Original message
| Quizno
 |  "Upgrade from Lennox Mercury to Honeywell"
, posted Wed 9 Jun 00:52  
I'm stumped. I'm upgrading my old Lennox thermostat to a new Honeywell CT3500. I believe that the system is a heat pump but not sure. Theres a condenser outside with the airhandler inside. The old wiring was as follows:
V - Blue
R - Brown
F - Green
M - Red
Y - Yellow
X - White
The new stat has the following connections:
R
Rc
W
Y
G
O
Bb
Which wires go where??? I tried to get info from the Lennox site, but there was none to be had. Same with Honeywell. I'm burnin up here :)
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Replies:
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| HVAC Doc
| "Re(1):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 17:25:
Ok Quizno here is the wiring diagram for the old Lennox Stats:
X- Transformer common or C terminal
V/VR- Transformer R terminal (hot connection)
R- O terminal change over for cooling call
F- Fan output goes to G terminal
M- Y1 1st stage cooling
Y- Goes to W2 second stage heat.
Y1 and W1 will need jumpered to provide 1st stage heat (heat pump). Now that I have looked closer, it does not appear that your new stat is a 2 stage heat pump compatible stat. If thats the case, you need to get a different stat.
[this message was edited by HVAC Doc on Wed 9 Jun 17:51] |
| xenos
Webmaster 
| "Re(1):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 07:54
Not 100 % sure but I belive this is correct, the X that I don't remember as it could be emg heat.
V - Blue = R power
R - Brown = O reversing valve
F - Green = G fan
M - Red = Y compressor
Y - Yellow = W heat
X - White = C comon
Xenos.
The best way to escape a problem is to solve it.
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| | Quizno
| "Re(2):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 10:24:
so which one do I hook up to R then? Blue or Red? And am I supposed to see voltage on the wires at the stat?
Also, when I look at the unit inside, there's a terinal block on the top of the unit with 4 connections. There are 2 wires coming from each and I'm not sure what they connect to.
Any help is GREATLY appreciated :)
[this message was edited by Quizno on Wed 9 Jun 12:01] |
| | xenos
Webmaster
| "Re(3):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 17:33
The honeywell R ? it would be V or blue.
Xenos.
The best way to escape a problem is to solve it.
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| | Quizno
| "Re(4):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 18:18
Well, come to find out, this thermostat isn't even compatable with my system. I have a 2 stage heatpump with aux. heat. Now I gotta try and find a Honeywell CT3611 or T8611. What a bummer.
Anyways, I tried to hook my old theremostat back up so that atleast I can have cold air, but now THATS not working. I think I may have blown a fuse or something while I was wiring the other one. My model number is CB18-31-3P. What should I look for on the unit? The main circuit breaker pannel is normal with no blown fuses.
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| | HVAC Doc
| "Re(5):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 20:37:
Well you learned lesson number one, always turn the power off before wiring/unwiring anything on your system. Soem had a resetable breaker switch near the transformer or an inline type fuse. If you do not have either of these, chances are you fried the transformer. If you have a volt meter, find the two low voltage leads coming off the transformer and see if you have 24v. coming out.
[this message was edited by HVAC Doc on Wed 9 Jun 20:37] |
| | Quizno
| "Re(6):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 21:27
I checked the voltage and I have 120 coming off the transformer. Is that right? I do have some contacts where it is 24V, but not going to the thermostat. I was able to find the contactor on the outside unit and got it to spin up, but the blower inside was not operating.
Is this something I can fix myself, or should I get a service tech out here. I'd like to fix it myself cause the price of the service is kinda outrageous.
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| | HVAC Doc
| "Re(7):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 21:43
Ok so you have 120v. going into the transformer and stepping down to 24v. You need to locate the component(s) or wires that are shorted not allowing the 24v. circuit to be complete. I understand you feel a service call is too much to pay, but keep in mind that you could end up shorting out more components in your attempt to fix it yourself and costing you more.
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| | Quizno
| "Re(8):Upgrade from Lennox Mercury to Honeywel" , posted Wed 9 Jun 22:16
I take that back. I think it may be the transformer. I have 240V coming in one side and 0 on the other. When I test 2 of them (1 from each side of the transformer) I get 120V, but not when I test 2 from the non-240V side.
I'm going to have a service tech come out and take a look. Plus I think I'm gonna have them do the install of a new digital stat. Oh well, needed to get it serviced anyways :)
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