24Vac from Honeywell 7224 for wifi thermostat's c wire
Hi all,
My home has a Honeywell L7224 aquastat controller (manual) which is connected to a couple of two-wire Hunter battery-operated thermostats, which I am looking to replacing with Honeywell RTH9585WF Smart Thermostat (wifi) which require a C wire. At my skill level I can run wires so I'm not concerned about that.
Unfortunately the L7224 doesn't have a obvious C wire connection but I found an old but promising thread here, Wiring a new Honeywell Thermostat to Honeywell Aquastat Controller in which @PJmax suggested that there may be 24Vac between terminals marked T and 2 in the schematic. I measured this yesterday and I measure ~27Vac across those terminals, and ~13Vac between T and 1.
My question: can I connect the C wire to terminal 2 of this aquastat and pull it up to the thermostat?
Secondly, I have another zone in the basement, and also a hot water heater connected to this aquastat. How would I handle the second thermostat?
Here is photo of DH zone control panel mentioned in Post #7 showing easy to see wiring. No zones were active so only LED for 24 volt power was lit.
White page on upper left List 4 step to activate zone and basic color coded wiring for all zones. Labels on right side on have blue tape for thermostats across top and yellow tape wire for zone valves on bottom. Terminal blocks with screw make wiring and changes easy.
Panel is protected by removeable Plexiglass plastic sheet.
A second text sheet, out of picture, at bottom explains color codes and physical location of zone vales.
Bring all zone wiring to central panel makes life easier for both DH and future repair person. Post this hoping it will make it easier for others.
Modern thermostat use very little power for their electronics. The heating contacts, RH and W usually rated at 3 amps, far less than most heater T T controls draw.
How much spare power the L7442 has for other things, i.e. zone valve is another issue.
To simplify things am using one 24 volt 75 VA transformer for everything.... 8 zone vales, 5 thermostats, electrics stack vent, out-door-reset/aquastat, etc..
Caution, there can be issues using several 24 volt sources in one residence. That is why have separate RHeating and RCooling terminals for 24 volts to activate unit. If system has only one combo heating and cooling terminals are jumpered
.
@doughness Thank you for your reply and confirmation. Based on the following, I may not even need to worry about 24Vac from the aquastat...
@Astuff, You're correct, the thermostats are not directly connected to the aquastat. Your reply made me look again to see how the current wiring is set up, and while doing that I found something I didn't notice the first time: up high there is already a Honeywell AT72D1683 transformer which is supplying 24Vac to the thermostat on the hot water heater and zone controllers (valves?).
So only the two thermostats (1st floor and basement) are on old, two-wire connections. Given that, my plan is to pull new 18/5 to/from the two thermostats to replace the existing 18/2, and then hook up the Common wire from the AT72D1683 transformer to the Blue wire in the 18/5 bundle to the new thermostat. Does that sound right?
If GoHelloGo has typical system, thermostats contacts start zone valve motor. When valve opens, end switch closes to activate circulator or its controller. Wires from several end switches are connected in parallel to circulator for those zones. DH has 2 circulators activated by 8 send switches.
This another instance of Honeywell causing confusion by labeling L7224 an aquastat when is multi function item..
“The L7224U controls the circulator, oil burner and boiler temperature. “
That transformer is switched thru thermostats to zone valves. The zone valves then activate the boiler.
It would be best to post a picture or two of the wiring at the zone valves to confirm their wiring and C connection.
DH 1057 split level home started with one line feeding all elements. Over years, split to 8 zones, with thermostats and valves in various places and 2 circulators.
When issues arose, diagnostics, trouble shooting and repair was real challenge.
Some years ago brought all thermostat and zone valve wiring, laid out with labels in flow diagram pattern to 2 foot square plywood panel on wall at boiler. Also wires to activate circulator control on boiler and bring 24 VAC. LEDs show what's active.
For this low voltage & current wiring used round casing, interior line AT&T 4 wire #22 wire, and U shaped staples.
DH has long experience with complex systems, likes to simplify things.
When wife question temperature in some room show her boiler temp i.e. 165F then which thermostats and circulators active.
Thanks for the responses. Here are some pictures as @PJmax requested, which should clarify things: first an overall picture of the furnace; second a picture of the 24Vac transformer, and finally the junction box where I will make changes.
Refer to the junction box image: my plan is to replace the Thermostat #1 and #2 wiring which currently is two-wire, with a 18/5 cable, reconnect the two wires as they are today, and then use the Blue wire from the new cable and connect it to the "C" (white) wire from the 24Vac Transformer which is coming in from the top of the Junction box. With that done, my understanding is that I should be able to connect the new wifi thermostat which requires a C wire. Please review and let me know if I am about to do something crazy
First image is furnace, showing three zones (cellar, hot water and 1st floor), and the wiring which goes to the junction box
Furnace
Below is the transformer which supplies 24Vac and enters the junction box at the top AT72D1683 24Vac 40VA Transformer
Junction box showing wires (labeled in image). Thermostat #1 and #2 are two-wire (old), rest are all 18/5, except for T-T and the wires from the transformer. Junction box (yes, it's a mess!)
It's a lot of connections in a small space.
Your transformer may be labeled C and R but it doesn't mean that it was wired that way.
When only two wires is used to connect the stat.... there is no polarity or direction of colors.
What is important is that the one of the transformer leads goes to the R of the thermostat.
The W of the thermostat goes to the TH terminal on the ZV.
The other transformer lead goes to the TR terminal.
On these zone valves.... TH-TR is just a splice point. It doesn't connect to anything in the ZV.
