Coolant circulation

[JeepSJ]

While I am on the topic of fluid circulation through the engine, I have a question about coolant going to the heater core.

From what I can see, hot coolant is picked up from the t-stat crossover, routed through the heater core, then back into the water pump (or the cold tank on the radiator, depending on year/application). Question - does that coolant circulate through the heater core all the time, and is that part of the bypass circuit when the thermostat is closed? I need to know because the heat/air-cond unit that I want to use has a valve that stops the coolant from going through the heater core when the heat is off. I know there is a bypass hose that goes from the t-stat housing to the water pump - is that the only bypass that the system needs?

Thanks!

[HammerWerf]

Jeep

On my 83 & 84, the coolant flows through the heater core all the time. The flow returns to the radiator just above the oil cooler Hx to help warm and stabilize the oil temp. Did have a heater core leak a couple of summers ago. Connected the end of the hoses to each other, and the A/C cooled the cab a lot better.

Not sure about the '99. I did note a couple of summers ago that if the temp select dial was ONE click above cold, the heater added heat to the A/C, making for a warmer ride in the California Central Valley heat.

Hope this helps.

HammerWerf