Replacing Honeywell T651A tstat for condo fan-coil system


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Old 02-04-17, 09:57 PM
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Replacing Honeywell T651A tstat for condo fan-coil system

Hello everyone, I'm really sorry if this has already been asked and resolved before (I searched here & google . . .)

My condo has a fan-coil heating/cooling system, with building supplied chilled water (in summer or when warm) or an electric heater within the system when cold.

Currently there is a fan control unit and a separate thermostat with Heat/ Cool switch (Honeywell T651A). Line voltage comes into the fan control switch, which then goes to thermostat which (I presume) tells the heating coil to turn on (in Heat setting) when below temp or presumably a valve that feeds in the building supplied chilled water to system (in Cool setting) when above set point. One problem with this setup is that the fan is always on, even when set-point temp is reached.

Talking to neighbors & building maintenance, I was advised to get the Honeywell SuitePro TB6575A1000 thermostat for 2/4 pipe fan coil system, which I did.

I do not know how to connect the 2 (orange) wires coming from the fan motor to the TB6575A unit. I think I got the 1st four connections on this unit (see last pic: L1 hot, L2 neutral, Heat, Cool). The 2 orange wires currently are connected to the red & brown wires (labeled MOTOR) on the fan speed controller. One of those orange wires connected to red MOTOR wire also goes to the thermostat's L1 hot connection.

So, in brief, my question is where do I connect the 2 orange wires coming from fan motor on the new TB6575A thermostat. Also, am I correct in connecting the Heat (red) & Cool (blue) wire from the wall to the Heat and Cool pins on TB6575A?

Thanks in advance, & sorry if my post is too lengthy!

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Old 02-04-17, 11:10 PM
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Welcome to the forums.

There are threads on PTAC thermostats but each unit is unique requiring a different approach.

Your holding what looks like the speed control with the diagram unreadable because it's not facing the camera ??
 
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Old 02-04-17, 11:45 PM
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Thanks PJmax, here's a pic of the diagram on the fan controller, though not sure if it might help much . . .

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Old 02-05-17, 01:51 AM
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That looks like an odd setup.

I have seen many McQuay fan controllers installed at the Chilled water air handler but they usually control the 3 speed setting.

The diagram for the temperature control has numbers but I see no numbers at the 3 terminals used.


I have always removed those controllers and installed a contactor and transformer or a fan center so that I could use low voltage stats.

The stat white is neutral. Red is heat and blue is cool.
The fan control black is L1 and the stat Orange is L1. Are you saying that these wires are connected in front of you? That would make sense but I don't see that picture. I don't see the second orange wire bridged to the temperature control and fan control.
 

Last edited by Houston204; 02-05-17 at 02:12 AM.
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Old 02-05-17, 10:53 AM
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Below is a diagram of the current wiring. (the black circles represent connections)
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There are 6 wires coming out of the wall: black, white, 2 orange, blue red.
The 3 wires connected on the thermostat are to the #3, #5 & #6 terminal based on the layout in 2nd picture of my first post.

So question remains, where to connect the 2 orange wires coming out of the wall (which I'm pretty sure goes to fan motor).
Secondary question/ comment: even though fan switch is a rotary one with infinite positions, based on sound, I think there are only 2 speeds: high, low (& off).
 
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Old 02-05-17, 12:42 PM
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Based on the pic.....
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3= orange = hot (when fan control is on)
5= red = hot valve
6= blue = cold valve



I'm trying to find info on the McQuay fan control. It looks like it takes 120v in on white and black and sends out variable power on red and brown.

Is there any type of wiring diagram on the main unit ?
 
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Old 02-06-17, 03:52 PM
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Yes Pete, you are correct-- there was an error in color code in my diagram
On thermostat (T651A)
#3 is L1 orange wire (looks yellowish in diagram)
#5 is heat RED wire
#6 is cool BLUE wire

The only wiring diagram on the main system relates to wiring in system, not connection to thermostat or fan controller
 
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Old 02-07-17, 06:49 PM
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I haven't seen a McQuay with a dimmer switch. Does your fan control click into Hi and Low or does it act as a dimmer switch would?
 
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Old 02-07-17, 07:09 PM
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I'm pretty sure the dimmer switch doesnt act like a dimmer; just Hi upon being turned on & then Low at other end of the turn (based on the sound volume from system)
 
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Old 02-07-17, 07:32 PM
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I have spent over half my life working in high rises but I have not seen that setup before. It sure looks like a dimmer in your drawn diagram.

I usually see a 3 speed fan switch on the wall next to the stat or on a J-box at the air handler. When I install McQuay chill water fancoils I always install the 3 speed switch at the air handler.

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A dimmer throws a curve into this install.
 
