Another AC question

[mlipmd]

Somewhere 1 to 1/2-2 years ago my AC was leaking and i found it to be from the high pressure Schrader valve (a common problem). I evacuated the system and recharged it when I replaced the valve and it has worked great since then. Today I went to use the car and the system only blows warm air (it was 85-88 degrees here), and when the system was first turned on the green light flashed for about 15 sec, then stopped. When I came home and restarted the car 10 min later the same thing happened. When I interrogate the system I get the 09 code which I knew would happen. I then hooked up a can of Freon to the low port with the car running and AC on, and got a really high pressure, way into the red scale on the dial. After a few moments of the car running, the compressor came on and because the pressure was so high no Freon could be added to the system. With the compressor on, the low side pressure was still really high, in the red scale. I don't know why the pressure should all of a sudden be high, so just for the helluvit I let some gas out to get it down into the green zone on the scale. Still no cold air out of the vents and I am unable to add more Freon into the system. All of this time the compressor runs and no strange noises come from anywhere. The pipes are all the same temp, no temp difference between high and low. I also disconnected the battery for a few min. to wipe out the 09 code but the compressor ran with the code on anyway and when I interrogated the system the second time, even with the green light not flashing, the 09 code came back. And although I had gotten the pressure into the green on the scale, when I restarted the car it was in the red again.
So do I have a blockage in the system somewhere and where do I go to find it?
Thanks.

[secondchance]

Perhaps, a professional shop with AC equipment vacuuming the system might dislodge whatever may be creating the blockage?
Just a thought...
BTW - did you check and see if secondary cooling fan (on the driver side) was running when the AC was turned on?

[mlipmd]

Doing some further research, the problem may be from either a failed compressor or a stuck open expansion valve, and you can tell by a set of gauges which I have to get. I'll keep you posted.

[mackguy]

My understanding is that when you get the code, it should not be trying to run the compressor, and if the compressor's not running, I think the pressures won't mean much.

If you're sure the compressor's running when you have the code, then it would seem to indicate other problems in the system...

If you find the compressor actually isn't running, you'll need to get it running to add refrigerant. The FSM mentions bypassing the safety system in order to get the compressor to run for this step, or you can try disconnecting the battery for a bit to reset the system

[mlipmd]

If you read my post, I said that the compressor runs and cycles on and off, and that green light only flashes for a few times and then stops. The 09 code has to be reflecting some other kind of system error because the system is not low on Freon. Another possibility is a bad low pressure sensor.

[mackguy]

Yes, I did read that, which is why I responded as I did.

The light should only flash for 1min, so that behavior is normal.

But per the FSM the compressor shouldn?t be cycling on at all if a code is set, so that seems like something faulty in the control circuit perhaps, if it?s cycling.

In case you don?t have access to FSM, here?s the info, and diagnostic procedure for DTC09.

Originally Posted by mlipmd

If you read my post, I said that the compressor runs and cycles on and off, and that green light only flashes for a few times and then stops. The 09 code has to be reflecting some other kind of system error because the system is not low on Freon. Another possibility is a bad low pressure sensor.
But a high low pressure reading would point to an open expansion valve.

[mlipmd]

I read all that but I don't understand why the low side has such high pressure. My thought now is that the compressor is at fault and not sucking down the refrigerant after leaving the evaporator and the system just has equalized pressures on both sides. One of these days in the near future I am taking it to an AC guru who is familiar with these cars so he can diagnose the problem and maybe I'll let him repair it. If I need to replace the compressor, also the accumulator and orifice tube should be replaced at that time.

[mackguy]

They do strange things sometimes.
Last year I was prepping our 2005 Bentley for a family trip, and the A/C had been a little underwhelming, so I got one of the typical auto parts store cans and topped it off.. Lowered the temp coming out of the vents almost 10 degrees. Success!
Then, when we left home, it just kept getting hotter in the car. We had an overnight stay planned, so my wife was calling every shop in the area to see if we could get the AC checked. Many couldn't do it on short notice, some didn't want to mess with a Bentley.
A Nissan dealer was the only positive response. I was worried the compressor had failed or something, but they did a standard recharge on the system and all was well. They said it was just way over-filled.

Moral of that story is that I don't really trust the little store cans since it said it was "green" and was working well, but then went way high. Basically as you're describing.

[mlipmd]

You guys don't understand or didn't read the original post. My AC has been working fine for years and quit all of a sudden, I didn't recently refill it relying on the can gauge which maybe was inaccurate. My low pressure is high, OK? The system is not and has not ever been overfilled. The question is it is why it is high and I think it may be a symptom of a failed compressor, with the reasoning I outlined above. I will find out next week.

[mackguy]

Originally Posted by mlipmd

You guys don't understand or didn't read the original post. My AC has been working fine for years and quit all of a sudden, I didn't recently refill it relying on the can gauge which maybe was inaccurate. My low pressure is high, OK? The system is not and has not ever been overfilled. The question is it is why it is high and I think it may be a symptom of a failed compressor, with the reasoning I outlined above. I will find out next week.

I read your original post just fine, but I will admit I don't understand why you say the compressor is running when a DTC code is present, since that shouldn't be happening, which as I mentioned indicates some other fault in the system.

My suggestion was to get the car properly evacuated and refilled, based on my similar experience of having it working great, then some time later it was suddenly over-pressure, which sounds like the exact fault you have. In my case that was resolved by getting it recharged at a dealer.

Maybe I have misunderstood the symptom "My AC has been working fine for years and quit all of a sudden", which sounds identical to mine, except that mine quit working a few days later, while yours worked a bit longer. I am equally puzzled as to how it ended up over-pressure after working perfectly for some time.

In any event, it seems you need the help of an AC professional at this point, do let us know what they find, I'm really curious as to what can cause this!