I just traded my 7753 for a 2001 T190. It has heat & A/C, enclosed cab, etc. The heater didn't work weel when I got it, and I think I have narrowed it down to the one problem. The electric valve that shuts off the coolant flow isn't working too good, so I took it off and turned the valve myself. There is a 'T' in the lines going to the heater core, so when the valve is off, the coolant just recirculates. I think the problem is that the coolant just flows through the 'T' instead of going all the way back the core. As they say, the passage of least resistance. So, my question is - the short hose that connects the 'T' together is the same size hose as the rest of them. Shouldn't the hose be smaller or there be some kind of restrictor in it, so when the coolant valve is open, the passage of least resistance is through the heater core instead of the 'T'? Otherwise the coolant barley passes through the core, and there is no heat in the cab? Anybody have any thoughts? Thanks!!