Connect Nest Thermostat to Braemar TH5

[TTyndall]

Hi,

First up I’m not a tech head and this is my first post so please be kind…

I have an old Braemar TH5 heating unit. It is connected to a Spectrolink controller via a 4 wire cable (looks like an old phone cable). The Spectrolink is no longer receiving power via a 20m cable however when I plug in a short one it works. Could be a rat chewed the old cable and my new cheapo isn’t good enough…

anyway, I was thinking I might be able to bypass the whole problem by installing a Google nest. Can anyone please advise if this is possible? There was a previous post where someone asked the same question to which I think the answer was ‘it should work’ but the poster never replied to confirm it did! If the answer is ‘yes’ I might need some help to identify what wire to put where…

cheers

[CoolingWizard]

The TH5 can indeed be wired to a manual thermostat. You will lose quite a bit of functionality that you get with the SCC controller. In the actual system manual, this is what is stated. Here’s what it says about 24 V control systems.

” 24V "Manual" Thermostat
All TH series heaters can all be used with a standard 2-wire type manual digital thermostat. Connect a low voltage 2-wire loom between the thermostat and "T/STAT" on the BSC circuit board. Note that with Braemar TH series heaters zoning and evaporative or refrigerated cooler operation is not possible with these thermostats.”

The AC Cooling Wizard

[TTyndall]

Thanks very much CoolingWizard! Fortunately I don’t need zoning and it is only for heating, so I assume the Nest should at least enable programming based on times and temperatures?

The reason for the change is because I haven’t been able to get power to the Spectrolink. Assume if I run a multimeter on the 24V terminals this will confirm if I have power?

aside from that, I assume the wiring is pretty straight forward? The phone line wire used for the Spectrolink seems a little light in gauge?

cheers

[CoolingWizard]

With a multimeter you can check the board on the TH5 and verify the 24Vac power is available on the R and the C. When comes to the 4-wire cable, look closely at the bad cable at each and compare the color wires at each end and see if they end up at the same locations. Sometimes the manufactures will intentionally rotate two of the wires so it’s not a straight through cable. Technically, you could probably use a CAT-3 cable with the appropriate connectors at each end, wired the same way and it will work. Again, the key is how the each end is wired. Look closely you might see the color of the wires and you can tell if they’re both wired straight through or if there’s a rollover switch between two sets of wires. I also noticed the manufacture does not sell just the SCC cable. You have to buy the whole control unit to get the cable. 

AC Cooling Wizard

[Jenelyn_O]

Hi there,

Thanks for reaching out. I hope you get the answer you're looking for. To further assist you, please let us know if you still have questions or concerns.

I appreciate your help, @CoolingWizard.

Best,
Jenelyn

[Jenelyn_O]

Hi TTyndall,

I wanted to follow up if you still need help. Please let me know if you’re still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,

Jenelyn

[TTyndall]

Hi Jenelyn,

Thanks for following up. To be honest I haven’t yet had the chance to test the voltage on the board. I am also anticipating I might find voltage on the board which could leave me no closer to identifying the problem! With regard to the cable wire configuration, I actually have both as I incorrectly ordered the wrong one first time - unfortunately neither of them work!

at this stage I’m thinking I might pull the cables out from both ends - easiest fix will be if there is a break in the wire and I can repair it! I’ll do some investigating and come back to you!

cheers

Tom

[CoolingWizard]

@TTyndall , there is a technique to test the thermostat cable without have to pull it all out.  
1. Go the air handler, disconnect the thermostat wires. Take any two wires and hook them together in a wire nut.

2. Go to the thermostat end, and put your meter into continuity, put one test lead on one of the paired of wires, and the second test lead on the other. If meter reads OL one of them is broken.  
3. Try different parings until you can isolate any bad conductors. 

AC Cooling Wizard

[Jenelyn_O]

Hey TTyndall,

It sounds like a plan! You can also refer to the information provided by CoolingWizard. Please keep us posted. 

Thanks for your help, @CoolingWizard.

Regards,

Jenelyn

[Jenelyn_O]

Hi there,

Checking if you still need help. Please let me know, as I'll be willing to assist you further. 

Thanks,

Jenelyn

[Jenelyn_O]

Hello there,

Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know. 

Best,

Jenelyn