I have a 96 maxima. I have done the following: Thermostat changed, water pump changed, heater core changed, resistor changed, regulator changed, system bleed and still not heat....why? What could I possible need to do next?!

 

OEM parts, or aftermarket? Standard or Auto Climate Control? Sounds like you covered all the bases, but I'll reiterate and add a couple tips.

You need to first determine whether the heater core is filling up with hot coolant that can transfer all that heat to your feet. This is easy. Simply wait until you are driving at a good speed - I'd say 40 mph or faster, and switch the controls to heat. If you feel heat coming through any of your vents, even a tiny trickle of heat, then your heater core is likely getting hot coolant. If you feel that trickle, you are probably having a problem with your heater fan. Check your controls and try it on different fan speeds to see if you just have a dead speed. Still nothing? Check your fuses to be sure it's not that.

If you don't feel that trickle of heat, your heater core is not being included in the circulation of hot coolant when the engine is warmed up. First, check your coolant level to be sure there is enough coolant in there to even get to your heater core. If your radiator is very low on coolant, you'll get no heat. If your levels are ok, you either have a bad water pump or a thermostat that isn't opening. If your car has not been overheating or running hot, your water pump is not the culprit. Even though you replace the thermostat, it could still be faulty. The thermostat opens and closes circuits in the cooling systems as the engine heats up. If a thermostat is stuck in the closed position, it will never allow coolant to circulate fully, so no heat for you.

And lastly, maybe it's your air mix door that's causing the problem.

 

coolant levels are good
i'm pretty sure coolant is running through heater core because I had not secured a screw when first installed heater core and coolant was spewing everywhere. tighten screw and no more spewing. How do I tell if the new thermostat installed is faulty?

 

After you've driven the car around and everthing is nice and hot, your fans have kicked on etc, feel both radiator hoses. They should feel the same. If one is hot and the other is cold (thermostat side), you've got a bad thermostat.

You didn't answer my other questions. If you don't answer, we can't eliminate stuff.

 

coolant levels are good
i'm pretty sure coolant is running through heater core because I had not secured a screw when first installed heater core and coolant was spewing everywhere. tighten screw and no more spewing. How do I tell if the new thermostat installed is faulty? Where is air mix door?

 

both hoses get hot, standard heat control, fans kick on as required

 

all fan speeds work? OEM or aftermarket parts?

 

When fan is running, it is running in all 4 speeds? Do you feel any air coming out of vents?

 

It is possible that the door that diverts air to the heater core, is not working.

 

I second this one. The dodge omnis (was/is into them for a while) did this crap when they got old. Check the little flapper door that controls the vents to cold and hot air.

 

OEM and yes fans work on all speeds

 

Where is that door?

 

Nissan calls it the Air Mix Door. It is completely enclosed inside the air duct work, against the firewall above the ECU. Right above the ECU is a small electric motor, the Air Mix Door Motor, that moves the door.

What you need to do is get down in the passenger side footwell and remove the plastic cover that hides the ECU. Then look above the ECU for the arm that connects the motor and the door.

Turn the ignition switch on (you don't have to start the car) and change the temperature setting in the heater control panel. If things are OK, you will see the arm move.

 

The arm moved just fine when changed from air, floor, to defrost but not when changed temp.
Can you tell me what this part bbq is, please?

 

I think that is the Mode Door Motor. The Mode Door Motor switches which outlets the air come out from (floor, dash vents, defroster, etc). The Mode Door Motor has nothing to do with the temperature of the air. Where is this motor mounted? Is it from the driver footwell side about as high as the radio?

The Air Mix Door Motor that I posted the photo of will move when you change the temperature. It does not move when you change the air outlets.

MODE DOOR MOTOR

 

OK, then I must have seen the wrong motor. I will look again this afternoon.
Yes, that motor is exactly where you stated.

 

If both hoses attached to the heater core get equally hot, your heater core is being fed.

Blend door actuator is the most likely candidate at this stage.

And you're already on it, so this will be put to bed just in time for the rest of the WINTER! YIKES!

Good luck!

 

feel the heater hoses @ the firewall! Are they hot? Is there coolant flowing thru the heater core hoses? Ok I see you did this already! So that tells us it's inside the climate control section maybe mixing in too much cold air! Make sure the fans are blowing and not sucking!