Getting a common wire from air-handling unit to thermostat?
by
Georgi Peev
+4
I'm trying to replace the existing old-school thermostat with a Nest, but there are only two wires between the air-handling unit (
SpacePak ESP-3642D) and the thermostat (green and red, no common wire), and the Nest wouldn't power up.
First off, is it reasonable to believe the problem is the common wire, as my google searches indicate?
If so, I have some 18-gauge wire that I can easily get between the air-handling unit and the thermostat, but when I opened it up to see where to connect the common wire on the AC, I found no indication or labeling on the terminals other than numbers (see pictures).
Can anyone help me figure out where to connect the common wire on the air-handling unit?
Here are two manuals for you. Wiring diagrams are in step 7. Hope this helps.
https://www.acdirect.com/media/catalog/files/spacepak_horizontal_air_handler_installation_operation_and_maintenance_manual_model_espd_series.pdf
https://www.acdirect.com/litlibrary/ESPD.pdf
Anything William writes about HVAC, he’s the authority, as that’s his profession. 😎
Check your owners manual and that should be of help. You could also ask customer service on the company's website. Good luck and stay safe!
and if all else fails, go to youtube.com for videos of what to do - we have learned so much doing this
Thanks guys. The manual that William linked proved helpful, it seems that L5 is the likely common wire terminal I should use.