the Breaker Box...


Look for the wiring diagram. It will help you trace out the wires. Shouldn't be that hard to follow, and then fix.
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Old 06-12-2011, 01:37 PM   #21
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PTAC On-Off is in the Breaker Box...


You can put a commercial light switch on that 1900 box, effectively breaking the power to and from your unit. Or you can add one wherever you want as long as you know which wire is the hot and yes, it is wired hot which is why you have to use the breaker. Most ptacs in hotels have a switch mounted under them.
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Old 06-12-2011, 01:47 PM   #22
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PTAC On-Off is in the Breaker Box...




granted they make them steel finish but this is the size for your electrical 1900 junction box.
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Old 06-12-2011, 08:15 PM   #23
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PTAC On-Off is in the Breaker Box...


the white is the neutral and the other 3 are the speed....the selector feeds 115v to the speed wires as you turn it how about a model number
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Old 06-12-2011, 08:46 PM   #24
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PTAC On-Off is in the Breaker Box...


The model is a York/Borg Warner FC4V. The "FC" probably stands for Fan Coil. Looked for a schematic, but none surfaced on the internet. I can probably sketch one, or at least a block diagram, when I get back next week.

It appears the wiring has been hacked at the junction box. Right now, the wiring diagram would show 115 VAC line current going straight though to the red (high speed coil) on the motor.

Best, John
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Old 06-17-2011, 09:32 AM   #25
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PTAC On-Off is in the Breaker Box...


Here is the wiring diagram.

The wiring of the real unit has been changed in a few details. It looks like the Klixon wiring has been modified, and there seems to be a jumper from one side of the dual thermostat switch to the other. The relay, which probably ought to be NO or NC, is neither. I isolated the contacts and I read 5000 ohms across them. Neither open nor closed.

I can provide more detail on the problem spots but at the moment I am just trying to figure out how the manufacturer intended for the system to work.

For example, the thermostat. It is a dual line-voltage thermostat with a capillary bulb. In effect it has two switch "channels," and they are labeled on the unit as "1" and "2". One is heating and one is cooling.

The diagram implies that an SPDT Klixon thermal switch "decides" which channel, 1 or 2, should be active.

My basic question is, which channel number is heat, 1 or 2? Put another way which channel is cool, 1 or 2?

Thank you for your insights,

John
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Old 06-17-2011, 12:03 PM   #26
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PTAC On-Off is in the Breaker Box...


Here is a redrawn version of the schematic with some wiring detail filled in, such as the rotary switch positions and the coil of the relay.

Inside the thermostat "channels" are two thermal switches, one each, one NC and one NO. These have not been drawn.

It appears that even when the fan speed control is set to OFF, the relay can (nevertheless) turn the fan on at its HIGH speed winding, if the thermostat calls for this with a thermal switch closure on Channel 2.

Still not quite clear to me what the 1 and 2 mean, exactly, at the thermostat. It seems to be a standard or convention, though, because the numbers are big and embossed on the unit.

John
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Old 06-17-2011, 12:29 PM   #27
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PTAC On-Off is in the Breaker Box...


the klixon contols the 115Vvoltage (1) to the thermostats (R)s depending on the pipe water temp thats what swings that (6-11) going to the stat.noww the stat inturn with its dial set and the bulb sensing air return swings the 115V to the fan selector or the relay to control fan LO heat or HI cool speeds...4 and 5 are the closure relay contacts for LO fan ... 1 and 3 are the coil in the relay

Last edited by biggles; 06-17-2011 at 12:33 PM.
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Old 06-17-2011, 01:02 PM   #28
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PTAC On-Off is in the Breaker Box...


Is the relay is for the heating cycle only? Still not clear to me which side of the dual thermostat (1 or 2, upper or lower) is for Cooling and which is for Heating.

Seems to me from the diagram that maybe the relay closure energizes the Red, or HI line of the motor? A puzzle, this thing. Maybe I have misunderstood the rotary switch. The three lines for HI, MED and LO are each assigned to a switch position. The only one left for the relay is the OFF position.

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Old 06-17-2011, 02:44 PM   #29
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PTAC On-Off is in the Breaker Box...


1 is the cooling side of the stat because it feeds 115V to the selector switch as shown then you see 2 side of it and the relay the fan selector isn't powered in the heating mode and this all thru what the klixon is sensing and the 1-11 or 1-6 to feed 115V to the stat at those Rs..hope somebody else going to kick in with a sequence for you,one thing for certain nomatter what the stat is set for the klixon on the pipe controls the swing for the season feeding 115Vs as shown that relay is dedicated for the fan cycle with one speed only away from the selector
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Old 06-17-2011, 05:45 PM   #30
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PTAC On-Off is in the Breaker Box...


There is on my unit a jumper wire that crosses the thermostat from the heating side to the cooling side. I drew it into the schematic with a curved line to draw attention to it.

I first thought the jumper was part of the hack job, but now I think maybe it is part of the manufactured product. It looks manufactured.

It seems to me that for the relay to close, ever, there has to be power on the wiper of the rotary switch. With the jumper, the wiper has power summer and winter. The jumper does not seem to otherwise affect the operation of the heating channel.

John
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