cancel
Showing results for 
Search instead for 
Did you mean: 
Replies are disabled for this topic. Start a new one or visit our Help Center.

Replace older Honeywell chronotherm

jasonpowell
Community Member

My antique chronotherms have separate wires going to clock terminals for the clock in the thermostat.  These are in addition to the wires for y, w, & r furnace terminals.  
my presumption is that these clock wires should be capped, taped and left in the wall.  Anyone have a different conclusion?

43 REPLIES 43

CoolingWizard
Platinum Product Expert
Platinum Product Expert

I have replaced many of these types of thermostats and you can just tape off in tuck away those wires that go to the clock. All you need is the R,Y,G,W, and C

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

The Chronotherm I have (actually, I have one on first and second floors) controls both heat and ac.  It only has the following wires, black wire to Y terminal, white wire to W terminal, and red wire to R terminal.  As I said earlier, there are separate wires (white and red) going to the clock terminals. 

I've installed the Nest learning thermostat with the black wire to its Y1 terminal, the white wire to its W1 terminal and the red wire to the Rh terminal.  Unfortunately, the Nest doesn't respond,  I hooked it up to a charger as recommended and tried reinstalling it once the Nest indicated to do so.  No difference. 

Your thoughts?

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Please allow me to provide a little more details on the  Chronotherm. There are a couple approaches to power the timer clock.  One has a jumper from R terminal to one of the clock C terminals.  The second clock C terminal is wired to the HVAC transformer Common.  The second way is to have a separate wire connection from a dedicated transformer.  Yours appear to be the second approach. Now, get a multimeter and let us check the power source.  

Set the meter to AC Voltage, put one lead on the R terminal and the second to the wires, one at a time, that were attached to the clock C terminals.  You are looking for 24-Volts AC +/- 4 volts. It is more than likely the White wire at the Click. When you find it, that wire is the Common that can be placed in the C on the Nest.  You old R wire should be placed on the Rc of the Nest backplate.  The Black wire goes on Y1, the old W wire goes to W1 on the Nest backplate. 
It does not appear you have a G wire for your Blower Fan.  The Chronotherm did not have a G terminal since it relied on the HVAC equipment to control the Blower Fan. That should tell how old this thermostat is.  

Ken, The AC Cooling Wizard is 

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

4CDCD8DD-36C3-4885-8EF6-6DBBE0BD5BAF.jpeg

 fyi.   The main body indicates it’s a T882A 1047 if this makes any difference.  

CoolingWizard
Platinum Product Expert
Platinum Product Expert

It makes no difference. Just use the multimeter and find the common. 

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

The voltage between the red and white clock wires is 24 volts.  Between the Red wire for the R terminal and the white clock wire is about 6 volts, and between the Red wire for terminal R and the red clock wire is about 19 volts.  Assuming that I connect the red clock wire to the C on the nest and the old red wire to Rc, what would I do with the remaining white clock wire - if anything?

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Just tape it off and stick it back into the hole.  Or, repurpose it as the Blower control wire. This will require some rewiring in the Air Handler.  

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

I just tried with with the wiring as you suggested:  black to Y1, white to W1, red to Rc, red clock wire to C.  That didn't work, so I tried putting the white clock wire to C.  same response. 

Question:  Since the only time I had a reading of 24 volts was when I put the meter on both the red and white clock wires, and the unit doesn't power up when I plug one of them into the C terminal, should both of these be plugged in somewhere on the Nest backplate?  While it seems logical to my electrically non-educated mind, I didn't want to take the risk and try it on my own.

zoeuvre
Community Specialist
Community Specialist

Hello folks,

 

Thanks for lending a hand here, CoolingWizard. 

 

@jasonpowell, I wanted to ensure you were good to go. How's it going with your Nest Thermostat? Please let us know if you are still having any question from here, as we would be happy to take a closer look and assist you further.

 

Best,

Zoe

I'm afraid that I've returned them.  Despite tons of advice, nothing seemed to work.  A local hvac technician assessed the situation and recommended changing a number of older system components that would allow the Nests to work.  For the time being at least, I've returned to use of the old thermostats.

Jake
Community Specialist
Community Specialist

Hey jasonpowell,

 

I understand switching back to your old device. With that being the case, I am going to go ahead and lock the thread in 24 hours. Let me know if you have any further questions from here, as I would be happy to take a closer look.

 

Best regards,

Jake

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Your system likely has two separate transformers. It sounds like the transformer from your air handler system is not probably working correctly. What you need to do is attempt a simple test.

What we can do is take the RC wire out of the nest back plate and touch the bare copper wire to the bare copper part of W1 wire. After about three or four minutes, your heater blower should turn on. And warm air should be flowing. If that does not work, then chances are we need to check to make sure that the transformer is receiving power in your air handler. The same would be true if you took the RC wire and touch it to the white one wire that would cause your air conditioner to come on.  

please let me know how the test turned out. 

