A while back my AC started to cut out intermittently. Usually letting the car sit for a few hours or overnight would enable me to have AC again. Sent it to the dealer in Orlando and they had no idea what was going on (took them over a month to determine this). Moved to Boston and the heat completely died in mid-March. Got a new blower motor but it wouldn't turn on. Went back and forth between mechanics and no one had any idea what was going on.

Sent it to the dealer up here. They made the very kind offer of a $1,000 diagnostic fee to remove the dash. I passed on this very generous offer. Local mechanic suggested I change out the Audio Control Unit (thing under the screen with the buttons for air, map, phone etc.). I swapped it out and still nothing - the blower motor still will not engage (we have tried two brand new blower motors btw.).

It's now in the low 20's and the seat heater only does so much. My mechanic mentioned the ground to the blower motor is pulsing but can't figure out why. I ran the "secret diagnostic" test and was greeted with this message: "self diagnosis could not run because of a control unit malfunction"

Any and all help is appreciated. It's a 2006 M45 Sport

I was going to ask if the blower motor turns on but looks like that's part of the problem. Did you check all the fuses/relays including the ones in the engine bay, etc.? You'd think mechanics would check that stuff but just doing our due diligence here...

Sounds like a bad HVAC blower relay...Conveniently located behind the fuse block in the driver’s foot well.

Mine started as intermittent lack of heat, but would assume that it would progress to a full failure (as you described).

For $20, worth trying that fix, before you go down a more complicate (expensive) path.

Here is the one I used to replace the bad one, several years ago...
Genuine Nissan 25230-79942 Blower Motor Relay https://www.amazon.com/dp/B00BFE4ZI8/re ... oCbT9EQY39

Ilya wrote: ↑

Sat Jan 12, 2019 5:52 pm

I was going to ask if the blower motor turns on but looks like that's part of the problem. Did you check all the fuses/relays including the ones in the engine bay, etc.? You'd think mechanics would check that stuff but just doing our due diligence here...

The mechanics and dealership claimed to have checked these. I believe the mechanics did check them. The dealer, I dont trust much

ae7456t wrote: ↑

Sat Jan 12, 2019 6:04 pm

Sounds like a bad HVAC blower relay...Conveniently located behind the fuse block in the driver’s foot well.

Mine started as intermittent lack of heat, but would assume that it would progress to a full failure (as you described).

For $20, worth trying that fix, before you go down a more complicate (expensive) path.

Here is the one I used to replace the bad one, several years ago...
Genuine Nissan 25230-79942 Blower Motor Relay https://www.amazon.com/dp/B00BFE4ZI8/re ... oCbT9EQY39

Much obliged. I will pick one up

I just got a 2010 m35. I live in south fl, it's a lil chilly this week and I wanted some heat. I turned the temp to 81 but nothing was blowing out the vents. Could the relay be the culprit also?The ac works ok, to me it could be colder. Will need it for when the summer rolls around.

My symptom was similar to what you described...It would be cold outside, I would set the heat to warm things up, the car would warm up, but no heat would be blowing out of the vents. I think the dash display even showed that the fan had ramped up to blow the warm air, it was just not happening. Eventually, if I drove long enough, it would start to blow, but it took 15+ minutes to get to that point...I assume that, if I waited long enough, it would have quit altogether, but I live in a cold climate, so I replaced the relay before I got to that point...No problems, since.