Step 4. Repair of the bellows. If the unit failed the leak down test, then either repair/solder or replace the bellows portion if you're lucky enough to find one. Some nice methods to find pesky leaky areas are 1) fill the bellows unit with regular isopropyl alcohol and look for weeping on the outside edges (Photo 7). Photo 8 shows another method using a bright light. Clean the suspect area, apply a coating of solder and repeat the inspection process.
Photo 7 — Concept illustration of using isopropyl alcohol filled into the bellows to pin point the leak source .
Photo 8 — Concept illustration of another method used by the author to find leaks uses a bright light inside the bellows chamber. Turned up side down and with a dark cloth or perhaps a small sheet of Luan plywood in a dark room, the leak source should be visible.
Step 5. Reassemble the Sylphon Thermostat. Resolder the repaired bellows portion into the housing base if a repair was performed. Allow to fully cool before proceeding to the next step.-
Step 6. Fill the Sylphon thermostat with two or three ounces of Methyl Alcohol (Photo 9) using a small syringe (from a hobby shop) and immerse the housing and bellows into a bath of ice water to lower the boiling point of the Methyl Alcohol (Photo 10). Solder shut using a high wattage electric soldering iron. Never try to use an open flame heat source as some alcohol may escape through the hole and may catch fire. The ice water minimizes this effect, but not entirely.
Photo 9 — Methyl Alcohol is available from scientific and chemist suppliers and small syringes are quite common in the paint or glue department at your local Hobby Shops.
Photo 10 — The housing and bellows unit is immersed in ice water to lower the temperature of the Methyl Alcohol while the housing is soldered. While this picture shows a shallow bowl, a large coffee can proved to most successful. Soldering must be performed using a heavy duty high wattage electric soldering iron. An open flame should be avoided as some alcohol may escape and catch fire.