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Something strange happening with my AC

abbouddi on Fri May 09, 2008 1:22 AM User is offline

Year: 2003
Make: Peugeot
Model: 307
Engine Size: 1600
Refrigerant Type: 134
Ambient Temp: 30

Hi, I have something strange happening with my Peugeot 307 AC
I have a small leak almost in the evaporator, and charge is staying about 2 monthes. Recently I went to a technician to recharge, He vacuumed the system, then charge oil, then charge freon to 35 PSI. When he finished AC is blowing cold air, but compressor didn't cut off and restart (as it was before), and now whats strange happening is when fan speed is highest, air is very cold, but at lower speed fan air is becoming less cold, and when I stopped driving (the car is idle) air is very cold even at low fan speed; so my problems are:
1- when I am driving and fan at low speed, air is not as cold as I used to
2- Why compressor is not stopping and engagging

I guess this problem is from extra pressure of freon, is this right before I remove some charge?

Chick on Fri May 09, 2008 7:21 AM User is offlineView users profile

Don't remove any charge, you'll screw the system up! Only run the car with the full charge in it. Use a vent thermometer to check the air temp coming out, and then go back to your tech with that information. On lower speeds the compressor may be shutting down due to evaporator temp, and the air may warm up a little while the compressor is may be normal..

Email: Chick


Freedoms just another word for nothing left to lose

Karl Hofmann on Fri May 09, 2008 10:23 AM User is offlineView users profile

Why has it been charged to 35psi?? The Pug 307 uses a Sanden SD6V12 Variable displacement compressor... These cars need to be charged by weight only... And whilst you are at it... Fix the leak

PS Variable displacement compressors do not cycle on and off.. and running them short of refrigerant will kill them. Take it to someone who knows what he is doing

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

Edited: Fri May 09, 2008 at 10:28 AM by Karl Hofmann

abbouddi on Sat May 10, 2008 1:35 PM User is offline

Thanks for ur replies. On lower speed fan, compressor is not shutting down, while air is less cold. For example when i was driving at night with low speed air, air become less cold in 15 min, although compressor is still working, so i put fan to highest speed for 1 min. then returned to lower and cold air will be blown. If i am idle i will not get this issue.
Then does removing charge will harm my system?
And Mr Hofmann, may u explain more about variable displacement compressor?
thank u all

Karl Hofmann on Sat May 10, 2008 8:34 PM User is offlineView users profile

Conventional ac compressors either run at 100% or do not run at all, this is what you see when the clutch cycles on and off.... This cycling is controlled by the temperature sensor which measures the air temperature coming off the evaporator and will shut off the compressor when the air off temperature gets close to freezing point.... This prevents the evaporator from freezing up

Variable displacement compressors do not rely on the evaporator temp sensor and controls their output by varying the displacement of the compressor.. It has a mechanism that can vary the piston movement and so can pump more or less refrigerant, this it does by monitoring the suction pressure... low suction pressure means that the evaporator is cold and so will reduce the displacement of the pistons so that less refrigerant is compressed, the evaporator becomes less cold and so does not freeze. The nice thing about this system is that when used in our temperate climate, the compressor can be left running and they will only compress the refrigerant that it needs to and so uses less energy in when the weather is cooler... thus saving a little bit of fuel

Earlier variable compressors still utilise magnetic clutches to turn the compressor on and off and also controls displacement via a displacement control valve.... Later compressors run even when off, have no magnetic clutch and the displacement valve has been replaced by an electric solenoid valve which is controled by the HVAC control module.. these were first seen (I believe) on the Skoda Fabia but are very common indeed now

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

abbouddi on Tue May 13, 2008 7:14 AM User is offline

Thanks Mr Hofmann, but I still have some questions: How can we charge by weight? All technicians here in Saudi Arabia have Freon cans with gauges ie they can only check for pressure, and what is the average pressure to be present in any AC : is it between 30 and 35 psi as everybody is stating?
I found finally what happen exactly, it is when I press on the accelerator the compressor will shut down for few seconds then work again. thats why air is less cold, but when idling compressor is always working; that's why air is colder. Is this freezing point of evaporator when I am accelerating?

Finally do you recommend to use any chemical for stop leak like Stop Leak Pro from Cliplight?

mk378 on Tue May 13, 2008 10:13 AM User is offline

Charge by the net weight filled in the cans. You can do partial cans by weighing them on a scale when full and then after some has been charged. Charging by weight can only be done by starting with the system empty. Start with a vacuum in the system and charge the car maker's specified total weight.

The problem you have now is likely one of excessive high side pressure. Surely someone over there has a standard manifold with two gauges to confirm that. Measuring only the low side pressure with a single gauge is particularly useless on a variable compressor system. It will always be about 20-30 psi over a wide range of conditions, both normal and abnormal.

Excessive high side pressure is caused by 3 things primarily:
* Poor cooling of the condenser (defective fans or restricted airflow)
* Air in the system (failure to use a vacuum pump before charging)
* Overcharged with refrigerant

Under no circumstances should any type of "stop leak" product be used. There's a 99% chance it will do more harm than good. The only cure for leaks is to find the leak and replace the leaky part.

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