Honda heated seat

I think you are the victim of an otherwise good idea; theft protection that has disabled the electrical system.

I believe you will have better luck going to an MB forum and posting your question there:

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fuse is the go to area for electrical problems- if it keeps blowing fuse then look for problem in the seat cushion areas- Denny

F21 its a 20amp fuse

The following checks and repairs can help you:
1. In the fuse box within the bonnet - check fuse number 22, if burnt, replace it
2. Check fuse 19 in the fuse box inside the car located under the dashboard on the driverside
3. If these steps don't help, the problem may be with the wiring and connection between the module and the seat cushion - inspect it
4. Check if the signal return on the circuit is adequately functioning - if the module is being informed of an active seat
5. If there is a problem - repair or replace the circuit and/or wiring.

If you have an Owners manual, try looking for a fuse panel diagram. Your could have a bad connection inside the doorpanel which shorted the fuse. The seat drive motor must be wired to a separate circuit coming from the floorboard and its okay.
The circuits are wired independently to protect the lighter wires from the heavy drain of the seat motor. If you had the heated seat function working on the seat at the same time as adjusting the seat motor it would be too much for a single circuit, so they gave you two circuits.

If you are going to work on the door panel, disconnct the NEG battery cable so you won't short out something taking it apart.

Another Repair place you might try is a Glass Replacement shop. They install the inner workings of window tracks daily and remove the door panels to do it. They would be able to find your wires, test your window motor, and get you on your way quickly.

Unlike a Dealership, they have a high turnover of glass installations daily. Some even come to your house to repair your problem. Your car would be repaired more quickly with these services.

Check fuse, may have obstruction under seat, or motor may have short

Swap it with a relay you know to be good and see if it works again,pick a relay that is not important to the function of your car.

at temperatures such as yu mentioned the car will almost certainly suffer some sort of electrical problems as microchips which controll all your electricals are prone to breaking and loosing functionality. it could be either. if you can take motor off or access the main wires at the back of it and try direct connection to the battery and see if it responds. if not then it will definitley be a fuse.

(bad factory design) First keep large items from under your seat make sure nothing is hanging down or loose check each wire manually softly wiggle from side to side and up and down if something is loose more than likely that particular wire is the problem under there second make sure your passengers aren't placing shoes /feet under you seat and kicking the sensors or motor. you may need to change the seat temp sensor it has a fuse in it that is going bad from wear n tear or from leaving heated seat on after exit and shorting out when you turn on vehicle may be cheaper to go to junk yard and replace your seat(s) electronics for about $15- $35 when you clip the sensor wires make sure you leave enough wire to work with when you install same thing leave some existing wire to work with and cap off any loose wires with heat shrink wire protectors or gel wire protectors also change your fuse for your seats heat feature located in the fuse panel box remember to disconnect your battery before performing any electric maintenance. now here is the trick you need to get some tie straps and strap everything you see under seat up away from pesty passengers feet and from anything you may place under your seat If this doesnt work change out your seats from Junk Yard the seat wires my have a short in them and you cant get to all of em without destroying the seat(s) integrity