97 QX4 heat comes & goes - sunload sensor?

[NismoPick]

Hi all,

Last week I picked up a 97 QX4 w/ 140k miles. Outside temp is about 35*F (I'm in Utah), but the thermometer / compass pod temp jumps around from 30*F to 131*F then shows ---. I performed the ambient sensor ohm test outlined in the FSM and it is working fine (ohms change when I dip it in warm / cold water). Harness checked & appears ok.

With the auto climate temp set to 85*F the heat output will come & go (blows hot for a min, then just warm, back to hot, warm). Fan speed stays where I put it, coolant level is full & burped (checked 3 times). I ran the auto climate control self diagnosis test & it blinks 25 (sunload sensor). So I pulled the sunload sensor & did a voltage check under full sun. It only put out about 0.5v (should be 3-5v), so it needs to be replaced, but before I go blow ~$70 on a new sensor, has anyone else had this happen because of the sunload sensor? Going through the diagnostic steps in the FSM, it seems that the sunload sensor would have minimal effect on the output temp? Would it also make the thermometer temp go crazy?

Thanks!

[NismoPick]

So I replaced the sunload sensor with a working junkyard one. No more error code 25, and no change with the auto climate control. Still blows "warm" air even though it was 40*F outside this morning. Both sides of the heater core hoses were hot.

I also replaced the compass / thermometer pod ambient temp sensor... then compared that temp to the auto climate control temp, compared to outside temp with infrared thermometer. All 3 were dead on. Drove the car a few miles. After 2-3 min, the thermometer jumped from 45*F to 56*, 79*, 131*, then ---. The FSM states as temp goes up, resistance goes down, so I can't imagine it's a break in the wire, or corrosion (which would increase resistance).

I'm leaning towards a faulty compass pod. And apparently I need to check / adjust the air mix door actuator for hot air...

Anyone... Anyone... ?

[Towncivilian]

Is this relevant, perhaps? post6285294.html#p6285294

[NismoPick]

Ok... I'm just about to slitting wrists here!

The heat still comes and goes. I have removed the stereo and watched the air mix door rod move up and down as I change the temp. Everything is working normal. My thermostat is not opening, so the lower rad hose is always cold. I've driven it hard on the freeway, up long hills, idle, city drives... it never opens. So today I pulled the thermostat, did a complete flush, and tested the thermostat and a new one (both 170*) in a pot of boiling water. They both opened at the same time at about 175*. Reinstalled everything, long 40mi drive, no change.

So my engine isn't getting up to temp, ever... WTF?

[Slumpert]

The more I read and more people describe whats going on with thier pathfinders, the more I believe the 3.3 engine is very much cooled just by the fan blowing on the engne block.

The heater core gets coolant flow regardless of the coolant temperature "provided it is not clogged" or the valve is not closed..

I have not tried any home garage test on the heater core system yet, but I would try starting with a cold start, turn the heater off completely by turning the temp to max cold and then turning fan and ac off. Let it idle for 10min and then check the heater core hoses in the engine bay. Are they both ice cold, one warm + one cold, both warm.. Then turn the heater on max and immediately check both hoses to see what changed.

Well a partial internal short could be resonsible for the jumping temperature, most likely that would be inside the pod though with a failing solder joint my fist guess. I don't think the compass pod has anything to do with the actual cooling system though, it has its own sensor when I checked.

[NismoPick]

Well I'm back to this problem again...

It's about 30*F outside today, the engine up to operating temp, both sides of the heater core lines read ~130*F with an infrared thermometer. The climate control set to 85*F full fan, and the output air is "WARM" (about 90*F when I put the infrared thermometer to the vent... it should be much hotter than that). I've done all the actuator / climate control tests in the FSM... everything checks out normal. Coolant level is normal, system burped several times (never any air). The cabin air temp sensor at the drivers knee looked dusty... blew clean w/ compressed air. NO CHANGE. My wife daily drives the QX4 with my 3 year old so and they were both cold all the way home. I need to get this fixed.

Anyone ever had this happen? I'm not looking forward to a $150 trip to Nissan to have them say "I dunno what to tell you".

[Towncivilian]

You can try flushing the heater core with a garden hose from both ends. Even though coolant lines are hot, it still may have some obstruction.

[NismoPick]

Will do. From all this research, it's seeming to be purely a heater core problem.

[NismoPick]

Back flushing the heater core seems to have done the trick. It now blows ~125*F heat. I used house water with a sprayer nozzle. From other internet posts, I was expecting tons of gunk to come out, but it was just dirty coolant... I guess enough sediment to impede the flow. Some people say to go to the local car wash and use the ~1000psi spray gun, but I wasn't about to risk an under dash coolant exposion. Thanks Towncivilian.