Chronotherm III T8600 C1014 - http://www.hvacmechanic.com/ Forums

Original message

javelli

81.69.66.208

"Chronotherm III T8600 C1014" , posted Sat 10 Apr 07:21

I took over a Chronotherm III T8600 C 1014 to replace a simple 2-wire round shaped Honeywell (don't know the type, but it has a mercury switch) manually operated thermostat. I want to control my Saunier Duval SD623 central heating system with it.

However, I cannot get it running. I connected the two wires to terminal W and R. The display keeps showing -AC telling me that there is no power from the system. But when I shortcircuit W and R the heating starts working. When I measure the voltage on W and R my volt meter indicates 40 VAC.
What could be wrong ?

Replies:

Xenos
Webmaster

69.156.57.202

"Re(1):Chronotherm III T8600 C1014" , posted Sat 10 Apr 07:32

Snce this is a power stealing thermostat you may need to install a 270 10 watt resistor between W and common at the furnace.

Xenos.

The best way to escape a problem is to solve it.

javelli

81.69.66.208

"Re(2):Chronotherm III T8600 C1014" , posted Sat 10 Apr 08:42

What does this resistor do to make the thermostat work correctly ?

Xenos
Webmaster

69.156.57.202

"Re(3):Chronotherm III T8600 C1014" , posted Sat 10 Apr 17:10

OOPS I was asuming you had the thermostat powered. -AC means it's not powered.

Make sure your reading 24vac between R and W.

Xenos.

The best way to escape a problem is to solve it.

javelli

81.69.66.208

"Re(4):Chronotherm III T8600 C1014" , posted Sun 11 Apr 01:35

As a matter of fact I measure 40VAC between R and W. When the furnace is on, a current is drawn of 0,2 A.

Xenos
Webmaster

69.156.57.202

"Re(5):Chronotherm III T8600 C1014" , posted Sun 11 Apr 09:13

OK I’m baffled the current draw is good and it should work. Now I have never saw a furnace with a 40 vac control system and that thermostat is designed for 24vac maby this is the reason.

P.S. the R wire is connected to R and not RC correct?

Look here and note the control modules it will not work with, maybe you have one of these modules and it’s the 40 vac thing.

http://hbctechlit.honeywell.com/techlit/PDF/69-0000s/69-0339.pdf

Xenos.

The best way to escape a problem is to solve it.

javelli

81.69.66.208

"Re(6):Chronotherm III T8600 C1014" , posted Sun 11 Apr 15:42

The furnace I have (Saunier Duval SD623), is not listed in the Honeywell table. According to the Furnace manual it is definitely a 24V system, but when I measure at W and R it is 40 VAC.

Is there any way to check if the Honeywell T8600 C1014 Thermostat is working well ? Can I put simply 24VAC on W and R and see what happens ??

In the manual I have of the furnace it says: To control with a clock thermostat - type with potential free contact.
What would this mean ?

Xenos
Webmaster

69.156.57.202

"Re(3):Chronotherm III T8600 C1014" , posted Sat 10 Apr 15:34

It puts a load on the thermostat witch causes curent to leak through the W terminal and thus powering the thermostat. Most furnaces can do it some require a resistor.

It should be listed in the back of the manual.

Xenos.

The best way to escape a problem is to solve it.

Xenos
Webmaster

67.71.21.252

"Re(4):Chronotherm III T8600 C1014" , posted Sun 11 Apr 15:46

What ignition control does the furnace have? Look it up in the table.

No you cannot put 24 vac on R to W as the reading your getting through W is a finding a potential difference through the module and is not common.

Now you could power R and have W powering a relay with the other side of the relay connected to the transformers common.

Xenos.

The best way to escape a problem is to solve it.

javelli

81.69.66.208

"Re(5):Chronotherm III T8600 C1014" , posted Sun 11 Apr 16:13

The ignition system is done with a pilot flame. If this is what you mean.

For my understanding. The old thermostat I want to remove is a two wire thermostat. On these wires I measure 40 volts when the furnace is not heating. When the furnace is on, the measured voltage is zero, because it is short circuited by the thermostat switch. Don't I need a third wire to keep the thermostat powered ?

Xenos
Webmaster

67.71.21.252

"Re(6):Chronotherm III T8600 C1014" , posted Sun 11 Apr 17:49

This thermostat does not require a common as long as there is enough leakage (potential difference) caused by current flow. If there isn’t a resistor needs to be installed between W and C at the furnace.

Xenos.

The best way to escape a problem is to solve it.

javelli

81.69.11.17

"Re(7):Chronotherm III T8600 C1014" , posted Tue 13 Apr 08:14

I am looking at a list of different types of resistors. What kind of resistor can be used best for this purpose (Cermamic, Thick film, wire wound.......).

Xenos
Webmaster

198.96.185.7

"Re(8):Chronotherm III T8600 C1014" , posted Tue 13 Apr 20:42

The only specs they give for the resistor is 270 ohm at 10 watts

Xenos.

The best way to escape a problem is to solve it.

javelli

81.69.66.208

"Re(9):Chronotherm III T8600 C1014" , posted Fri 16 Apr 16:49

Now I have bought a resistor.
You wrote that I have to put it between W and Common at the furnace. I cannot find the 'common' indication in my furnace.

I see L, N and earth of the mains (230 VAC) wire and I see the thermostat wires blue and red at terminals marked with 2 and 3.

Where to put the resistor ?

Xenos
Webmaster

67.71.21.107

"Re(10):Chronotherm III T8600 C1014" , posted Fri 16 Apr 18:20

Common is the opposite side of that low voltage transformer. One side is power the other is common.

Xenos.

The best way to escape a problem is to solve it.

javelli

81.69.66.208

"Re(2):Re(10):Chronotherm III T8600 C1014" , posted Tue 11 May 15:56

Finally I found the solution. My furnace did not give the right voltage. I am not sure if it is AC or DC or some mix of it. In any case the thermostat needs pure AC. I now bought an AC adaptor which feeds the thermostat. In this circuit I put an AC relay which switches the furnace now. When the thermostat switches to 'heat on', the boiler starts.
Thanks for your support and tips !!