C5 2001 - aircon not cooling drivers side

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aspire_helen
Posts: 36
Joined: 08 Sep 2020, 22:12
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C5 2001 - aircon not cooling drivers side

Post by aspire_helen »

First use of the aircon this summer, and I found the aircon has stopped cooling the driver’s side air (right side). The passenger side seems OK, but may not be as cool as before – not sure. The driver’s side will only blow ambient to hot air. The immediate thought is – faulty driver side temperature mixer/blender motor or flap broken/stuck/restricted etc. A common problem on C5 Mk2 s and Peugeot 407s. But that turned out NOT to be the problem........I removed the motor and checked both the motor and flap for full and free movement - all worked perfectly.

After a lot more investigation than proved necessary (doh!), I finally removed the temperature probe, low on the driver’s side, and ran my own digital temperature probe across the output face of the evaporator matrix, and found that the passenger side was 6degsC whereas the driver’s side was 19degsC ie ambient. Note – the aircon was set to 16degs both sides, with max fan, engine idling.

Before I delve deeper into other possible causes, has anyone experienced similar, and is this indicative of typical aircon circuit fault?? Eg re-gas needed or more serious? I have read that.....“BMW HVAC systems, by design, will preferentially cool the driver's side when the total system cooling capacity is compromised by low refrigerant. “ I wonder if Citroen is the same. As Citroen's heater unit is designed for left hand drive, the passenger side on UK models would be prioritised, as in my problem.

By the way, I gained access to the drivers side mixer/blender motor by cutting away a small piece of the dashboard under the steering wheel and removing a plastic tubular conduit in the dashboard. See photos. The pollen filter and inlet face of the evaporator matrix are clean and dry.
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ozvtr
Posts: 205
Joined: 13 Oct 2020, 01:11
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Re: C5 2001 - aircon not cooling drivers side

Post by ozvtr »

aspire_helen wrote:
10 Jun 2022, 21:38
is this indicative of typical aircon circuit fault?? Eg re-gas needed
Yes. If there is not enough refrigerant, only the part of the evaporator closest to the outlet of the thermal expansion (TX) valve will get cold.
The evaporator has a (refrigerant) "in" side and an "out" side. The 'in' side is closest to the outlet of the TX valve. So the evaporator will get cold on the 'in' side, absorb the heat of the air passing through it and then be at ambient temp on the 'out' side. Normally the entire evaporator and the vapor line (going back to the compressor) will be cold. If that 'in' side is split out to one side of the car, well, that side gets the cold(ish) air.
Typically the TX valve will tend to hiss louder as the refrigerant level gets lower and the valve is now passing just gas instead of converting liquid into gas.
aspire_helen
Posts: 36
Joined: 08 Sep 2020, 22:12
x 9

Re: C5 2001 - aircon not cooling drivers side

Post by aspire_helen »

ozvtr
Thanks for your quick response. I have booked in the car for a leak test and full recharge.
It is interesting that the system measures the vent outlet temperatures of the left (passenger) dash and feet, but measures the evaporator output on the right (drivers) side. Normally, the evaporator output would be the same across the matrix face, but I wonder if there is a design reason why the right side is measured, not left.
Currently, the evaporator output sensor will be returning ambient temperature. I wonder if that would cause the compressor to go into "over-drive" trying in vain to reduce the temperature !!
ozvtr
Posts: 205
Joined: 13 Oct 2020, 01:11
x 58

Re: C5 2001 - aircon not cooling drivers side

Post by ozvtr »

aspire_helen wrote:
11 Jun 2022, 20:34
It is interesting that the system measures the vent outlet temperatures of the left (passenger) dash and feet, but measures the evaporator output on the right (drivers) side. Normally, the evaporator output would be the same across the matrix face, but I wonder if there is a design reason why the right side is measured, not left.
The sensor closest to the evaporator is really only looking for a "freezing" condition. So that the evaporator doesn't ice up and block the air flow. The second sensor allows the climate control unit to measure the rise in temperature from one point in the duct work to the cabin and "anticipate" how much cooling is required to get the cabin to the required temperature. This reduces over and under shoot of the temperature. My guess is the sensor is before the air is split out to the passenger side but it's on the passenger side?
aspire_helen wrote:
11 Jun 2022, 20:34
Currently, the evaporator output sensor will be returning ambient temperature. I wonder if that would cause the compressor to go into "over-drive" trying in vain to reduce the temperature !!
There must be just enough refrigerant/pressure in the 'high' side of the system for the engine ECU to allow the compressor to run. If the pressure falls below a certain point the engine ECU wont engage the compressor. There are variable displacement compressors that are electrically controlled to compress more or less refrigerant. This produces a more controlled and efficient way to cool the evaporator and therefor the cabin. I do not know if your car has one or not. If so, yes the climate control ECU will be requesting maximum displacement to try and make the evaporator colder. If not, the engine ECU will be requested to run the compressor for longer (or continuously).
The climate control ECU, the BSI and the engine ECU all have their part to play in the air conditioning/climate control system. But the engine ECU has the power of 'veto' to engage or disengage the compressor clutch!
aspire_helen
Posts: 36
Joined: 08 Sep 2020, 22:12
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Re: C5 2001 - aircon not cooling drivers side - and rusted service ports

Post by aspire_helen »

Thanks for all the info. It is always nice to hear from experts in such technical detail. Unfortunately, my first problem is that the service ports are badly rusted . The caps do not protect the external surfaces of the ports....and who thought it a good idea to position them adjacent to the compressor, facing down (with caps able to collect water!) and only accessible from underneath with the under-body panel removed!? Moreover, the expanding rust had split one of the caps. Fortunately, the cap seals have successfully protected the internal M8x1 thread and valve which look fine. I have de-rusted and smoothed the external mating surfaces in the hope that the quick release couplings will still attach and seal when I take it the aircon garage this week.

A note of advice - check the condition of your ports, and add extra anti-corrosion protection to the external surfaces where the quick release couplings attach.
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ozvtr
Posts: 205
Joined: 13 Oct 2020, 01:11
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Re: C5 2001 - aircon not cooling drivers side

Post by ozvtr »

That's strange. The fixed lines are typically aluminium, but those lines are 'rusting' (oxide of iron). Are they steel lines ( I wouldn't think so)? Where is the iron oxide (rust) coming from?
I'm glad I don't have to deal with salting of the roads over here.