A/C Woes and questions

[mykg4orce]

Hello!

My car is about a year old while under my care. The A/C has worked very well from the day I bought it. Just last couple of days the A/C started to make a hissing sound but was still functioning. Then yesterday I could still hear the hissing sounds fade in and out very gently but there was no cold air from the vents. I stopped at a local parts store and bought a freon pressure gauge, I connected it to the Low port and the gauge read about 80 psi?

Any ideas?










C230 Komp
2000
160K

[jnenad16]

80psi with the ac on or off?

nenad

[mykg4orce]

with engine off

[jnenad16]

if your system pressure is 80psi with the system off, then the system is charged.
where does the hissing come from?

nenad

[mykg4orce]

when I turn the knob to the number 1 position or 2,3,4,5 whichever I hear a very gentle cycling of hissing. Fading in and out.

I checked the fuses, and found none to be replaced. I also hooked up the scanner and found read no codes.

[jnenad16]

it might be that the duo valve is releasing coolant through the heater, so the hot air from the heater is mixing with cold air from the evaporator, and the air coming out of the vents is warm.

nenad

[mykg4orce]

But for that to be possible the air would have to be hot or at least warm. The air from the vents isn't either, it feels like the air outside or slightly warmer than it.

hmmmm what to do

[jnenad16]

the air coming out of the vents wont be hot, it would be mildly warm at most. you should check your compressor if its running or not when this happens.

nenad

[mykg4orce]

Okay i checked the compressor and its not turning at all..... So i guess thats why the A/C wont work...but why ....

[Lensolo]

Originally posted by mykg4orce
Okay i checked the compressor and its not turning at all..... So i guess thats why the A/C wont work...but why ....
The compressor turns itself off when it's below a certain pressure. Sounds like a leak somewhere. Might be a dealer issue.

[mykg4orce]

anyway of finding out what this pressure value is?

[strictlyspeakin]

I don't know what the gauge would read at the low and high sides, check points. But I did find this

<2 bar or >28 bar at the receiver drier pressure sensor will disengage the compressor.

That's about <29psi or >400psi


In looking for this answer I stumbled across all sorts of sensor that might shut the compressor off. Coolant temp, refrigerant temp. I don't know

Isn't the gentle hiss normal during A/C operation? I always seem to remember it being normal.

[mykg4orce]

should I attempt to recharge the system myself?

the gauge I bought can also be used to refill the gas....

[strictlyspeakin]

Out of my realm of experience. Nenad said he thought your charge was good.

[mykg4orce]

well now that I think about it, the instructions on the charge kit read that in order charge the system the A/C needs to be on (so that it can suck the gas into the system?), therefore I wont be able to charge the system without the compressor engaging.....

hmmmm quite a puzzle this is indeed.....

[jnenad16]

this is the basic way ac works:
assuming that all electrical requirements are met, the system pressure needs to be around 50psi at rest for the compressor clutch to engage. once the compressor is on, the pressure will either double or triple(depending on the volume of the system) and this becomes the working pressure. now, normal working pressure is usually between 150psi and 200psi at idle, and should stay under 300psi under load(can be higher, but system efficiency and stability will suffer).
when charging an empty ac system with the compressor off, you will always be able to charge up 100psi or more of pressure, unless there is an obstruction in the system(dirty or plugged) which will prevent the freon from spreading throughout the system. this is the reason why you need to change the filter/dryer every time you perform repairs on the ac.

nenad

[mykg4orce]

your help is very much appreciated...your advice will hopefully lead me into the right direction.

thank you

[mykg4orce]

ok well I bought a can of duracool or something and when I hooked up the gauge I noticed that now my pressure form the low side with engine off was nil. So between 3 or 4 days I lost all the pressure. I think its safe to assume there is a mjor leak somewhere.

As I added the can of refrigerant the compressor kicked in and the A/C was blowing semi-cold air. I will check tomorrow morning to see if its still holding charge if not then I guess im about to replace the condenser? sigh...

[jnenad16]

you should check where is the leak coming from before you start wasting money on parts that are probably good. have a shop do a UV dye test.

nenad

[mykg4orce]

understood