Question on fuse size

The air conditioner is run via 120VAC, and will have its own circuit breaker.

The fuse in question powers what exactly? Something that was added... Thermostat maybe? Something the previous owner did. Pull the fuse and see what stops working. Unless the wire is small (18ga or smaller), I wouldn't worry about the fuse being a 15A.

The empty slots are usually spares. I added a 12V cig-style plug near the bed in my trailer for a car charger for my phone, and used one of the spare slots and added the appropriate fuse for the wire I pulled (15A).

Yes replace with a 7.5 amp fuse. If the 7.5 opens... fix the issue causing overload and replace with 7.5 amp.

BTW the 15a home circuit is a bit undersize for running the air conditioner. It may work most of the time but anything extra will open the breaker. Still may experience nuisance tripping periodically. No do not install a 20 amp breaker without increasing the wire size.

On Edit: Actually you did not post the breaker size that tripped....

I think 15 amp fuse. would be correct for your AC
the 7.5 is probably what your AC draws you are ok
My class a has a 20 amp fuse and draws 12 when running

'7.5 ac', what does that mean?

The fuse panel you are showing is the 12VDC FUSE PANEL.

Your Air COnditioner is operated from 120VAC and will have a CIRCUIT BREAKER in the Power Distribution panel controlling it. You will see the 120VAC Circuit breakers to the left of your photo shown here.

The only requirement for the 12VDC with the Air Conditioner is to power up the thermostat...

bsmith image

If you are plugged into a 15-AMP Receptacle in the house/garage using an extension cord and RV Adapter then your RV air condition can trip your house 15A breaker during heavy use. You may have other items in the house also using power from the same 120VAC circuit breaker zone.

My house was wired with 12gauge electrical wiring and I have a separate 20AMP Circuit breaker that was installed for a compressor unit in the garage. This is the only thing on the 20AMP Circuit. I use this for my RV connection using a RV LONG Adapter cord.

In you case I would find a 15A Circuit breaker zone that doesn't have any other appliances or lights on the same circuit if possible. The garage is always a good place to plug in and usually it only has a few lights and a couple of 120VAC receptacles scattered around the wall. Just keep the lights OFF and make sure nothing is plugged in to any of the garage recepacles...

Just my thoughts here...
Roy Ken

See response at other forum where you posted question......:B

The other guys are all right :)

The little Buss fuse is a 12v fuse. Your AC should be on a dedicated 20 amp breaker in the Rv's load panel, and you should be plugged into a 20 amp circuit in your house.

Many RV air conditioners use both 120vac and 12VDC

The 120VAC will come off a breaker, Generally a 20 amp breaker, in the main 120 volt power distribution panel.

The DC off the fuse panel.. and yes, 7.5 may be proper.. I doubt the 15 amp fuse will cause a problem but you mignt try a 7.5.. Actuall load on that circuit should only be 1-4 amps or less depending on one or two A/C's and on or off.

The 7.5 amp fuse may NOT be the only appliance that fuse supplies. The RVP(Coleman) wall tstats have a fuse protection on the tstat(usually 5 amp or 3 amp). Dometic AC units the fuse is in the upper control board (3 amp). So, that feed 7.5 amp fuse, I would put a 7.5 amp in it. IF it blows, find out what other 12 volt items are also dead, not just the AC unit. OR, pull the fuse and check to see what 12 volt appliances/lights have NO 12 volt power other than the Roof AC tstat system. Then determine if you need a higher amp fuse. Doug