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

jasonpowell
Community Member

I did as you suggested.  As soon as I touched the Rc (red) wire to the W1 (white wire) the furnace started. 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Jason, this proves to us that there is incoming power from the air handler‘s HVAC transformer on the red wire, coming to the thermostat and attached to the R terminal. Furthermore, we know that the white wire at the thermostat attached to the W does indeed connect to the furnace control board. As for the blower fan that is controlled by the integrated furnace control board since you have no wire attached to the G terminal of your thermostat.

for the best possible charging arrangement, it is best to have a common wire attached to the C terminal of the nest thermostat back plate. If you’d like to rewire your air handler to bring a common wire using one of the clock wires, let me know, and I’ll help you to proceed.

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Yes, let's proceed.

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Do you have access to the air handler?

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Yes, one way or another 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

On the front of your Furnace/Air Handler, you will see where the power and thermostat cable got into the cabinet. That panel in front that entry point is the one that you need to remove. Sometimes there are held on with screws and sometimes they are twist knobs.  When you open that panel, you will locate the two thermostat cables that are coming into there. One will be the one with only your red and a white wire, that will be your clock cables, the other one will be the one that has the red black and white wires inside. Before we make any wiring changes, let’s locate things.   Look closely and do you see a control board with terminal screws R, Y, G, W, C? Look for the second cable with just a red and white wire? Does go to a separate transformer by itself? BTW generally on the side will be the make and model number.  Get that to me I can pull out the service manual for it. 

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

IMG_6038.jpeg

 Attached is a photo of the model # label.

Regarding the wires,  there is a control board of sorts with the terminals/wires as follows: 

IMG_6041.jpeg

 R is in the upper left corner (red wire), note white wire capped, C is upper right with black wire, W is in lower left - nothing attached, G is lower middle with a blue wire, Y is lower right - nothing attached.  

IMG_6043.jpegFYI, the wires from the furnace appear to go to these transformers labeled for the zone 1 (upstairs) clock, downstairs clock, the AC, and the various dampers - which don't seem to work well (when the downstairs thermostat starts the furnace it heats the upstairs as well  (old age?)

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Your control system is fairly old.  The Chronotherm thermostats were the first thermostats that could do both Heating and Cooling at the same time. The clock would be set to cool during the day and heat during the night.  Prior to the Chronotherm a home owner would have to go to the basement and light the furnace manually at night.  
I am not familiar with how they have wired up your system.  What I see is the Chronotherm clock had its own dedicated Transformers and the AC transformer is used only to power the outdoor compressor/condenser unit.  They have that Heat/Fan/Cool switch downstairs that frankly is wired to make the blower operate and lower speed for heating and max speed for cooling.  However, the temperature set point is done at the Chronotherm. This makes me think the W and Y wires go from the Chronotherm to the Heat/Cool switch in the basement. When in heat mode, the switch controls the burner and blower fan.  When the switch is in cool mode, it controls the blower fan and the outdoor compressor.

I need your help to see where the two wires on the AC transformer go. I think that the red wire gets cross connected and sent to the Chronotherms. Can you confirm that? 

The AC Coolimg Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

You are correct regarding the Heat/Cool switch.  The two wires from the AC transformer go into the Mastertrol Mark V box as follows:  At the transformer there is a gray wire at the top terminal and a red one at the bottom, as well as an unattached green wire wrapped around the cable.

IMG_6045.jpeg

 At the Mastertroll, on the left side, the gray wire from the transformer goes into the Yellow wire nut.  and the red wire to the "Common R" terminal.  Also there are two gray cables in the area that resemble the cables that enter the furnace, each with both red and white wires.  The white wires are joined with the gray wire from the AC transformer in the yellow wire nut. 

One red wire attaches to the "Fan G" terminal, while the other red one attaches to the "Comp Y" terminal (above G).

IMG_6046.jpeg

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Your control system is fairly old.  The Chronotherm thermostats were the first thermostats that could do both Heating and Cooling at the same time. The clock would be set to cool during the day and heat during the night.  Prior to the Chronotherm a home owner would have to go to the basement and light the furnace manually at night.  

Your thermostats are connected to Zone1 and Zone2 of the MasterTrol zone controller.  The three connections are T4, T5, and T6.  T4 is W, T5 is R, and T6 is Y.  Normally we would wire the Nest Thermostat to the MasterTrol using 4-wires. Your cable only has three wires.  You need to make a decision at this point. Do you want the Nest to be in total control or just be the zone damper controller like your Chronotherm were doing? The simplest would be to bring a common wire using one of the clock wires, the second would have us rewire your MasterTrol by wiring your Nest Thermostat to the T4, T6 an R and Common.  What would be you desire?

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

I bought two Nest thermostats assuming that I'd have one for each zone, just as the Chronotherms are "supposed to do."  I used quotes because, as it appears that the dampers are not working as intended, but that's another issue and would explain why, whenever the zone 2 thermostat called for heat, it was being provided the zone 1 registers as well.

Thus, if we are having the Nest thermostats, as you say, "be the zone damper controller like your Chronotherm were doing," which of the wiring options do you suggest? 