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Old 02-07-17, 08:07 PM
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I don't need the thermostat wiring. I'm trying to determine why there are two orange wires from the fan motor. Right now it looks like you put power on the orange wires and the fan runs. Probably variable speed at one time.

That would be easy enough to do from your new stat. Fixed at one speed.

OR..... the two orange wires are both power back to the blower. One is high and one is low.

Post whatever diagrams you can find. Maybe even the model number of the unit.
 
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Old 02-07-17, 08:17 PM
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Houston: So in the case of the McQuay 3 speed fan switch, in addition to the black & white (power-line) connections, do you have 4 other wires going to the fan or is it 3?

For what its worth, here's a pic of my front plate of fan controller
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Old 02-07-17, 08:31 PM
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Normally a mechanical type speed switch has one power or common in wire and one wire out for each speed.

I'm fairly certain you can wire the blower into your new thermostat but it will not be variable. It will be full speed.

You could still use that Mcquay speed control if you wanted to.
 
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Old 02-07-17, 08:32 PM
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PJ: Whether the 2 orange wires are for Hi or Lo: if Houston's 3-speed switch has 3 wires from the switch, then we'll know mine are Hi/Lo.
If Houston has 4 wires, then I guess one wire is Neutral?

By the way, of the 2 orange wires, only 1 goes to thermostat-- presumably to power the valves from there? That would suggest the other orange should go to neutral
 
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Old 02-07-17, 08:42 PM
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I usually have yellow for power in, Red - low, Blue- medium and black for high speed. There is also a capped brown wire.

( Actually 2 of each because I almost always have twin blowers)
 
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Old 02-07-17, 08:43 PM
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Houstons type switch will not work for you.

On the old Mcquay switch..... as soon as you turn it on....
brown is 120vac
red is variable neutral.

The orange wire to your old stat went to brown.

Here's how you can wire your system.
Keep the orange wires on the Mcquay control.
Connect the white to L2/white/neutral
Connect the black to BROWN/high speed fan

The Mcquay control must be left on and high speed must be selected on the new stat.

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If you don't care about variable speed..... connect one orange wire to brown on new stat and the other orange wire to L2/white/neutral.
 
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Old 02-08-17, 12:06 AM
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Thanks PJ, I'm getting towards the same conclusion as you.

I definitely don't want to keep the old McQuay fan controller AND a new thermostat. One of the reasons for the change is so that fan goes off automatically upon reaching set point. I'd gladly give up the current 2-speed fan option.

So are the 2 orange wires from the wall interchangeable-- ie if the 2 orange wires from wall/ fan motor are to connect to A and B, does it matter if its B & A, instead?

And I have another lingering doubt:
Since my current fan speed options are Hi and Low, and the wires coming out of the McQuay fan controller (FC) are Brown & Red (connected to 2 different orange wires from wall), could it be that the respective orange wires should go to the brown & red on new stat?
If this was the case, the part that is confounding would be that the orange wire connected to the brown wire on McQuay FC also goes to the old stat's L1

Thanks again, I think we're getting close
 
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Old 02-08-17, 10:28 AM
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You mentioned diagrams of internal wiring.... was that a no go ?

The Mcquay unit appears to be a variable speed motor controller. That would mean you only have a single speed motor.

On the new stat.... only one speed terminal is live at a time so connecting to two of them will yield no activity at all.

If you connect the Mcquay to the brown wire.... it will follow the programming of the thermostat and turn off with the thermostat.
 
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Old 02-16-17, 03:09 PM
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Thanks PJ & Houston for your help!
I believe new stat is working (at least so far, no sparks, & the TB6575A is working, displaying ambient temp). I will shortly confirm that heat/cold is indeed working & system is shutting off on reaching set points.
For the record, and future visitors with a similar problem, these are the connections made to the new stat (TB6575A1000) . . .

Wall wires Stat connections
Black L1 Hot
White L2 Neutral
Orange(2 red) Brown Hi Fan
Orange(2 brwn) to White & L2 Neutral
Red Heat
Blue Cool

I'm not sure if the orange wires coming from the wall are polarity sensitive; for sake of consistency, the orange going to the red wire (on old McQuay) is connected to High Fan on new stat, and orange wire going to brown wire (on McQuay) is connected to white wire (from wall) & L2 Neutral on new stat.

Thanks again for your help & patience!
 
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Old 02-16-17, 09:24 PM
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Right.... those are the connections I gave you. Everything will work fine but you'll only have one fan speed.

I don't know why two orange wires were run. It should have been a white and a color.
Technically there is no polarity on the motor so connecting it either way is ok.
 
