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Discussion Starter #1 (Edited)
Hello all. I'm a new owner of a manual 2019 PRO-4X. Liking the truck so far, but I'm trying to figure out if some quirks with the HVAC system are issues, or if they are normal for this truck.
  1. When the HVAC is turned on in ANY mode, I ALWAYS get some air flow from the side vents, even when there should not be flow there (such as when it is in floor-only mode). I'm not talking about the vents that blow on the side windows, but the side vents that are meant to blow on the driver and passenger. The center vents have no air flow in these conditions. It seems as if a vent door is not closing all the way. Is this normal? (EDIT: confirmed normal)
  2. "De-humidified" heating is a new one for me, and I'm trying to learn about how this works, but I feel like something is not working properly. As I understand it, the AC should automatically come on (even if AC button is off) when I am defogging the windows, either in full defog mode or defog/floor mode. That makes sense. However, when I turn on the heater in floor-only mode, I can still hear the hiss of the AC compressor every couple minutes or so. The compressor should not be engaged in this mode, correct? According to the manual, de-humidified floor heating should only be happening if the AC button is turned on. (EDIT: fixed by correct order of operations - mode button first, THEN fan speed dial - not vice versa)
  3. Speaking of the audible AC compressor hiss, is this normal? It's pretty loud in the cabin, very noticeable, even over moderate volume music. I've never heard this in any other car, but not sure if this is the norm for the Frontier. I doubt a brand new truck is already low on refrigerant, unless there is a leak somewhere. I can't say if the AC is working since it's so cold here now.
Thanks for any feedback. Sorry if this is in the wrong section - I didn't see one that looked like the obvious place for an HVAC discussion.

EDIT: forgot to mention a couple things:
  • I am not using AUTO HVAC mode yet - still trying to figure out the basic operation
  • I have read elsewhere and understand that once I turn on defog, the AC compressor cycles until the truck is turned off regardless of mode. I am talking about a fresh startup with HVAC off, then I turn on the heater which was in floor-only mode, and the AC is cycling under those conditions.
 

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I dont have auto-air, I have basic type 1 hvac, but nothing in your description is normal except compressor cycling which is different on the auto and its way to boring trying to read through it in the manual,first thing you need is to go to the Nico site and download the last manual they made available 2016,which is 99% same as your 2019.then check for body codes which will show if any of your hvac door actuator motors are out(i thick there's 4-5 on the auto),could be ground or BCM faults.
 

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i thought I read somewhere (on here) that you have to cycle the fan to "off" to fully disengage which ever A/C compressor mode that you were in. In other words if I select full defrost and want to shut it off I have to select another mode, turn the fan off and then back on. This allows it to fully switch to the non-compressor focused mode... Sound familiar to anyone?
 

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Discussion Starter #4
@bajasam - Thanks, I'll check out the NICO site - was wondering if service manuals were freely available anywhere.

@jfk-usaf - Yeah, I have read about that too, however, I am turning the fan off. Here is the sequence: turn heater to floor-only mode - turn HVAC completely off - turn truck off - wait a few minutes or overnight - turn truck on - turn HVAC on and it comes on in heater floor-only mode - AC compressor cycles. I am fairly certain the compressor should not be cycling in that case.
 

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@bajasam - Thanks, I'll check out the NICO site - was wondering if service manuals were freely available anywhere.

@jfk-usaf - Yeah, I have read about that too, however, I am turning the fan off. Here is the sequence: turn heater to floor-only mode - turn HVAC completely off - turn truck off - wait a few minutes or overnight - turn truck on - turn HVAC on and it comes on in heater floor-only mode - AC compressor cycles. I am fairly certain the compressor should not be cycling in that case.
I would agree. Not sure why the compressor would cycle in this scenario.
 

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Discussion Starter #6
Thanks for the feedback. I am taking the truck to the dealer next week for a different issue, but I will ask about these HVAC issues at that time and see what they say. I just wanted to check with some owners to see if I was way off base before telling the dealer something is wrong.
 

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I believe my 2018 does the same thing in any type of heat situation. It's just like you can't change to recirculate in heat mode even though it's warmer in the cabin than it is outside (fresh air). Also when you turn the system completely off it still keeps regulating the temperature setpoint that you last have it at. That's why the temperature setpoint stays on for a short time when you turn system off. Just like everything else, they are trying to take all control away from the operators and make it the way THEY think we want. Kinda wish I would have just got the one with the basic HVAC, but the other half always likes a different temp than I do.
 

