I’ll assume that your machine is 3 phase, 208 (or 480) and has a step-down transformer to 120v. The 120 is used to power all control devices (contactors, solenoid valves, gas heat controls, etc.). That 3.2a amp fuse is there to protect the transformer in the event of a short circuit somewhere in the 120v circuit.
I take it the machine is already full of water…which would explain why 5CR is trying to energize so soon?
From what I see in the schematics from that old manual, 5CR energizes after the left tank’s lower float switch (the 4 wire one) closes, then 5CR’s contacts close to power the left tank’s igniter board.
Anyway, you obviously have a short somewhere in the 120v circuit. 5CR is an ice cube relay. It may be arcing simply due to its contacts being pitted. Arcing contacts won’t blow a fuse. However, I recommend you address that first by checking the circuit it energizes using an ohmmeter.
From my own experiences, that fuse blows due to a shorted solenoid valve or contactor coil, a shorted float switch (rare), a shorted door switch…or a wire somewhere that has rubbed out to ground.
The FIRST thing you should do is a VERY thorough visual inspection of all components and visible wiring. I’m sure you already know what you’re looking for.
If you find nothing burnt, chafed, deformed, gotten wet, etc. – then you can proceed by going about this in two ways:
1. Remove power from the machine, then use your ohmmeter to go through all the individual 120v circuits branches to find any unusually low resistance paths (or continuity). Do so using some logic by knowing what should get energized WHEN. So, what get energized just by turning the unit on, then what gets energized after certain processes have completed (e.g., tank must fill to a certain level before heating, etc.).
2. Another way to troubleshoot for a short circuit is by doing what I call “trial by fuse”. YES, you should be equipped with numerous spare fuses. THEN, disconnect ALL components, power the unit up, then CAREFULLY, slowly and meticulously reconnect stuff ONE AT A TIME…until your sacrificial fuse blows. Obviously whatever you reconnected LAST will lead you to where the short is at.