I don’t have the device, but I found the manual and the setting between F and C directly on the homepage of MCO Home. I always look for the first possibility on the homepage of the manufacturer. In most cases, manuals are available.
@DirkG you’re right, but I also understand @Tangodelta’s feedback.
In the old manual, that most home automation shops link to with their product details, this secret menu option is not mentioned. Also in the “old” documentation I received from MCO Home directly, this option is not mentioned; so MCO Home apparently updated their manuals.
That’s the reason why I always look for the manuals on the homepage of the manufacturer. Also, the manufacturer often provides manuals for older device versions or devices with older firmware.
Other websites like manuals.z-wave.info have a large selection of manufacturers and manuals, but some of them are outdated or incomplete. In addition, translated manuals sometimes contain translation errors.
Ok, sorry for my arrogant respons, I usually do my job before I ask for support. Found it fantross in your link, though a new question appeared, where is K1 and K2 keys? 
I have no way of knowing that. If you had mentioned it briefly, it would have been understandable. My answer was also not meant badly but only a hint.
There are also users who do not bother and go searching first.
Some or even many of us are not natural English speakers. In spite of a translation program, it is easy to misunderstand something.
Nevertheless I have found the relevant point in the manual (Online)… 
This is what I meant: You/we/I can misunderstand contents.
I didn’t find your answer to be arrogant, but as further information.
I guess K1 corresponds to “Key S1” and K2 corresponds to “Key S2”.
I would just give it a try, you can’t do much wrong, I guess.
Well, that was my thought too, logically, but nope…
Then I’m out. I can’t try it myself because I don’t have the PM2.5 monitor… 
Well, I guess the “secret menu” is very secret, will contact NSA, maybe they can help
The instructions are a direct copy of the instructions of the MH9 CO2 sensor…
So long press S1 + S2 is not working.
What are the remaining options:
Long press S1 + S3: inclusion mode
Long press S2 + S3: ?
Long press S1: Calibration settings interface
Long press S2: ?
Long press S3: Local time modification interface
I’d say two options to test…
Long press S2+S3 = --6.5 ?? S1 or S3 does nothing
Long press S2 = set (inclusion nr) f.eks 032 S1 and S3 for up or down
I think there is small bugs in app - at least with MH7H Thermostats.
Orange/Blue color not depend on state of heating of thermostat.
It would be nice to set real temperature on tile instead of target temperature.
It would be also nice to report power consuption depends on state of heating.
It is based on, if the target temperature is:
lower then the measured temperature (blue),
higher then the measured temperature (red),
or the same temperature (black-ish).
The developer has no further control over this.
This is not possible / not the implementation Athom prefers.
I can’t change this…
The thermostat itself does not report power consumption.
I can check to add a option to approximate the power consumptions based on the state of the thermostat.
But with the Zigbee update it will not be high on my work list…
I ment see, not set 
It would be nice to see real temperature on tile instead of target temperature.
That is what I responded to… has been requested many times before. Please address this question to Athom.
Hi Ted,
Quick question; is there a possibility to add the MCOHome A8-9 in the future? No hurry, but I’m planning for the new house and that product seems to have it all. Thanks!
@TedTolboom I don’t really need or want anything except to say a huge thank you for creating and maintaining the MCOHome app. I recently bought a Homey and MCO light switches and this works perfectly for me.
Thanks again
Any chance you could let me know Ted?
