A/C fan speeds up from time to time

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486
1.8 16v
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Joined: Thu May 10, 2018 9:49 am

A/C fan speeds up from time to time

Post by 486 »

Latterly my A/C fan speeds up for 1-2 min and restores to normal level. Everything with A/C was OK until this spring. One time the fan stopped for 10-15 seconds, then run with normal speed. After about a month it happened again. It has not stopped for 1-2 months but since recently several times per week happens the speed-up problem. Is it possible that the reason for this behaviour is the temperature sensor (with small fan) near the lamp? If it gives unstable and unreal temperatures, the fans will speed up and restore. For example 24-25-24°C, then 35-36°C, then again 24-25°C. Can I read the values of interior temperature from OBD?
Last edited by 486 on Thu Aug 13, 2020 9:11 am, edited 1 time in total.
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Doggy
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Re: A/C fan speeds up from time to time

Post by Doggy »

The interior temperature sensor gets blocked up with dust etc. worth cleaning it out
viewtopic.php?p=83025#p83025
2002 HDi 2.2 Exec Estate, (2008-12) (wonderful)
2003 HDi 2.2 6-speed Exec Estate (2012-19) (also a gem)
2009 Citroen C5 2.0 HDi VTR+ Estate (godawful heap)
2008 BMW E91 330i touring (we shall see......)
486
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Re: A/C fan speeds up from time to time

Post by 486 »

It seems the problem is in (1) or (2) in the following scheme. But I cannot understand how to access the sensors - is it necessary to remove A/C control panel (above CD audio) or they are accessible in other way?
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Temperature probes
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486
1.8 16v
Posts: 88
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Re: A/C fan speeds up from time to time

Post by 486 »

My old problem started again. I am nearly sure that sensor 1 (evaporator) is the reason. Last year I replaced it and this solved the problem. What can be the reason such part to stop working again?
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Doggy
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Re: A/C fan speeds up from time to time

Post by Doggy »

I think it's unlikely to be the sensor twice. More likely corroded connections under the carpets in the drivers footwell, or something similar.

Do you still have the old sensor?, (worth comparing them).

As it's a 2-wire temperature sensor,it will very likely be a thermistor of some sort. Try measuring the resisitance between the pins. No idea what it should be, but probably something between100 to 10000 ohms. It should not be zero resistance or open circuit.

It's intended to measure temperatures between roughly -10 and +40 degrees, so should have a noticeable change in resistance if you were to put it in your freezer for a time, then measure as it warms to room temperature
2002 HDi 2.2 Exec Estate, (2008-12) (wonderful)
2003 HDi 2.2 6-speed Exec Estate (2012-19) (also a gem)
2009 Citroen C5 2.0 HDi VTR+ Estate (godawful heap)
2008 BMW E91 330i touring (we shall see......)
486
1.8 16v
Posts: 88
Joined: Thu May 10, 2018 9:49 am

Re: A/C fan speeds up from time to time

Post by 486 »

First time, 5 years ago, it failed after several ignition attempts (frozen fuel). Next time (2020) I think it was similar - low battery before alternator refurbishing. But this year I don't remember low battery / eco mode warning. It sounds like impossible connection between low voltage and temperature sensor failure but my experience says it is possible. Or the connector is bad. Unfortunately local dealer diagnostics are not good. Last time they told me that my problem is with intenal air probe (#5 on above scheme, near the lamp). I had 2 additional sensors and tried without success.
486
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Re: A/C fan speeds up from time to time

Post by 486 »

PS: Is there method to deactivate automation of A/C? AFAIK, when temperature is 30°C, it is always heating (100% heat/0% cold). I want temporarily to deactivate A/C while searching for sensor replacement and avoid frequent position changes of valves.
486
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Re: A/C fan speeds up from time to time

Post by 486 »

I found another sensor (OEM code 6445.S4). ServiceBox says it exists on my 406 but cannot access the scheme with location.
frog
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Re: A/C fan speeds up from time to time

Post by frog »

Here it is:
6445 S4.png
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Current "fleet":
2003 406 Estate 2.0HDi 110 - 7 seater - just hit 650.000 kms :cheesy:
2001 Citroen Saxo 1.6i 8v 100

Previously owned:
2000 406 Sedan 2.0 HDi 90
2000 406 Coupé 2.0i 16v 138 - Riviera Blue

PP2000 user, can help with faults / diagnostics in the Netherlands.
486
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Re: A/C fan speeds up from time to time

Post by 486 »

Thanks. It seems "Search" button in ServiceBox finds all options for a detail. I supposed that it filters only for my VIN.
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