Diagnosing Nissan HVAC Issue

[The_Nuke]

I have plans to help a coworker try to figure out what is going on with his car's A/C, but I have no experience working on late 2000's Nissans, so I figured I would see if anyone has some tips and tricks that I need to be aware of.

The car is a 2007 Nissan Altima (base model) w/ ~ 120K miles

The problem is that upon entering car and starting the engine, it can take several minutes before the A/C starts to actually blow air out of the vents. It is not every time that this happens, but it does happen often enough, and it is hot enough here now, that it's become a real problem for him. And he knows as much about working on cars as I know about flying passenger jets, so I figured I could try to help him figure out what's wrong (or at the very least rule out some things as being the cause).

I did a cursory exam on it myself, and I see that it does not matter what the desired temp is or where it is set to blow air from. Cold or hot, A/C or heater, dash or floor, the issue will happen when it decides to happen. The lights on the control panel light up in response to my inputs on air speed, temp, etc., but there is no noise or air flow at all for a minute or two after starting the engine and commanding it to blow.

Previously he stated that once it did start to blow air, it would remain responsive to driver inputs the duration of the trip until engine shutdown. But just yesterday he stated the air started to shut off and restart itself during the middle of his drive. So whatever is wrong is getting worse it sounds like.

I have asked him to get a Chilton's manual to help lay out how to access the various HVAC components behind the dash, but I am not overly optimistic that it will be a huge help. I have noticed a downturn in their usefulness lately, with some editions being too generic to be of much help. So if anyone has some hints, tips, or tricks to pass along, they will be much appreciated.

Also, I figure the electronic control module that commands the blower motor is the best place to start. Hopefully I can test the output voltage it sends to the blower motor in response to commanded inputs. If that proves good (or I cannot sufficiently test it), I figure the actual blower motor itself would be the next suspect to rule out. I checked the underhood fuse box for the presence of a relay that controls the blower or A/C functionality, but I did not see one listed on the underside of the lid. There is an A/C fuse, but that is not blown or anything. What else can we look at as a possible suspect?

thanks,
nuke

 

[joel95ex]

Going to have to troubleshoot individual items. first the control panel. many have a built-in diagnostic mode that will run through all of the location (floor, dash, defrost) and then flash a code. then you'll need to see if the blower fan is going bad. While a blower fan or resister is fairly cheap, the problems with some nissans is the location of the fan. I have seen some nissans where the fan is right in the middle and requires the gas pedal to be removed for access. if those things are working, then its time to see if its cooling. check to see that compressor is engaging and then if the system is charged.. try to avoid topping off with refrigerant, as these systems are easy to overcharge. it really takes a full AC gauge set to see whats going on with the high and low sides to know if if the compressor is bad or if the expansion valve is bad vs just a low charge.

 

[28oz]

Don't know about in Texas, but here in Utah there is a chain repair place called Tunex that does free A/C diagnoses. I've used them several times to diagnose and/or repair depending on what the issue was. Might be worth some calls around to different shops in your area? Sometimes even paying a diagnosis fee is worth not having to guess or spend a ton of time trying to find the issue yourself. Just a thought.

 

[VeryNoisyPoet]

Checking voltage at the blower motor is a good place to start. Could be failing fan speed control. On my dad's old car the fan would glitch out like that where it would not blow air but then begin working again. Or it would bog down in the middle of a drive even with the speed selector turned up.

If there's good voltage with the speed control at max but the fan refuses to turn, tap the motor gently with a small hammer to see if it begins working.

 

[WhyMe]

Common thing on many cars is the fan resitor going wonky . cheap swap

https://www.carparts.com/details/Nissan/...mp;gclsrc=aw.ds

https://www.ebay.com/p/HVAC-Blower-Motor...5969&chn=ps

 

[The_Nuke]

Originally Posted By: WhyMe
Common thing on many cars is the fan resitor going wonky . cheap swap

https://www.carparts.com/details/Nissan/...mp;gclsrc=aw.ds

https://www.ebay.com/p/HVAC-Blower-Motor...5969&chn=ps


The behavior struck me as the type exhibited by a failing resistor, but in my limited research online, I gathered that this car didn’t have a resistor for the fan due to its type of fan speed control - gradual electrical selection as opposed to switched 4 or 5 distinct landing spots. That’s another thing I hope the Chiltons manual can clear up.

It would be nice if the fix were as straightforward as replacing a part like this. We’ll see...

 

[Chris142]

Look into the evaporator temperature sensor

 

[The_Nuke]

Originally Posted By: Chris142
Look into the evaporator temperature sensor


The behavior persists whether or not A/C has been selected. A/C can be off, temp can be max hot, and vent can be floor and the behavior doesn’t change (usually several minutes before air blows, but not always). Wouldn’t a malfunctioning ETS limit its effects to A/C operation only?

 

[clinebarger]

Nissan is terrible about supplying good diagnostic information.....
Cell diagrams....Terrible
Component Control theory....Non-existent
Diagnostic Flow Charts....Well, They are written by engineers that try to dumb it down for mediocre automotive technicians. Those charts will have you running around in circles unplugging connectors to check voltages & OHM'ing circuits for 2 days!

It appears the the Blower Motor speed control module is built into the blower motor itself. As you can see in the diagram....
*The motor has a permanent ground
*12VDC is supplied by the blower motor relay
*The HVAC control head sends out a "Signal" to control blower motor speed, If I were to guess.....A D/C square wave (5 or 12VDC) that's applied in a "Duty Cycle".

First thing I would do the next time the motor won't start is give it a few taps with a 3/8" drive extension....Not on the module, More toward the Motor/Brushes.

 

[The_Nuke]

Thanks for the info, I will save it off in case we need it. But for now, it appears as though the problem has been resolved. I did some more digging around and found a thread on an Altima forum in which the very same symptoms were discussed, and which several of the folks had fixed by replacing the blower motor relay.

I had searched for one of those in the underhood fuse box and didn't find one, so I was a little surprised to hear there was one at all. Turns out, it is on the backside of the interior fuse panel (who does that?!?!), along with several others of the same size/type.

Long story short, after spending way too much time and effort to get to the relays on the backside of that fuse panel, I swapped out the blower motor relay with the radio relay next to it, and that did the trick...at least for now. We'll see if the fix holds.