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Opinions on AC symptoms

wilsonny

Spa-Francorchamps
Joined
1 Dec 2012
Messages
357
I've been on a bit of a journey with my AC system. In the last two years, it's had a new compressor, condenser, evaporator, expansion valve, ccu service by tore, fresh air flap motor changed and new blowers. After that lot, up until recently it's been working well, but I still had an annoying slow leak from the small bore pipe in the sill, so wanting it perfect, I set about replacing that line (total pain in the backside), putting a new dryer on and getting it regassed... All fine, except now it won't produce any cold air, all I get is ambient temperature air even on the max button.

I've checked for leaks... Non found and checked pressure in the system which shows "full" on my gauge (36 psi I think at static). The compressor engages and the high side pipe gets hot, low side cool (not cold) and strangely the compressor runs constantly unless I switch the AC off at the ccu. So even if I set the ccu temperature at 25 degrees and it's blowing out heated air, the compressor is still engaged and running but turns off if I switch the AC off manually.

Any ideas ?

I've tested all the flaps and fans using scantool and they all appear to work perfectly and no fault codes raised.

Despite having changed it being only two years old, I'm thinking a failed expansion valve is the most likely cause ? Could be I dislodged some dirt into it when changing the line ? Or could be a blockage maybe ?


Any suggestions welcome, bit stumped with it at the moment.
 
I can't comment on A/C pressures, but it looks like you have a pressure/cooling system problem, and not an electrical problem.

If the compressor does not cycle at about 20°C ambient, the evaporator does not get cold enough. The only regulating element for the compressor clutch is the evaporator temperature sensor. In normal A/C operation, the compressor (clutch) is activated until the evaporator is cooled down to 4°C. The compressor is then disabled until the evap is warmed up, then the clutch engages again. This is the normal cycling of the A/C compressor clutch, and in a 20°C environment, this happens with 20-30 seconds intervals.

I hope this helps narrowing down this problem.
Cheers,
Tore
 
I can't comment on A/C pressures, but it looks like you have a pressure/cooling system problem, and not an electrical problem.

If the compressor does not cycle at about 20°C ambient, the evaporator does not get cold enough. The only regulating element for the compressor clutch is the evaporator temperature sensor. In normal A/C operation, the compressor (clutch) is activated until the evaporator is cooled down to 4°C. The compressor is then disabled until the evap is warmed up, then the clutch engages again. This is the normal cycling of the A/C compressor clutch, and in a 20°C environment, this happens with 20-30 seconds intervals.

I hope this helps narrowing down this problem.
Cheers,
Tore
Thanks Tore, that's really helpful to have your expertise to confirm electrical side appears to be ok.

Would you agree with my analysis that the most likely failure is the expansion valve from the symptoms ? With the compressor high line hot, and the return line at ambient temperature, that indicates to me that the compressor is working well in compressing the refrigerant into a gas and that the flow of refrigerant is passing through the condenser where it is being cooled to ambient before returning. To me this suggests that there is no blockage and that the only failure is that the expansion valve is not operating to perform the phase transition into the evaporator and generate cold air to the cabin. This would also align with your explanation of the trigger for switching the compressor off being the evaporator temperature sensor reaching 4 degrees.... If the expansion valve is not working, the evaporator is not getting cold and hence the compressor never gets switched off.
 
Last edited:
I am sorry, cooling systems is not my field of interest or insight.
Cheers,
Tore
 
+1 for expansion valve or evap temp sensor if you have pressure and compressor is running
 
+1 for expansion valve or evap temp sensor if you have pressure and compressor is running
Thanks, I'm thinking if it was the temperature sensor faulty, id see it switching off the compressor. So with it not producing any cold air it does seem to be the expansion valve most likely.
 
The compressor running continuously would indicate to me that temperature demand from the CCU is never being met, however the fact it still runs when 25 deg is selected is puzzling. Suggests an issue with temperature sensors perhaps, any faults come up with a T-OBD/Durametric?

Alternatively….

Are you 100% sure the system was regassed after the new pipes were fitted, if they only did a pressure test you may be pumping Nitrogen rather than refrigerant around the system which may result in what you’re experiencing. Unlikely but possible…
 
The compressor running continuously would indicate to me that temperature demand from the CCU is never being met, however the fact it still runs when 25 deg is selected is puzzling. Suggests an issue with temperature sensors perhaps, any faults come up with a T-OBD/Durametric?

Alternatively….

Are you 100% sure the system was regassed after the new pipes were fitted, if they only did a pressure test you may be pumping Nitrogen rather than refrigerant around the system which may result in what you’re experiencing. Unlikely but possible…
Thanks... I'm coming to the same conclusion regarding the regass not maybe being done right... I've now got hold of a better set of manifold gauges and the non active pressure (car not running for 24hrs) is at 27psi which I understand indicates the system is below required fill pressure. Also when retesting now a few days later, the compressor won't now engage, so I suspect it's been inhibited because of this low pressure. Time to try a regass I think before anything else. I'll feed back on the outcomes.

One thing I have found useful is a leak tester... Fantastic device, really cheap from Amazon and detects little wiffs of gas from my valves (which I'm going to replace) but no leaks elsewhere.
 
Update on this... So after changing the Schrader valves just in case and finding a new garage that gave me some confidence they would do a proper regass... It's all working fine, blowing nice and cold 7 degrees. So thanks for input on this and avoiding me jumping to looking for problems. I should have really known, it took more than an hour today to do a vacuum and refill whereas the last garage seemed to be able to do it in twenty minutes... Clearly they didn't do it right.
 

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