I used one of those "R134a" suicide can recharge kits a few weeks ago because my A/C was making a strange whirring sound at around 2500 rpms on hot days that did not happen with the A/C off.


Well, doing so did not fix the noise, but the cheap gauge on the A/C kit did indicate that the low side pressure was at around 35 psi, and did not budge when I added more refrigerant. I added a whole 16 ounce can of R134a and because of this, I was almost certain that I had overcharged it. However, A/C performance improved dramatically after doing this.

So today I decided that I was going to take another look at it. I bought some cheap AC manifold gauges, and hooked them up to the high side and low side.

Ambient temperature was about 80-85 degrees. After turning on the A/C, the low side was reading only 30 psi and the high side was reading about 200-210. Revving the engine would cause the psi to drop on the low side.

I believe that these readings would indicate that the system is undercharged, no?

But in disconnecting the gauges, I must've gotten confused, because suddenly refrigerant started spraying out of the center hose (and into the atmosphere), and now the A/C doesn't blow nearly as cold, but it blows cold enough. The strange whirring sound is still there.

I am going to try to take it to a shop this week and let them do the procedure properly. What do you guys think? I imagine there is air in the system.

BTW the compressor never cycles on and off. It seems to just stay on all the time. And before I worked on it today, the fans for the A/C under the hood seemed to come on right when I started the car up and stayed on really loud at full speed.

 

Do you guys ever notice your A/C cycling on and off?

 

No, I've never noticed it cycling on/off. That's one reason, when I'm driving in the mountains or cool weather (say below 70*F) I delibertly go the the Climate page and disable the a/c.

One of the reasons I do this is, I owned a Ford product that I KNOW never cycled on/off and there was seemingly no way to turn just the compressor off alone without turning the fan off.

Like I sayd, I don't actually know if it cycles. I never noticed it if it does by listening.

EDIT: Now there's an idea. I could turn the a/c on say to 65 degrees and let it run. Then go to the Climate page and disable it to see if I can tell by sound when it goes off (the compressor).

 

You can definitely tell the compressor turns off when you turn off the A/C compressor via Econ mode.

My 2012 Ford Mustang would constantly cycle on and off. Once every 3-4 seconds. I'm pretty sure it was delivered to me low on charge or something. It should not be cycling on and off that much!

 

Yeah, I tried the ECON mode and, yes you can feel it go off.

I just came back from the office and sat in the driveway. Hmmm, says I. I wonder if I just turn the temperature up and watch the tach, I might be able to see the a/c compressor put a load on the engine. So I did that. Went on up the temp scale til the interior fan started up real high and started putting out HOT air (I turned the temp up to above 80*F ). Then I turned the temp button down, down, down and the high fan and heat stopped coming out and cool air came out. I did not notice a drop or rise in rpms when doing so.

Sorry, I'm too lazy to get out and open the hood and look at the compressor with a mirrior. Its over 100* today and I'm not in the mood.

You might try that. A/c on...........move the temp scale up til hot air comes out........look at the a/c compressor head to see if the clutch on it is engaged or not. Sounds good to me to try that.

Someone who knows will pile in here in a minute. Just wait.

 

That's exactly how I'd describe it. Even when the heater is on full hot, the compressor never turns off. It's odd, but I think it's normal on these cars. They must regulate the compressor in some other way...

 

I found this from a (very) unofficial source:

My ac compressor run all the time it does not cycle on and off on my Acura? - Yahoo! Answers

 

Confirmed - it's permanently engaged. From the workshop manual (for both 4.2 & 5.0):

 

BTW, the pressure relief valve releases excess pressure of what? Refrigerant?

 

It's part of the compressor, and I assume it vents refrigerant, since that's all the compressor handles. I also assume it doesn't do this routinely, but only if (for example) the system has been overfilled or there is a blockage that is causing overpressure.

 

Just to add a little here the AC compressor on most of today's automatic CC systems runs all of the time. The temperature is controlled by adding heat and reducing fan speed. Non CC systems usually cycle the compressor in older cars but even with those systems some still keep the compressor on and let you regulate the heat and fan speed manually. The principal of leaving it run is less wear on the compressor and belts. The newer compressors are more efficient and have less drag compared to their older versions. Consider driving down the road at say 70mph and have the compressor cycling . When the clutch engages it goes from 0 rpm to xxx rpm. As to the relief valve it will dump Freon if something in the system caused high pressure or if someone overfills the system.

 

That is interesting. I never realized how primitive my Mustang was with the A/C!

 

I just got the car back from the shop. They said they measured the refrigerant as they discharged/evacuated it, and said it was overcharged by a significant amount!

All is better now!