Blank Screen on Coleman Mach Digital Thermostat

Have you tried replacing the battery in the thermostat?

IF you state your existing tstat IS a RVP(coleman), and you have a blank display, I would bet you have a wiring (power) problem and NOT a bad Tstat. Soime RVP tstats have a on board fuse(glass). Some receive the power(12 volts) from either the furnace or the roof AC. I cannot remember if I ever have had a RVP tstat go "blank" on display that was not power supply related. Of course I only have over 43 years as an RV tech:B On amazon. The LCD Tstat for an RVP is $100. I cannot believe you purchased one for $25. NEVER, unless it was a stolen tstat and then sold on line. Doug

Thanks dougrainer for the advice!

The last time I used the trailer was in August. It wasn't hooked up to shore power and had battery disconnected since. I was prepping the trailer for a trip last weekend and noticed the blank screen on the thermostat. When I switched on the fan manually it worked so I assume there's
12V power supply to the thermostat. Anyway, I will try poking around with a voltmeter to see if I can get anywhere. Disclaimer: I'm no expert in electronics.

When I bought my last Tsat on Amazon.com, it was pre-pandemic and we shopped cross-border and it costed me $50 USD. Exchange rate was quite favorable to CAD then. Since the pandemic shut down, most of the mail collection services on US side has gone out of business. The latest asking price on Amazon.ca (Canadian site) was $285 CAD. With sale taxes and possible import duties and/or brokerage fee added, it could cost a lot more.

Our thermostat went blank a couple years ago during a hot, week long trip. Did some quick research, found the 12v power supply wire for the thermostat comes from the furnace. It was labeled "thermostat +12v". There was 12v there, but not at the thermostat. I hotwired it to a light switch right below it, that that is how it works to this day.

Update:

Today I decided to take a voltmeter to poke around the thermostat to see if there's actually a power supply problem.
Found a manual online and identified the color of the +/- 12VDC connections on the circuit board. There's 13+V across the blue & red wires. Took the circuit board out from the casing to see if there's anything obvious like loose connections or pinched wires. No luck. I reassembled everything together and prepared to throw in the towel. I thought to myself since I only took out the onboard fuse & visually inspected it last time. Why don't I check it's continuity with the ohmmeter meter and it's not blown.
However, when I reinserted the fuse back in, miracle happened. The digital display works again. Only explanation I can think of is it reset itself after power off long enough.

Years ago there was a very popular home computer that had plug in cartaridges. One of which was a MODEM and it tended to be plugged in once and left there for all time.... Well frequently they would fail.. you unplugged. plugged back in and Viola they worked.. WHY?
The answer: There is a virus among us. and it loves low current electrical connections.. and as it grows. it insulates the connection.

When you removed and replaced the fuse you cleaned it.

Suggest some DE-OX-IT two types.. First is the de-0xidizer This will have a number after the name LIke De-Ox-it 5 or De-OX-IT 100 (5 percent and 100 percent strength. I have both in stock) And then there is De-Ox-It Gold.. that is the protectant.

GOt the good stuff at Micro Center Used to get it at Radio Shack