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Discussion Starter #8
I've spoken to a couple dealers on this, and it's hard to get a straight answer. At this point, I'm mostly concerned with #3 - the periodic audible hissing noise coming from the passenger side firewall area any time the HVAC is active in any mode. For lack of a better description, it sounds like a pressure relief valve momentarily releasing pressure. The hiss lasts for about 3 or 4 seconds, then repeats approximately every minute (but it's not the same cycle duration all the time). The two dealers I've spoken to about this weren't able to say what it was and weren't able to say if other Frontiers did this, but they were guessing that it is a normal sound. I haven't requested a warranty service on this just yet - only talked to a couple service advisers.

Could anyone else confirm that you either do or don't hear this hissing noise? If it's normal, I'll drop it. If not, I'd like to get it taken care of as it is slightly irritating (admittedly, I may be overly sensitive to sounds compared to most owners).
 

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The ac compressor is supposed to come on with some vehicles. There's oil in the the refrigerant and it lubes the compressor and system to prevent seizing while it's not in use during the winter. Learned this when i was in tech school to learn how to work on medium to large diesel engines and trucks.
 

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Discussion Starter #10
Thought I'd post an update here because I've figured something out. Maybe this will help others.

So essentially, my AC has been on anytime my HVAC has been on in any mode over the first 2,000 miles of my truck's life. I went back and read the manual carefully - and it says to push the mode button first then turn the fan to the desired speed. All this time, I had been turning the fan on to the desired speed then pushing the mode button. I guess this was never enough to make the truck think it needed to shut off the AC? The first time I used the "mode button first, fan speed second" method, the AC miraculously shut off. I'm still getting the hissing noise when the AC is running when I'm in defrost mode, but at least now I can run the heater in floor only mode without the AC (condenser, evap?) constantly yelling at me.
 

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VERY INTERESTING! Mode 1st + fan speed 2nd = FTW.
 

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Thought I'd post an update here because I've figured something out. Maybe this will help others.

So essentially, my AC has been on anytime my HVAC has been on in any mode over the first 2,000 miles of my truck's life. I went back and read the manual carefully - and it says to push the mode button first then turn the fan to the desired speed. All this time, I had been turning the fan on to the desired speed then pushing the mode button. I guess this was never enough to make the truck think it needed to shut off the AC? The first time I used the "mode button first, fan speed second" method, the AC miraculously shut off. I'm still getting the hissing noise when the AC is running when I'm in defrost mode, but at least now I can run the heater in floor only mode without the AC (condenser, evap?) constantly yelling at me.
This kind of info could help out quite a few folks who are potentially & unknowingly running their AC compressor w/o their knowledge. Can see this restoring a bit of fuel economy as well.
 

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My HVAC gives me a hissing when it is running in any form as well. Heater, AC, any of it. Happens when accelerating at various speeds, going up an incline, etc. 2019 Nissan Frontier. It feels like a normal operation but I have been wondering if something could be wrong...

What is your conclusion?


Sent from my iPhone using Tapatalk
 

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Discussion Starter #14 (Edited)
My HVAC gives me a hissing when it is running in any form as well. Heater, AC, any of it. Happens when accelerating at various speeds, going up an incline, etc. 2019 Nissan Frontier. It feels like a normal operation but I have been wondering if something could be wrong...

What is your conclusion?


Sent from my iPhone using Tapatalk
Ever since I changed my order of operations (mode button first, then fan speed), I no longer get the hissing in floor only heater mode. It will still intermittently hiss whenever the AC is on (which comes on automatically in defrost/defog mode).

I don't have a solid conclusion as to whether or not this is normal. I am less bothered by it now that I can run the heater without hearing it all the time. I have not been back to the dealer about this issue since my last posts - they irritated me over other issues they claim were normal, so I needed to take a break before starting up the warranty battle again.

I think what I'm going to do is wait until this summer and see how the AC performs. It will be a lot easier to go in for warranty service if I can just say the AC is not working properly. If, however, the AC does work properly this summer even while making the noise, well, I'm not sure if I'll continue to fight it. I may give it one more shot at a dealer and drop it off this summer to have the sound fixed or officially claimed to be normal. I do realize that I am more sensitive to sounds than the normal Joe, but this does not sound normal to me.

EDIT: I realize I forgot to mention that I determined issue #1 from the first post was deemed to be 100% normal - I think I ended up reading in some official documentation that it was normal, and the loaners Nissan gave me while my truck was in the shop even did the same thing.
 
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