You won't know until you connect the pipes back up to it(or rip it out and replace it) they may have bypassed it in ignorance because it wasn't working but it may well have only been air locked(they don't usually fail).You have nothing to loose by connecting it and trying it,at worst you will get a wet floor and that will dry.Connect a pipe to the top tube where it comes out of the bulkhead run water through it then get someone to put their finger over the bottom tube where the water should be coming out and look for leaks in the cab,make sure the heater controls are on max,doesn't matter about the fan(ignition off anyway)if you have no leaks I would connect it up,may leak under pressure but eliminate the obvious and easy options first.Good luck.
Rich
January 2010
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