Does coolant pass through the heater core and its o-rings if the HVAC system is set to a temperature that’s not ‘hot’? To clarify: does coolant always passing through the heater core - whether or not the HVAC system is engaged - or is the heater core automatically bypassed when hot air is not being requested? If the heater core is automatically bypassed, at what temperature setting is it bypassed or does the temperature at which it’s bypassed depend on the temperature outside? If the heater core is not automatically bypassed, can someone please direct me to instructions on how to manually bypass it? Thanks!