Recharging A/C system....question

[eddie1278]

An A/C system will in fact get low over time even if no leaks are present in the system. Anytime you have a rubber hose or o rings refrigerant will very slowly permeate through it even though it doesn't have holes in the rubber. Rubber itself is not completely non porous.

[Blue biker]

Originally Posted by Joe33

Cant charge by pressure in an auto ac. It varies constantly.

It varies according to ambient air temp and state of charge, I have a 2005 Jeep at an ambient temp of 70* the low side should be 26-35psi with a high side 180-240psi and a center outlet temp of 27-38*F.

At 90* it's 44-53psi low side 250-300psi high side with at temp at the center outlet of 43-55* so while pressure may vary relative to ambient temp it can be a good guide to state of charge.

Back in the day it was simpler when cars had a "sight glass" on the receiver drier and if it had bubbles it was low, if it was clear it was full, or empty.

[snebarekim]

Originally Posted by dfour

OP here. I temporarily jumped the relay so that I could add a 12 oz can of refrigerant.. Pressure probably wasn't all that low to begin with. Shows 36 lbs after adding the can.

Compressor clutch still won't engage on it's own. Obviously something still wrong. Here is my next question regarding the attached picture. Why is there so much frost on the a/c line near the firewall?

Originally Posted by Joe33

You see frost there because there is an orifice in that line that meters the refrigerant.
You are probably still low. Or the orifice tube is clogged.
Generally the compressor wont kick in until the pressure exceeds 60psi so I would go for low freon based on what you are writing.

What Joe33 said here.

Dfour, what does the sticker under your hood say as far as refrigerant charge weight goes, and how many cans of refrigerant did you add?

[Don in Austin]

Originally Posted by Listener2307

You can't?
You can't watch the low side pressure, which varies quite a bit when the system is low, and stop charging when the low side system settles in at 40 PSI or so? That doesn't work?

Not very well. Variables include:

Compressor design
Humidity
Interior temperature of the vehicle.
Outside air temperature
Sun load
Engine RPM
Orifice tube or expansion valve design
Front only system or front/rear

For many modern systems 40 PSI is rather high.

Do people get away with this highly inaccurate method? Sometimes. But, on a regular basis my
shop sees cars where this has been tried and a proper evacuate and recharge gets the AC working again.

Don in Austin

[dfour]

Originally Posted by snebarekim

What Joe33 said here.

Dfour, what does the sticker under your hood say as far as refrigerant charge weight goes, and how many cans of refrigerant did you add?

Here is a picture of the sticker. Looks like 1.6 lbs for a pick-up. I added (1) 12 oz. can of refrigerant.

Also, when I attach the A/C gauge to the low side port, refrigerant sprays out until it's connected. Requires me to be quick with a good amount of pressure getting it on. Probably normal??????

[snebarekim]

Originally Posted by dfour

Here is a picture of the sticker. Looks like 1.6 lbs for a pick-up. I added (1) 12 oz. can of refrigerant.

Also, when I attach the A/C gauge to the low side port, refrigerant sprays out until it's connected. Requires me to be quick with a good amount of pressure getting it on. Probably normal??????

Losing a little when you connect/disconnect your hose is normal, just try to be quick.

Now, as others have stated here, if your system was completely discharged when you began, there is:

1- A leak for sure.
2- A good chance of air being in your system now.

Since you seem to want to try a DIY fix at first here, I would add a second 12 oz can, since your system was pretty flat to start with. 1.6 lbs is nearly 26 oz.

Making sure the can is warm when you start will help it flow into your system. Since by your photo you posted earlier I see you do have a suction accumulator, it is OK to turn the can upside down to introduce liquid.

As you add the second can, you may have to bring your engine revs up, which should drop your suction pressure and assist getting the refrigerant into your system.

While you are charging it, watch that frostline on your liquid line, it should disappear slowly.

When the can feels empty, disconnect.

If there is air in the system, this will screw up your pressures some, as air is non condensable (and contains moisture).

With the second can in, it should run without the LP switch jumpered. The LP switch could be as low as 40 PSI to close.
If you still have the frostline on your liquid line after adding the second can, and letting it run a while, then you may have a restriction at your metering device (the connection in your photo where the frost begins). That is a different problem.

If no frost, I would suggest you then go look for the leak. Apply soapy bubbles such as water with dish soap in it, at all the obvious joints and connections. Don't forget to check both low and high side valves where the hoses connect. Finding the leak will give you an idea of what to replace and/or fix if you decide to repair it correctly.

If the system was completely flat when you started, the presumed air in the system will certainly prevent it from running at 100% efficiency, and adds load to the compressor, FYI.

Hope this helps.

[ovi8]

The dyes that they put in to detect leaks... does that wear off over time? We had it done to 2 cars and after 1.5 years the AC stopped being cold again and they didn't see anything with their special glasses...

Is that dye only useful if we went back after a few weeks of AC use?

The dye is only like $15 to add so it's not like they're trying to rip us off - if anything, finding a leak would give them more work to charge us for... but... no leak.

Originally Posted by eddie1278

An A/C system will in fact get low over time even if no leaks are present in the system. Anytime you have a rubber hose or o rings refrigerant will very slowly permeate through it even though it doesn't have holes in the rubber. Rubber itself is not completely non porous.

It took over 5 years for this to happen to 2 cars, then only 1.5 years after a recharge and again no refrigerant - seems too quick for it not to be a leak right?

[wheelsup]

If no visible leak it might be in the evaporator. That is where my car was leaking.