 

Once again, thanks for your time.  I'm quite sure there are otherthings youd like to be doing.  I appreciate it very much.

CoolingWizard
Platinum Product Expert
Platinum Product Expert

It sounds like one of your zone damper motors is not closing.  Your zone damper motors have a closing spring and power open.  It is likely that one of the springs has broken and the zone 2 stays open. As for wiring, if you want to make the thermostat be the controlling point for heat and cool, you need to pull new cables from the basement zone controller to the thermostat locations.  

I suggest we simply take a single step.  Disconnect the two thermostat clock transformer wires.  Then connect the white wires of those two cables to the Gray wires with the yellow wire nut on them.  Wrap the red one around the outside of the cable like the blue one was done. At the thermostats, connect the white wire to the C of the Nest backplate. 

Ken, The AC Cooling Wizard 

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Pardon me if me questions seem a little dense, but I want to double check my understanding.  I think I got it right but let me confirm that I'm looking at the correct wires.  To recap, currently, each zone has its own transformer with its cabling that carries 24V running separately and directly to each Chronotherm's clock.  I am to remove the wires attached to the exterior of each zone transformer and add those white wires to the yellow wire nut in the MasterTrol.   I then wrap the remaining red wires as you describe and at the thermostat connect the other end of the white wires to the C terminal on the Nest backplates and cap the red wires.

Presumably, I would then wire the Nest with the furnace white wire to W, black wire to Y and red wire to Rc or Rh (not sure which one).

CoolingWizard
Platinum Product Expert
Platinum Product Expert

You were doing fine don’t worry about questioning and asking for more help. What I am suggesting we do is disconnect, the red and white wire from the clock transformer labeled number 1 and number 2. Those transformers only powered the clocks within the Chronotherm. Disconnect the red and white wires from those Transformers.  Take the red wired and wrap it around the outside of the cable.  Route the cable into the MasterTrol cabinet and connect the white wire to the gray wires within the yellow wire nut. This will be the COMMON you need for the C terminal of the Nest.  And yes, put the R,Y and W wires on the Nest at Rc, Y1, and W1. You not need to cap the red wire since it will be wrapped around the out cable at each end. 

Ken, The AC Cooling Wizard 

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

It didn't work. Still no response from the Nest.   FYI there was one difference in the cables from the clock transformers.  The cable from the zone one transformer did indeed have red and white wires.  The cable from the zone two clock transformer had a red and a gray wire - which I connected as if it were the white wire.

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Let me make sure I understand you correctly. You were saying that connecting the zone, one white wire and the zone, two gray wire to the gray wires that are under the yellow wire nut, then connecting the other into the nest backplate C terminal did not get you Common?

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Yes, that's correct. 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Hmmm, OK, your going to have to untangle the cables so I can see the what goes where. I tried to decipher the cable from the HVAC transformer but it appears that the thermostats are using a different transformer.  Let me go dig out the manual for old zone controller. Since the thermostats are using the zone 1 and zone 2 connection points the T5 is getting its power form the 24 VOLT 40VA transformer connection that is to the lower left. We need to verify using a voltmeter between T5 and the number 1 and number 2 terminals. One of those will report 24Votls and that will be the common you will need to use. 

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

jasonpowell
Community Member

I moved the wires a bit in this picture.  I note that the 110 V cabling enters the outlet box to which is attached the Zone 1 clock transformer and that the Boxes with the transformers for the AC, both zone clocks and the dampers are connected to the 1st box for power.  I confirmed that the wires from the AC transformer have a green wire wrapped around the cable as well as red and gray wires that enter the Mastertrol with the gray wire connected to the yellow wire nut and the red wire connected to the R common terminal depicted on the left of this photo.

IMG_6055.jpeg

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Hang in there Jason, we will get this figured out.  At the thermostat locations there should 24 Volts AC power between the Red R Wire and the Clocks white or Gray wire.  Can you check that? 

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

While the clock wires are no longer connected to the transformers but are rewired as noted before, I can confirm that the transformers for the AC, and Zone clocks show 24 volts. 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

At the thermostat location do you detect the 24 Volts?

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

CoolingWizard
Platinum Product Expert
Platinum Product Expert

It took a lot of digging through some old binders, I found a note from a 1971 installation of a MasterTrol controller.  According to the note, then common for a thermostat is to me the M1 connector for the same zone.  Can you get the White wire and the gray wire to the M1 connectors?

 

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Getting back to your previous reply.  After reconnecting the wires to the zone one clock transformer, I can confirm 24 v at the transformer and between the red/white wires at the thermostat location.  Connections between either of those wires and red/white/ black wires of the thermostat yield less than about 2 volts. 

I’m not following- looks like you missed or messed up a word??

CoolingWizard
Platinum Product Expert
Platinum Product Expert

On that zone controller, you will see M terminals at the bottom that control the damper motors. My manual says that if a thermostat needs a Common wire, connect that common wire to the M5 location.  So one M5 gets the white wire, and the other one gets the gray wire. Once again the gray and white wire will be the Common at the thermostat. 

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.