YES the DM2652 Model does have a 'Climate Control Switch'
Open freezer door and it should be approx. mid section upper trim.
Provided it is a DM2652
Have you had the batteries load tested? They may not be holding a charge.
Did you check the converter DC output.....it may not be charging batteries fully? Check with batteries disconnected....AC power in, converter output should be 13.6V DC. If not converter (charger circuit) not functioning properly?
Do Batteries have a 'disconnect switch'...if OFF batteries will not charge.