Some people will say this is crazy. Some of the biggest Factory Authorized machine service centers in the country regularly use this method to clean machines before servicing & repair.
In the event a welding machine is very dirty inside, possibly impeding performance, before heavy repair it can be successfully power washed with MODERATE water pressure. About 1500-1800 MAX is fine. Steam is great too, just use caution to avoid internal damage to your machine being sprayed by excessive temperatures & or pressures. Using excessive pressures will destroy components inside the machine in a big hurry! In the pictures below, the machines washed were done in steps. First, the friable dirt is removed by brushing & scraping. A vacuum can also be used to evacuate the dirt from inside the machine. In some cases, an oily film is present & should be scraped as best as possible before power washing. Before power washing, it is advisable to remove any circuit boards. These can be cleaned in the kitchen sink with warm water & a mild detergent. Drying is accomplished with moderate pressure compressed air.
It is best to pre wash the machine, then apply a moderate degreaser, such as "Mean Green" or "Greased Lightning" brand with a trigger sprayer. Stubborn areas can be cleaned with a brush. After washing, block the machine up on one side, or slightly invert it on a dolly, as below, to run off any excess water. After the water drains off, I use a moderate amount of compressed air to evacuate any standing water inside coils or other areas. Since most shops do not have a "dry room" to dry machines using heat & forced air, box fans can accomplish the same purpose, as shown below. You can see I place one on each side & cover the top of the unit to promote air circulation. Drying time depends on the ambient temperature, but about a day is sufficient in most cases. If you do not have a pressure washer, the car wash will do fine. Be aware that some automotive soaps are corrosive & should be used with care.
After drying, re spray the components inside with compressed air to insure complete absence of water. Perform any & all factory outlined pre-power checks before applying input power.