I am trying to replace the timer switch for my bathroom exhaust fan. I found plenty of options, all of which come with colour-coded wiring (white = neutral; black = hot; red = load; green = ground), as in the picture below. However, these colours do not match the original switch (photo #2). Also, the original wires coming out of the wall are super thin. From my research and (very) limited knowledge, I sense the original blue wire is a remote control wire. For clarity, I live in a condo/apartment, and my bathroom fan is connected to the fan coil/central air handler in my bedroom, which has an ON/OFF "ERV" switch that must be in the "ON" position for the bathroom fan to work. The original timer replacement part costs $125(!), so I am trying to go for another option. Any suggestions/ideas/input are welcome. Thanks! 
2 Answers
The last photo is of a low voltage device, not mains voltage. The marking “remote timer switch” indicates that the actual timer switch is part of your air handler and this is simply a control panel.
Unless you want to do a lot of rewriting , I’m afraid you’ll need to buy the original part.
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Thank you so much for your time and for your input. Much appreciated. I have found this is, indeed, a low voltage - push button auxiliary/point-of-use control / timer switch for an Energy Recovery Ventilator (ERV) system, in this case for the bathroom exhaust fan. It seems every manufacturer has their own propietary timer :( Commented May 13, 2023 at 3:26
Well, we don't know what that proprietary switch is doing. It might have complex electronics and be talking on CANbus. Or it might just be a plain switch hiding in there that's just shunting 2 wires, and maybe the other 2 are for a backlight or something. We don't know. If it was the latter, you'd be able to use any plain switch. And the old-school spring-wound timer switches would work in that case.
It's not a case of "everything is proprietary and incompatible". It's a case that yours is. Generally there are 3 categories:
- 120V switching, using a plain "switch loop". It will only support old school spring-wound timers and a few pushbutton ones made to work with no neutral.
- 120V switching, with neutral present. That is what your fancypants pushbutton job is for, and it won't work on anything else.
These first two cover the vast majority of installations. However, they provide very little control.
- A variety of proprietary systems that use low voltage for stuff - GE RR7, what you have here, all sorts of different setups with varying degrees of compatibility, and the necessity of doing some engineering to read the manual and use the products accordingly.
You have this system. ERV's are awesome, and I wish more people would use it (instead of, say, non-ERV systems with a 12,000 watt makeup air heater LOL). But ERVs do not inherently need the fancy low-voltage control you are looking at. It could just be a regular switch like a normal bathroom fan.
That low-voltage stuff is there to do something fancy. I would consult the installer to understand why that was selected and what will be impacted if you defeat it.
