This issue has been covered in other posts before yet the ones I relied on in the NICO forum are at least 3 years or older so I thought I would renew the content for anyone who is looking for a solution. What I detail below solved my issue completely.

CAR: 2007 Infiniti M35x, 243,000 km (~ 150,000 miles)

PROBLEM: Defroster/heater does not work at cold temperatures. It generates heat yet the heat isn't distributed because the blower doesn't turn on. Temperatures below freezing (0C / 32F) would cause the blower to become intermittent. Above freezing there was little to no lag in terms of responsiveness.

DETAILS: The blower motor for the defroster/heater becomes less reliable as the temperature gets colder. The issue was inconvenient at first (i.e. would only work after engine was at temp), then problematic (i.e. colder it was longer it would take to come on if at all), and eventually the defroster/heater were non-functional at temperatures below 0C / 32F. This made it so that parking/storing the car outside or in an unheated garage meant the defroster/heater would be non-functional on cold days. I took the car to my mechanic (non-dealership) twice and he failed to identify the relay as the problem. In retrospect, I believe that is because he tested the relay at room temperature which, under those conditions, it would perform as expected. The next round of diagnosis/possible repairs were likely to be very expensive (i.e. ripping out the dashboard and replacing secondary HVAC units behind the stereo) so I held off on these work items and did a little research on the Internet. Through the NICO forums (and others) I discovered that the Blower Motor Relay was commonly a source this problem with Infinitis and Nissans alike.

SOLUTION: Replace Blower Motor Relay (part no. 25230-79942)

CORRECTIVE ACTIONS:
1. Bought Blower Motor Relay on eBay.

-- after part was delivered --
2. Move the driver's side seat back as far as possible.
3. Disconnect negative terminal on battery (10 mm nut).
4. On the driver's side, open the door and remove kick plate (also called sill plate). There are three snaps located at top left, middle, and back right. If it has not been removed before may require a bit of leverage.
5. Remove the fuse box covering to the left of the emergency brake along the outer side of the footwell. Start by removing the black (10 mm) nut located at the back against the firewall then pull the panel inwards towards the pedals. There are two snaps along the door jam.
6. The relay is located on the BACK of the fusebox. To remove the fuse box from its mount you will need to remove the two (10 mm) screws at the top and use a narrow flathead screwdriver to pop the tabs at the bottom. There was only one tab in my case (which is good) and I had to apply upward pressure on it until the fuse box was moved forward enough to prevent the tab from re-engaging (locking).
7. Pull the fuse box out enough to see the back on it. You will likely have to manipulate the hood cable on the right and the power cables on the left to work it free.
8. On the back of the fuse box there are two relays. They are square and blue. The one on the left (i.e. the one closest to the firewall when the fuse box is mounted properly) is the one for the Blower Motor Relay. Gently work this relay out and replace it with the new one.
9. Reconnect the battery, start the car and test the Climate Control. If it all works turn off the car and disconnect the terminal again.
10. Put everything back together.

TOTAL TIME: About an hour or more.

TOOLS USED: Ratchet and 10 mm socket, narrow flathead screwdriver, small flashlight or lantern

** Special Thanks to Inifinit620 for original detailed post that this one was based on.

Welcome to the forum!
Exceptional 1st time post!
Looking forward to you participating in future discussions, and of course, any other fixes you come across!

Thank you for sharing this.

That's an AWESOME first post!!! Thank you!!! And welcome to NICO!

Well I've got the same issue on my 2007 M35x. I replaced the relay as per the original poster's write up and.......nothing. The A/C compressor kicks on when I engage the switch, but the fan doesn't work with either the heat or the A/C. Any other ideas why the blower motor doesn't work? Like the original poster, it used to go off intermittently - especially when it was cold outside - but would come back on after a few minutes. Now it just doesn't blow at all. Thanks.

DELETED

Your M has a pancake brushless (BLDC) motor similar to the Altima, which is pretty simple to diagnose. There's no separate VBC (resistor), so simply check power into the motor, ground out of the motor, and see if you get a voltage on the control wire that moves when you increase/decrease fan speed. To check power and ground use a bulb-type test lamp. The fat White wire should have power at all times, if not then you have a wiring problem between the relay and the blower or the relay isn't turning on. The fat Black wire should have solid ground at all times, if it lights the lamp even a tiny bit then your ground connections are bad. If that checks out, put a voltmeter (NOT a test lamp) on the skinny Blue/Yellow wire and look for a voltage that's 9V+ with the blower off and drops as you increase fan speed. If all that checks out, your blower motor is bad.

Here's your FSM, the HVAC wiring diagram starts on ATC-46:
https://www.nicoclub.com/service-manual ... %2Fatc.pdf

Well, I'm not too handy chasing down electrical shorts. I did manage to install a cool LED brake light and headlight flasher on my Honda Aero 1100 but that was several years ago. I pulled the fuses (both 15 amp) and they were fine. Did a you tube search for the blower motor replacement. Huge shout out to EdBwoy, a big contributor to this site, for posting two videos on the topic. Such an easy fix. I got a replacement (aftermarket) motor on Rock Auto and it literally took 20 mins to switch it out. Problem solved! I will say that one of the contacts on the wiring harness looked a bit burnt up so may need to replace that at some point but all is good now. As it turns out, the old motor was from the same manufacturer (TYC) and was built in 2015 so it lasted about 7 years. For less than $100 all in, I'll take that!

MM...Good wrote: ↑

Thu Mar 17, 2022 5:47 pm

As it turns out, the old motor was from the same manufacturer (TYC) and was built in 2015 so it lasted about 7 years. For less than $100 all in, I'll take that!

I fixed an '07 Altima a couple days ago that appeared to have the OE blower still in it. Lasted 15 years. Those pancake BLDC's are wonderful, I don't know why Nissan doesn't use them in everything.

VStar650CL wrote: ↑

Mon Mar 14, 2022 6:00 am

Your M has a pancake brushless (BLDC) motor similar to the Altima, which is pretty simple to diagnose. There's no separate VBC (resistor), so simply check power into the motor, ground out of the motor, and see if you get a voltage on the control wire that moves when you increase/decrease fan speed. To check power and ground use a bulb-type test lamp. The fat White wire should have power at all times, if not then you have a wiring problem between the relay and the blower or the relay isn't turning on. The fat Black wire should have solid ground at all times, if it lights the lamp even a tiny bit then your ground connections are bad. If that checks out, put a voltmeter (NOT a test lamp) on the skinny Blue/Yellow wire and look for a voltage that's 9V+ with the blower off and drops as you increase fan speed. If all that checks out, your blower motor is bad.

Here's your FSM, the HVAC wiring diagram starts on ATC-46:
https://www.nicoclub.com/service-manual ... %2Fatc.pdf

OK - my fix of replacing the motor itself was short lived. The connector looked to be burnt where the white wire was contacting so I bought used oem from Ebay and spliced it in place of the old connector. I pulled the motor from the mount and supported it on the floor and turned on the car and hvac. The motor does turn, but only slowly and does not respond to increased fan speed selected on the dash. What could prevent it from spinning faster?

The speed control on those BLDC's is built in, so either your control head is messed up or the new motor is. Put a VOM on the control wire (the smallest one) with the connector in place and see if the voltage changes when you change the fan speed. If it doesn't, do the same test with the connector detached. If it doesn't change in either condition then the A/C Auto Amp has a blown driver or there's an open in wire between the Amp and the Blower. If it changes in both conditions or if it only changes when loose, your new Blower is bad.