Your Nissan Quest comes equipped with two heater cores as part of the front and rear auxiliary systems to conveniently provide heat to the whole area of the minivan passenger compartment. Eventually, the heater cores may rust, clog, develop coolant leaks and provide little or no warm air. Fortunately, you can remove one or both units without the need to disassemble whole panel sections for heater core service.
If you plan to reuse the coolant mixture in your system, drain the coolant into a clean container and put a lid on it until you are ready to use it. Then you are ready to work on the heater core. First, working from the engine compartment, disconnect the two heater hoses form the heater core tube. Then from inside your Quest cabin, remove the heater unit air ducts and the heater retaining bolts.
Look behind the door motors and unplug the electrical connectors. Then you can remove the heater assembly and detach the heater pipe cover plate, the heater core retainer and heater core shutoff-valve control rod.
Now the heater core should be visible and easy to remove from the heater unit.
Rear Auxiliary System
The second, rear heater unit on your Quest model is located behind the driver-side rear panel. Before you remove it, though, take your vehicle to an approved facility and have them discharge the air conditioning system refrigerant. Then drain the cooling system into a clean container, if you plan to reuse it. Then disconnect the hoses from the rear auxiliary heater core tubes.
In order to access the rear heater and air conditioning housing, you need to remove the driver’s side rear trim panel. Once removed, you can detach the rear A/C system upper and outer housing. Removing the upper and outer housing gives you access to the evaporator and heater core assemblies. The heater core is the one on your right hand side or the one located nearest to the upper housing.