'HELP! Replacing Honeywell T4039 with Honeywell TB6575A1000'‏

whitemamba · 01-27-2010, 12:14 PM

Fan coil 4 pipe system. I connected the wires and double checked them. I did everything right but the digital model display did not light up.

Then I measured the votage and it showed zero. I reinstalled T4039 (old one) and it is working fine but no voltage reading. Both models are 120 V. I must have lack of knowledge at some point. Does it matter if I shut the system off from the thermostat first then the heater switch before removing the old one? Can please someone tell me what I'm missing.

Thanks in advance.

**beenthere** · 01-27-2010, 04:11 PM

The 4039 didn't require a neutral to the stat. The 6575 needs a neutral.

Do you have a neutral at the stat?

whitemamba · 01-27-2010, 06:01 PM

You are right. I thought about the same thing and I connected the neutral (which is the white wire of 6575) to the junction box. Wouldn't that work?
Thanks!

**beenthere** · 01-27-2010, 06:26 PM

The j box may be grounded. But it is not a neutral.

And may not work.

It is also an electrical code violation.

whitemamba · 01-27-2010, 06:27 PM

So what do I do?

**beenthere** · 01-27-2010, 06:35 PM

Either use the old stat. Or run a neutral to the stat j box.

Can you convert one of the blower sped taps to a neutral. Or do you need all 3 speeds.

whitemamba · 01-27-2010, 06:37 PM

I'll try to run a neutral. If not I may try to eliminate one of the fan speeds. You've been very helpful beenthere. Thanks!

whitemamba · 01-27-2010, 07:11 PM

One more question, if I took a cord with a plug and stripped both wires and connect them to the thermostat's hot and neutral wires and plug it to a 120V outlet, would the stat turn on since it is 120V? Would that be a good way to check if the stat is not defective?

**beenthere** · 01-27-2010, 07:18 PM

If you disconnect ALL of the other wires from the fan coil. Yes, you can test it that way.

whitemamba · 01-28-2010, 01:09 PM

Hi beenthere.

I will try to attacj the problem tonight and I wanted to make sure I understand where to get the neutral from. All the cables come from a bow which is in the ceiling and I believe it is the fan. I will open that box and find the neutral if it exists. Is it possible that there is no neutral coming to fan? If there is a neutral, how do I know which wire it is? There is also a power switch attached to the box which shots off the system. Thank you very much for your help. I promise to pass alone the knowledge you give me when needed.

**beenthere** · 01-28-2010, 02:55 PM

If the blower motor is 120 volt, there will be a neutral at the fan. if its 240 volt. probably won't be a neutral.

And the second leg would need to be ran to the N terminal of the stat.

whitemamba · 01-28-2010, 02:58 PM

I will check and see if it is 120. If 240V than I have no chance of using the new stat since I am missing the neutral?

**beenthere** · 01-28-2010, 03:02 PM

If its 240 volt. You don't need a neutral.
Find out what it is. Then we can see what you need to do.

whitemamba · 01-30-2010, 01:36 PM

Hi Beenthere,

I just checked the wiring of the system and I am a little disturbed. They converted the system to 24V but used a 120V thermostat. Is this possible? I was thinking of pulling cables from the 120V source and connect it to the thermostat and use existing fan, heat and cold wires but I am not sure if the stat will sand 120V signals to the system which would blow it. I think we are getting close to a solution but I don't want to return the stat since I stripped the cables and they may not take it back (prothermostat.com). I am open to ideas at this point. I can even send pictures of cables and transformer connections if you send your e-mail. Mine is whitemamba at hotmail dot com.

Thanks and have a great weekend.

**beenthere** · 01-30-2010, 02:12 PM

Just post the pics here in this thread.