2015 Nissan Sentra Blower stuck on high

Michael from Holt Diagnostician Posted   Latest  
Question
HVAC
2015 Nissan Sentra S 1.8L (MRA8DE) (RE0F11A)
Blower Stuck On High

Ok question for those that may be more familiar with Nissans Hvac system. I have a 2015 Nissan Sentra that I have tested by the trouble tree from Identifix and Mitchell and tested powers and grounds to the modules. Problem came in blowers not working and quickly found the two fuses missing. 

I replaced the missing fuses and found that the blower never shuts off with key on. So pulled a wiring diagram and started checking the signals to the Variable speed blower control and the A/C Amplifier. Found that the Pwm and the on signal too the bcm never changed. These signals come from the amplifier. The blower motor speed signal from main controller comes over to the A/C Amplifier via Uart network between the two and does not have any other network attached. 

I can unplug the switch controller completely and it still runs. This is a manual hvac system not the automatic version. We ordered dealer parts for the A/C Amplifier and the Variable speed Blower control and same outcome blower stuck on. In bcm data under Ac the switch reads on all the time which it receives that signal from the A/C Amplifier which never seems to change when scoping it either. I know I have to be overlooking something and figured I would ask you here for your input. Going to rescope in the morning as it seems the pwm to the Variable speed blower control did in fact improve but still dont change when switch is moved around. The improvement was in the amplitude of the signal generated. Any ideas are appreciated 

0

Robby from New Market

 

Mobile Technician
 

Hi Michael, I do have a couple of thoughts:

  • Does the blower motor still work with the speed controller unplugged? 
  • What voltage did you have on the PWM signal?

Can you post the waveform from the PWM speed control signal?

From what I can gather out of SI, the blower motor input signal to the BCM is for compressor control.

+1 Ð Bounty Awarded

Geoff from Lahaina

 

Diagnostician
 

Agreeing with last sentence there. The IPDM (through the network) wants to know that the blower fan is moving or it will not energize the compressor.

Not that it helps solve this problem, but every blower complaint I have seen that "made no sense" was on a Nissan. I am convinced they leave something out of the diagrams.

I look forward to this going somewhere good.

0 Ð Bounty Awarded

Michael from Holt

 

Diagnostician
 

Yes still works with controller unhooked and will have to hook up the pico as I was using the vantage pro at the time. The pwm does not look normal but will capture some today and post them. Thanks

0 Ð Bounty Awarded

Michael from Holt

 

Diagnostician
 

Thank you for your input and them were my thoughts as well. This car is now fixed it ended up being the controller. Gonna try rescoping the UART signals and see what has changed on them. I found it odd they never changed with moving the switch so I will gather new signals and compare to old signals and hopefully can find a way to post them off the Vantage Pro. 

+1 Ð Bounty Awarded

Geoff from Lahaina

 

Diagnostician
 

You said you already replaced the "A/C Amplifier and the Variable speed Blower control". What are you now calling a "controller" Mike?

0 Ð Bounty Awarded

Michael from Holt

 

Diagnostician
 

Its the control head that contains the blower speed switch itself. It talks via Uart no actual signal wire just the comm wires to Amplifier 

0 Ð Bounty Awarded

Geoff from Lahaina

 

Diagnostician
 

so would that be what the wiring diagram calls the "A/C Switch Assembly" ? Thank you

+1 Ð Bounty Awarded

Michael from Holt

 

Diagnostician
 

Yes exactly I guess I probably should use the correct terms thats my fault. This was for sure a learning experience on this system and now I have known goods for future use

+1 Ð Bounty Awarded

Geoff from Lahaina

 

Diagnostician
 

That'd be a great video. Showing the signal changes between Amp and Switch for the various blower speeds

0 Ð Bounty Awarded

Adrean from Bakersfield

 

Diagnostician
 

I had one with a similar problem . Through the diagnosis I found the signal always coming from the amplifier . I was ready to call an amplifier as faulty . Until I found out they replaced the dash . . After this i found out they replaced it from a vehicle with auto a/c not manual . And they switched the amplifier accidentllly . Found the old amp . Switched it and all good 

0 Ð Bounty Awarded

Adrean from Bakersfield

 

Diagnostician
 

The h6 one was the auto . And the m1 was manual 

+1 Ð Bounty Awarded