Air conditioning system over-filled?

[ltslimjim]

Gentlemen, how reliable are the gauges from auto part stores with the 'recharge kit' for AC compressor/system?

I tried adding Free-on to a system that had previously(2-3 years ago) lost about a can or two. The gauge was in the red as soon as I completely opened the can to begin 'topping off' the system.

I'm still a n00b. The car gets cool but not cold during the day in operation, with ambient temps of at least 80-85+ degrees. Could the system be over-filled? I didn't hear the compressor kick in/out like normal. I'm sure the o-rings etc are leaky, but the last I checked(ran the AC successfully) the compressor was working fine.

FWIW, this vehicle has a 4-cylinder engine and I no longer drive the car. Trying to help a relative get better cooling, when it used to cool just fine when I last drove it(1-2 months ago). Would driving the car help it cool better?

Any comments would be appreciated. Thank you.

 

[rshaw125]

You really need to hook up a proper set of gauges. Then you'll know the high side and low side pressures during operation. It could well be moisture in the system. A full evacuation and recharge is about $150. Plus extra if a few o rings need to be replaced.

 

[55Test]

I made the mistake of overpressurizing the A/C system on the 94 Civic I had a few years back. Something on the back side of the compressor popped and it blew a bunch of the oil and refrigerant out. The compressor would still run, but it would really drag the engine down, cut in and out at a rapid rate and made a bad squealing sound when it was running. I sold the car a month later.

 

[440Magnum]

The answer to your first question is "not very reliable at all."

But remember, even those cruddy little gauges are meant to read out LOW SIDE pressures and then with the AC system running. Low side pressures go UP when you turn the system off. If you just connected and opened the valve with the system off, the pressure *should* be in the red.

 

[mechtech2]

The gauges are generally reliable and accurate .
It is the implementation of them that causes problems, almost 100%!
How and when you read them is the key.
You can have a faulty gauge no matter how much you paid for it.

Specific help with your AC?
Then give us cold static readings, and readings at different ambient temps, with concurrent vent temp readings.

 

[ltslimjim]

Clarification: This is dealing with my now formerly owned 1999 Dodge Stratus I sold just recently.

It was about 85 degrees outside today. I have the different sized ports so it would be really hard to use the quick-disconnect type to the high side, the following image shows the low port at location 29(where I filled at) and the high pressure side at location 31. I have the 2.4L, if that helps.

http://moparestore.trademotion.com/moparImages/1999JA/i2114882.gif



More on this, I replaced the valve stem at the low-side service port 2 years ago, with A/C system running and lost most of the freon(of course). I turned the system off at that time, replaced the valve stem(which had become leaky and was why I decided to pull it myself, bad move in hindsight) and tightened it moderately in order to start installing new freon. Afterward, I tightened more until I couldn't hear air hissing or from the port and from my best estimate wasn't allowing any to escape, of course having the A/C system on max when doing this. Pressing in on the stem while A/C system is in operation allows for foamy like oil to escape.

I did use R134a type, a larger (2 can size) silver can advertising 'sub-zero' for 'better' cooling with a polar bear on the side(on top of a couple generic r134a cans when I initially re-filled). It came with a blue quick-connect/gauge. The larger can I used as top off(it was a partial from a friend, about 1 1/2 cans worth remained) and tightened it shut with the gauge still attached for a couple summers before trying it out today. From that point 2-3 years ago until now, I had no trouble with the A/C.

So, today I shook the can well and it felt like it had about a 1/4 remaining of freon. I proceed to turn on the A/C to max while engine was at operating temp and attach it to the low-side service port, after I completely opened up the can the pressure went from green to red(60+ psi etc). With the can closed it was in the green. Two weeks ago when I sold the car, I flipped the controls to 're-circulate' and it was cold that way(during the at idle 70 degrees outside), but this was after driving the vehicle.

I had received complaints from the individual that I sold the car to and was trying to help them out(being it was family).

It may be overfilled now, and I'll probably just recommend them going to a shop by the summer and having this work performed(evacuation, o-ring replacement and recharge).

 

[Chris142]

The low side guage that comes on the bottle may be reasonably accurate. Unfortunatly the low side pressures don't mean a thing when charging a system. You need high side pressure guage to get the proper charge.

So basically the low side guage on the can is useless except to check at what pressures the low pressure cycling switch open and closes.

Just another gimmic.

 

[ltslimjim]

^Wow, that's a great way of explaining it. It may need more freon after all. I don't believe I heard the clutch kick on. This was the first time I touched it in quite some time and it was not planned/last minute. I'll give it another go to see if I can add enough freon to have the clutch engage consistently.

 

[moklock]

+1 on having high and low side gauges.

The pressure readings also need to be taken with the valves closed and often at a slightly elevated engine speed. The vehicle sitting while charging for a long while without a fan or occasional mist on the condenser can throw things off a bit as well. Recovering and charging by weight is best when in doubt.

 

[ltslimjim]

Thanks for the tips. I'll try to get on this later, but may wind up recommending to pay a professional to get the system serviced and o-rings replaced, etc.

 

[mechtech2]

You can certainly fill a system with a low side gauge only.
You need temp sensors either way to get it really right.
Low side checks the static rest pressure at whatever temp, and also is useful for seeing a low condition.

r134a is not as tolerant of over filling as the old r12.

 

[440Magnum]

It sounds to me like the gauge is positioned so that with the charging valve closed, it (more or less) accurately reads the low-side pressure. But when you flip the charging valve open, there's some restriction in the hose or the quick-disconnect, so you're reading the pressure in the CAN of R-134a more so than the actual low-side pressure.

I've seen that even with some less-than-professional quality manifold gauge sets, or even with good gauge sets when the schrader-like valves in the quick-disconnect ports only barely crack open.

Is the compressor turning at all? Is the electric radiator/AC condensor fan running?

 

[ltslimjim]

I may/may not get a chance to look at this particular vehicle again, but it was blowing out cold air though I don't distinctly remember hearing the clutch on the compressor kick on/off.

If mechtech's proposal is correct the car may have been in the "green zone" still, if the gauge is really reading the can's pressure once it's filling the low-side service port.