This is a typically a good opportunity to do some kegerator deep cleaning and maintenance. It seems that even with preventative measures, I need to do this rust repair about every 2 years. I believe I've had this kegerator since 2002 or 2003 and this is the 3rd time I've refinished the interior of the chest freezer. We moved the kegerator to my back yard and I started with some general cleaning using a slightly soapy towel.
After a good cleaning, I sanded all of the rust areas. This round, I had a palm sander and that made for a speedy sanding! I used 60 grit and that seemed to do the job very well. I finished with 220 to smooth out the surface before washing again to remove all of the debris.
How do I prevent rust from building up inside my chest freezer?
Moisture in the liquid form is mainly why this happens. Keeping your kegerator dry inside is challenging but using a dessicator in the form of silica gel seems to work well. I use Hydrosorbent Dehumidifiers and I'm considering upgrading to one with a larger capacity. Using a dehumidifier along with making sure your chest freezers stays closed and sealed seems to be the only preventative measures from pitting and rusting.
Reposted from 3/20/08:
A while ago, I started using desiccators to reduce the moisture in the kegerator. This has really helped slow the process and keeps the kegerator relatively dry. The greatest collection of moisture happens when I warm the kegerator up to lager fermentation temperature (50-56 degrees F). When I first started lagering, this is when I noticed a huge increase in oxidation. Last year, I sealed the drain hole for the drip tray to reduce incoming moisture and added a second desiccator.
Though the desiccators are really effective, I need to remember to recharge them frequently. This is easily done by removing the bag of silica gel and placing it in the oven at 240'F for 3 hours. On the bottom of the box is an indicator that will turn pink when the bag is saturated. After recharging the silica gel bag, the indicator gradually turns back to blue. Below is the two silica gel bags in the oven. 24 hours after placing the recharged desiccators back in the kegerator, the interior is bone dry.