That 4” square electric box is not required for low voltage 24 VAC thermostat wiring. Maze of wire nuts and jumbled wires looks hard to work on.
Terminal 12 strip in link below can join several #18 to # 22 wires and be cut to number needed, Every easy to add or remove wires. Link also has many useful items for heating systems
Here is photo of DH zone control panel mentioned in Post #7 showing easy to see wiring. No zones were active so only LED for 24 volt power was lit.
White page on upper left List 4 step to activate zone and basic color coded wiring for all zones. Labels on right side on have blue tape for thermostats across top and yellow tape wire for zone valves on bottom. Terminal blocks with screw make wiring and changes easy.
Panel is protected by removeable Plexiglass plastic sheet.
A second text sheet, out of picture, at bottom explains color codes and physical location of zone vales.
Bring all zone wiring to central panel makes life easier for both DH and future repair person. Post this hoping it will make it easier for others.
PJmax The wiring is as you show in reply #11 except the C wire not there (yet).
Good news is the rewiring the thermostat #2 in the basement with 18/5 and C wire is complete. Unfortunately ran into a snag (literally) with pulling cable up to the first floor for thermostat #1, and going to stop for the day. More as I get along further.
doughess Your set up is well organized and giving me ideas to do something better than the junction box in the future.
Happy to report that the 1st floor thermostat is also wired up with new 18/5, C wire connected to the smart thermostat, all running perfectly so far. Thanks to PJmaxdoughess and Astuff for taking time to reply to this thread. Much appreciated.
We recently had a nest thermostat 3rd gen installed and I don't think it's programmed/wired correctly.
We had our HVAC system replaced 2 years ago and I was told we have a 2 stage heat pump and 2 stage electric heat unit.
The unit numbers are HRG1660S1M and HCG60V1M-1.
I have no idea how the previous thermostat was wired but the person who installed the nest seemed worried when we told them how much our electric bill was during the winter, he said it sounded like the heat pump was not coming on, only the heat strips. He set up the nest and left. We had to call him back because only cold air was blowing (I could hear the outside unit on). After he adjusted a few items the heat came back on and that was that. Now I don't see the outside unit coming on. I touched the copper pipes coming out of the unit after the vents were blowing hot air and they were ice cold.
Below are pictures for current nest wiring, outside unit wiring and diagram, attic unit wiring and diagram.
Since he said we have a 2 stage heat pump with 2 stage electric heat, I asked we the jumpers for w1-w2, o-r-ds and y1-y2 were still on, he said they need to be installed for relay delays and that they don't come on all the time.
Anyhow, if someone can confirm if this is correct or not I would really appreciate it!
[img]https://cimg9.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/thermostat_wiring_current_fe52eefb25c144f48624f841ed50be5dede70d4a.jpg[/img]
[i]Current Nest Wiring[/i]
[img]https://cimg0.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/outside_unit_wiring_2fe45f8c56830628df5383208e33215349051ed7.jpg[/img]
[i]Outside Unit Wiring[/i]
[img]https://cimg8.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1200x2000/outside_unit_wiring_diagram_5b17d2299b8d7ad6b18fb048de337694e38d0885.jpg[/img]
[i]Outside Unit Wiring Diagram[/i]
[img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/attic_unit_wiring_17617b45facd0979925f6a2480fc45c6fd8e3e36.jpg[/img]
[i]Attic Unit Wiring and Jumpers[/i]
[img]https://cimg3.ibsrv.net/gimg/www.doityourselft.com-vbulletin/940x2000/attic_unit_diagram_43928f78abdbb697ed0ae780c2ee95c755da24f7.jpg[/img]
[i]Attic unit Wiring Diagram[/i]
I'll do my best to describe the problem I'm having in words as I don't think pictures will help, but I'm happy to be proven wrong. I am an IT guy with a very basic understanding of wiring and low-voltage, but by no means am I a qualified electrical engineer or electrician, making me probably a very dangerous person (know just enough to have the confidence to do something stupid).
I just moved to a first-floor condo of a 3-story building with my HVAC unit on the roof. I tried installing my Sensi Wifi Touch in place of an existing old-fashioned thermostat that didn't make use of the C wire, but was happy to to find that a C wire was present. I am certain at this point that it is a proper C wire as I've toned it out (initially to figure out which A/C unit was actually mine). Despite this, [b]the Sensi Touch, which worked fine at my previous residence, does not power on at all[/b]. So, I got to measuring voltages:
[b]From the wall inside my condo, when I measure the voltage difference across the C and R wires, it's just a little above [u]17v AC[/u]. [/b]This is clearly below the 20-30VAC specified in Emerson's documentation, so the unit failing to power on comes as no surprise.
[b]When I measure voltage across the C and R/Rc terminal at the actual rooftop air unit, it shows ~25v AC[/b] which seems right to me.
I have no idea what is causing this unexpected drop in voltage between the roof and my wall, but my only working theory as an amateur is that there's something wrong with the C wire itself that requires replacement (not something I want to do until I'm sure I've exhausted my remaining options). My setup also involves a G, O (G and O jumpered together on old thermostat) and Y wire (in addition to the Rc and C). When I measure the difference between any of these and the R/Rc wire from inside the condo, they all appropriately show as ~25v AC.
[b]Does anyone here know of any common causes of such a large drop in voltage or anything else I should try before hitting up an HVAC pro or electrician?[/b] I don't think it's sheer distance as no calculator I've used suggests the possibility of 18AWG wires dropping more than maybe 1v across 3 stories (which I roughly estimated at about 15 meters of cable/wire).
If they would prove useful, I'm happy to share photos or additional details or conduct additional tests as needed.
01-01-21, 11:39 AM
