Heater/AC query

Hi, I'm in the UK. The outside temp is 17C and I've got the cabin temp set to 16C. By my reckoning, the air flowing into the cabin should be at 17C with the AC switched off. It starts off that way but the air vents start blowing warm air once the engine has warmed up so I then have switch on the AC. Does anyone else notice this? Is it a fault? If so, what's the likely cause?
 
Our Micra has the manual HVAC controls rather than the automatic, but I would assume 16c was the lowest setting?

With my former Qashqai and Pulsar, and now Megane with 'digital' HVAC controls, as long as its not set to auto, 16 would be 'uncooled' air, but with auto enabled, it will slightly open the blend door to mix in some hot air until the cabin was at the set temperature, the fans will lower and it will try and maintain that set point by adjusting the blend door and fan speed.

Auto mode relies upon a temperature sensor to detect the cabin temperature to make adjustments. Sometimes they are not in an in an ideal position or maybe not calibrated exactly and either read too hot or too cool. 17c outside air temp is probably borderline

If you dont have auto switched on, It could also be that the blend door is not closing, either partially for fully.

Are you able to describe your symptom in a little more detail?
Are you running the HVAC with auto mode on or off?
If auto mode, what was your HVAC doing a couple of weeks ago when the outside air temp was in the 20's?
When you say warm air, is it luke warm, or does it eventually get hot if left long enough?
What happens if you increase the set point, does it pushed out hotter air?
 
Many thanks for your very helpful reply. My observations have been made while running it in Auto mode and, yes, 16C is the lowest temp setting available. When the outside temperature is warmer, over 20C say, the cooling is again initially effective until the engine warms up when it becomes less so.
I'll do a few more experiments as you suggest, and will report back.
Incidentally, the a/c system has recently been serviced and recharged so I don't think there's a problem with that.
Thanks again.
 
Our AC hasn't worked for years! But we did recently have a problem with the heater control knob - a clip holding a cable in place came loose which meant the outer sheath would move rather than the inner control cable. The result of that was it would not actuate the blend door enough to full hot position.

I am not sure if the manual and automatic HVAC unit behind the dash is the same, but on the manual at least, you can see the leaver which controls the blend door (or mixer door) from the passenger footwell, its just in front of the pollen filter cover - you just need to contort yourself into a funny position. I could not get the cable clip off, nor could I get it to re-grip by itself, however with the use of a small enough zip tie I was able to apply enough clamping pressure to hold the cable in situ!

I would see what happens with auto off, AC off and set to 16, allow engine to warm up fully then make an observation. I know the DIG-S can take some time to warm up fully so make sure its had a good run before observing and testing. Once warm and you have observed 16c, crank it right up and see what happens. Also listen out for any noises.


Some notes from the workshop manual....

A/C UNIT ASSEMBLY : Air Mix Door Motor INFOID:0000000006441684
• Air mix door motor consists of motor that drives door, PBR (Potentio Balance Register) that detects door
position and LCU (Local Control Unit) that performs multiplex communication control (LIN) with A/C auto
amp. Refer to HAC-18, "Door Control".
• Rotation of motor is transmitted to air mix door by lever. Air flow temperature is switched
 
Found the diagram of the auto unit and its not the same. It looks like the motor that controls the blend dooor is on the drivers side, marked as 13 in image A below.

1628448513526.png

1628448538923.png
 
Hi, I'm in the UK. The outside temp is 17C and I've got the cabin temp set to 16C. By my reckoning, the air flowing into the cabin should be at 17C with the AC switched off. It starts off that way but the air vents start blowing warm air once the engine has warmed up so I then have switch on the AC. Does anyone else notice this? Is it a fault? If so, what's the likely cause?
A technician has since looked at this problem and discovered that one of the motorised flaps wasn't closing fully. He lubricated it and it now works as it should.
 
Our AC hasn't worked for years! But we did recently have a problem with the heater control knob - a clip holding a cable in place came loose which meant the outer sheath would move rather than the inner control cable. The result of that was it would not actuate the blend door enough to full hot position.

I am not sure if the manual and automatic HVAC unit behind the dash is the same, but on the manual at least, you can see the leaver which controls the blend door (or mixer door) from the passenger footwell, its just in front of the pollen filter cover - you just need to contort yourself into a funny position. I could not get the cable clip off, nor could I get it to re-grip by itself, however with the use of a small enough zip tie I was able to apply enough clamping pressure to hold the cable in situ!

I would see what happens with auto off, AC off and set to 16, allow engine to warm up fully then make an observation. I know the DIG-S can take some time to warm up fully so make sure its had a good run before observing and testing. Once warm and you have observed 16c, crank it right up and see what happens. Also listen out for any noises.


Some notes from the workshop manual....

A/C UNIT ASSEMBLY : Air Mix Door Motor INFOID:0000000006441684
• Air mix door motor consists of motor that drives door, PBR (Potentio Balance Register) that detects door
position and LCU (Local Control Unit) that performs multiplex communication control (LIN) with A/C auto
amp. Refer to HAC-18, "Door Control".
• Rotation of motor is transmitted to air mix door by lever. Air flow temperature is switched
A technician has since looked at this problem and discovered that one of the motorised flaps wasn't closing fully. He lubricated it and it now works as it should.
 
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