HVAC thermostat

7 years ago

My mom's house is a manufactured home, and the thermostat shows no display even with new batteries, so I'm assuming it needs to be replaced. The house-wired connection is still good because the fan still works when I switch it on (even without the batteries). The heater, though, won't come on, so I'm assuming the display has to work for the heater to switch on??? However, I'm not sure if the wiring configuration on this thermostat is the "norm". There's just one wire from the wall, a big black wire that contains four others, red, green, white, and yellow. Will any simple replacement unit such as those $20 Honeywell models work for me?? Thanks!

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BobH

7 years ago

First, the batteries are typically just there to keep time and any programming in the t-stat in case power goes out. They won’t run the display.
If you only have 4 colored wires, then most thermostats made today won’t work because they require a 5th wire, typically black blue or brown, to be used as a common wire because the thermostat actually draws power to run itself. You will need to find a thermostat that doesn’t need the 5th wire or you can run the 5th wire yourself if it is not too hard.
The fan switch doesn’t depend on any relays inside the thermostat to work, so when you switch it to “on”, you are physically connecting the red wire incoming 24 volts a/c to the green wire. When the furnace gets 24 volts back on the green wire it turns the fan on.
It sounds like the thermostat is dead since nothing shows on the display. I would suggest trying to find the same model # thermostat on eBay and just swap it out.

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Comments (7)

sktn77a
7 years ago
What make of thermostat is it? You could just replace it with the same one.
HU-578702468 thanked sktn77a
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mike_home
7 years ago
You only need 4 wires for a non-Wifi thermostat. Are all the wires connected to the thermostat? Has this thermostat ever worked properly?
HU-578702468 thanked mike_home
weedmeister
7 years ago
" I'm assuming the display has to work for the heater to switch on??? "

Not exactly. It's more like, if the heat comes on the display will most likely work.
HU-578702468 thanked weedmeister
HU-578702468
Original Author
7 years ago
I don't know the model number or brand, it's not listed on the unit. Typical of manufactured homes! I will add this, however. The unit has always worked, but the display has indeed gone blank before. When that happened, I simply replaced the batteries and the display came right back on. So that's what has me confused. It appears that this older model style doesn't use the batteries as a backup but rather to operate the display as well as the temp settings and the heat/off/cool control, but not the fan control. This model isn't programmable in the sense that there's no memory settings or advanced temperature programming. All it does is allow temp plus or minus. Anyway, this time when I replaced the batteries, it didn't work to bring the display back up. I just don't want to go and purchase a cheap replacement only to find out that the four-wire setup isn't compatible with the replacement model.
User
7 years ago
There should be a model number somewhere on the back, perhaps within the battery compartment.
Stax
7 years ago
Call the home manufacturer and ask Model No.