Oro

I found last weekend that a tiny little rumble at idle that had been perplexing me for a while was low freon in the A/C. It's good to check this since it can put undo strain on the a/c compressor and lead to replacing way before you would otherwise need to do so.

Since these cars have automatic CC and I don't drive it daily (she does), I had not correlated the two. the A/C worked perfectly and without fuss when I drove it, and I never turn it off "auto" like she sometimes does, and that would have let me realize it. Over the last year I have replaced a motor mount, new plugs, cleaned MAF and checked all air and vacuum lines and gaskets, etc. I have incrementally improved things but finally had this slight rumble/vibration you could feel with your hands on the shifter or wheel sitting still. Simply no reason for it unless something I did had broken so I kept following the mantra of "check what you last changed" (which is always a good diagnostic rule).

This weekend I did a motor flush and was changing the oil. While I was under the front with it running looking for leaks/checking my work/looking around in general, I heard the a/c compressor cycle and a low rumble. Duh. Should have realized this before. I then played with the car a while with the auto climate on and off and localized the rumble to that (keep in mind, it was very slight and would not register obviously if you weren't looking for it). The system was in fact low when I hooked up gauges.

If you want to check this, the photo below shows how. The High pressure port is in front of the alternator where the red hose leads. There is a sight glass bubble here - it is that circular window just aft of the brass hose coupling attached to the high pressure port. A cheap test is set your A/C to max low and then look at that sight bubble. If you see turbulent flow/bubbles in the oil/gas charge mix - you are low.

The Low pressure (fill) port is more awkward to get to - you stick your arm down between the torque strut/dog bone mount and shock tower brace and you will see a similar grey plastic cap; that is where the black hose disappears to.

DRACO A5OG

Good Call, it sure smoothed out my idle at stops

mmatheny

What year is that? '02-'05?? Man, what a crappy place to put the LOW pressure fitting! The one you use most!

Oro

Yes, it's a 4ES. It's not too bad - there is room to stick your hand down there once you sight it.

Oro

Follow Up: It appears easy to overcharge these systems.

I worked on tweaking it a bit more; it seemed to me it could use a little more freon as it was not quite "in the zone." Iadded more freon yesterday. Even at a normal operating pressure per most application guides and on my gauge, it was enough to shut down the compressor. I tried to get it up to 45psi while running at max cold, which given the 90F outside temp. was conservative IMO:

Charging pressure guideline:
http://acprocold.com/faq/r-134a-system-pressure-chart/

It was enough to trigger the pressure switch and disable the system. I adjusted the pressure downwards towards, when running, an indicated 35psi. Worked perfectly and a brief road test showed it putting out a 40F flow at Max Cold. Great!

So the lesson was don't trust the charts and/or gauges entirely. Overall I probably needed about 18/20 ozs to restore it to what appears peak efficiency. Afterwards we drove it home 50 miles in 95F heat (likely higher ambient given road heating/traffic). We RARELY get this kind of heat here - maybe 2/3 days a year - so this was an excellent test. The system worked effortlessly and maintained a cabin "auto" setting of 68 without working too hard from what I could tell. It was clearly working better and needed the added freon, but there was a very fine line well on the low side of the charging guidelines of just right/too much.

mmatheny

I always hook up high and low sides - it's hard to spot a partially plugged restrictor or other issue without having the high side readings, and a partially plugged restrictor or expansion valve will cause the compressor to short-cycle.

Oro

The high side was 215 I believe? Right where it should have been, IIRC.

steviet

Would a 'gurgling' sound after switching the engine off also be a sign of low freon charge? I am in Saudi Arabia, so run the AC on Max cold almost all the time......

Oro

That's not uncommon when running that hard. It's usually the system equalizing now that the compressor is off. Check your sight glass on the high pressure port with the a/c on max cold and see if there are bubbles. If it is not grumbling a little at idle when operating, and there are no bubbles, you are probably fine.