Hi first you shouldn't be getting any frosting on components at all this usually points to either a leak of if its the vaporiser a cooling fault. First thing to check is that coolant is getting too and passing through the vaporiser if it isn't the vaporiser will frost over then freeze up if this is happening this will give the problem you have ive had water pump impellors fail that give this fault. I don't know if you can buy kits over there for the J type impco but if you do stip it there is a strip valve with a rubber seal in the middle these are prone to failure and you wont get it to start if it is they fail due to the body wearing where poppet that works on the hp diaphragm wears. My advice if you cant get a repair kit would be to fit an imcpo k type to it.