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Old 02-19-17, 02:02 PM
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Minor correction/ update:

I had to connect the orange wire from the wall that originally went to the red wire on McQuay fan controller to the Red (Low Fan) wire on the new thermostat (TB6575A1000).
The reason is that this stat when set up for only 1-speed fan needs that connection. Now the fan automatically shuts down along with heater (or AC) when temperature set-point is reached.

Once again, thanks for your help PJMax & Houston204!
 
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Old 02-19-17, 02:07 PM
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Interesting..... I would have guessed the high speed would be the default for single speed operation. Thanks for the update.
 
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Old 02-20-17, 02:00 PM
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Hi Pete, before tossing out the old McQuay fan controller I checked the voltage output on the red wire (which went to the fan motor); it varied between ~4VAC to 0VAC between the high & low speed settings. Is it true all current/modern HVAC systems now output signals on 3 separate lines for 3-speed control?
Before I started off on this project, I tried finding a wifi capable thermostat for my fan-coil system, but soon gave up & settled for the honeywell tb6575a. Do you know of any wifi capable stats for fan-coil systems (that run on line-voltage), or is that going to be a bit of a kluge with transformers, etc?
 
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Old 02-20-17, 02:11 PM
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There isn't one that I know off.

There are three fan speed outputs on those stats but they are all the same voltage.

It's pretty hard to check the output of those fan speed controllers. They rely on the current from the fan motor to vary the speed. That McQuay unit was probably fully variable at one time.

Technically.... you could buy three fan speed controllers and attach one to each fan speed on the thermostat. You could fine tune each control.

You could leave full power as high and add one in for a single lower speed.
 
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Old 05-29-17, 07:52 PM
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Replace Honeywell T6069D with a TB6575A1000 Thermostat

Apologies for jumping in on another's thread. Just registered, first post.
Honeywell told us the TB6575A is a proper replacement for the T6069D, saying "To replace your current thermostat you would need to run a neutral wire or use one of the fan wires as a neutral as a fan speed."
The Super tried to do a (colour) wire for wire replacement except for replacing the old violet with the new white on, as seen in r2d2c3p0's post of 02-16-17 05:09 PM and the new one didn't work.

What should we look at?
 
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Old 05-29-17, 08:28 PM
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Welcome to the forums.

You need to post what color was on which terminal of the old stat.
Do you have the same McQuay unit as the OP ?

These fan coil units are not easy to wire and harder for us not being there.
They very rarely follow a wiring diagram.
 
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Old 05-30-17, 06:16 PM
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Thanks, Pete,

This is the existing diagram shows the current 7 colours leads connected via twist-ons.

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The Aquastat (Yellow, White, Orange pipe clip on unit) is clearly identified but then points to the "Valve".

The TB6575A1000 also has 7 leads, but instead of the violet one a white one.
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Old 05-30-17, 07:42 PM
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The Aquastat (Yellow, White, Orange pipe clip on unit) is clearly identified but then points to the "Valve".
I don't see white. Did you mean violet ?

That T6069D diagram is a supplied diagram...... not necessarily your exact setup... correct ?
In that diagram is no provision for electric heat.
 

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Old 05-31-17, 07:57 AM
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No, those are the leads on an uninstalled Aquastat.

I'll get back (much) later with the actual paring of the wire colours.
 
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Old 06-01-17, 03:33 PM
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All wire colours of the T6069 are wire nut connected to the same colours in the box behind the thermostat.

The Aquastat, pipe mounted sensor, does have a Ywellow , Orange and White wire.
This white wire and another White one, connected to the solenoid valve, is wire nut connected with the Violet one from the thermostat.

When we contacted Honeywell about a digital replacement, they said that the TB6575A1000 was compatible and:
"To replace your current thermostat you would need to run a neutral wire or use one of the fan wires as a neutral instead of a fan speed."
 
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Old 06-01-17, 03:44 PM
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The two thermostat diagrams do not depict the same functions. I see no connection for your electric heat. I can't really tell you how to interchange the stats without knowing all the particulars.

I can address the neutral part. Your new stat needs a neutral to run the electronics.

You have a....... brown - high fan, blue - medium fan and red - low fan.

Pick the speed you want to give up. Disconnect that color at the FCU and move it to neutral.
At the stat.... THAT color will become the neutral.
 
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Old 06-01-17, 04:29 PM
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The two thermostat diagrams do not depict the same functions. I see no connection for your electric heat.
This is for a fan coil unit, a hydronic system, there is no electric heat.

During the cooling season cold water runs through the pipe and when the thermostat calls for cooling, the valve to the heat exchanger is opened.
The same is happening during the heating season, except it is hot water that is sent through the heat exchanger.
 
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Old 06-01-17, 07:19 PM
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Ok.....so then the info I posted on the neutral is what you needed.

FYI..... I will be separating your thread from the original one.
 
 

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