Trying to diagnose 308 A/C charging issue..

What is the ambient temperature and what are the high and low side pressures reading while the compressor is engaged? What are the pressures when the engine is off?

TomB

 

For very rough numbers, at 80 degrees the refrigerant might be at 90 psi. Once a working compressor is started up the high side will go to somewhere near 200 and the low side will go down to maybe 30. If you start with 90 in the can, it will be drawn to the low side of 30. The low side has to be lower than the source for the transfer of fluid to happen. Again, these are very inaccurate numbers, for demonstration purposes only, but you get the idea.
If the high side isn't going up, and or the low side isn't going down, that would be a start to diagnosing what's going on.

TomB

 

Does it have binary pressure switch?
Are you using the gauge properly (not trying to be a wise a$$) but I assume you are using the yellow line to lead to lo-pressure side which requires opening the valve? Have you tried a cheapo direct single line to the lo-pressure side? BTW, did you evacuate the system before recharging?

 

Pressure in the source can is higher than in the car so it doesn't need to be 'sucked' in. It just flows in if there is a path through the gauge set. You may have a (common) stuck expansion valve. Needing a top-off every couple years doesn't mean a small leak, it's normal leakage. Since you don't do this often, likely you have forgotten a small procedural detail, like turning the freon can upside down so you get liquid and not gas.

 

May not have any bearing on the issue, but are you running any kind of particulate filter in the AC system? If the compressor is clicking on, but not drawing, there may be some kind of clog in the system. On another note, what kind of shape are your hoses in? Do any of them show any cracking or age? I have seen systems clog due to degradation of the hoses, where a clog will occur and block the flow of refrigerant even if the filter is new, or not installed.

You may also want to do a current check on the switches and solenoids related to the system. Sorry I cant tell you what current is good, and which is bad. What I will usually do is compare what I have in hand, to a new one.

Issue with that is unless you got the parts from a local parts house then you may not be able to compare yours with another one.

Hope any of that helps.

 

The pressure in the source can is only higher than the low side pressure if the compressor is working properly. If the compressor is not working the pressures will be equal. If the engine is hot the low side pressure could be higher then the can. Could be the system is full and and an additional charge will make things worse. Knowing the pressures would go along way towards figuring out what is really going on. Chrysler used to produce a great book with many different readings and what they meant.

Of course an evacuation and recharge with the recommended amount of refrigerant is always best.

And don't forget that as the system leaks through the years you're losing oil also, and that should be topped up as well.

TomB

 

My thoughts exactly.

I didnt post this morning because I wanted to confirm with our a/c specialist at work.

The first thing he said was "it may be a stuck or REALLY restricted TX valve (expansion valve)".

So I would recover the gas from the system, then remove the TX valve and inspect.

 

99 on the high side and 30 on the low side could indeed indicate a low charge. If the expansion valve was stuck shut the low side would be low and the high side would be high, as in the refrigerant is being compressed but has no place to go. If the expansion valve is stuck open the high side will be low because there is nothing keeping the pressure up.
I think you might be back to your original question as to why the system apparently not accepting juice.
This could likely be a problem with what ever you're using for hoses/connector valves. With the engine off you could connect the low side hose without the can on the end and slowly open the valve on the compressor. Refrig. should escape. This would tell you that you are connected to the system.

We await your next response.

TomB

 

Hope that was said in jest.

I use 30# cans and know from experience they must be upside down to exude liquid refrigerant, not needing the compressor to be on when doing so. That also how one overfills the system and a overpressure switch is in the system. The can's handles at the top are also stands so it can sit on a scale for precise measurement. Placed right side up and only gas escapes the hose which cannot overpower the system to fill it.

 

Gregg-
Disregard the high side for a moment- with the compressor spinning, when you open the valve on the supply can does the low side pressure change at all? It the set up is correct to feed more into the system the pressure in the can needs to be higher then the pressure in the low side.
The most useful thing to do once you figure this out would be to would be to evacuate the system and start from scratch. I believe that tool rental places will rent you an electric vacuum pump. Again, too much will do almost as much to performance as too little.
The theories here are really basic- solutions to AC problems usually follow a pretty logical path.
I agree turning the supply can upside down is a more efficient way to charge the system, and can more easily result in an over-charge, but you will eventually get the refrig. out of the can and in your car as a gas, it just takes a while.

TomB

 

Your TX valve can still be stuck or restricted, whether it was replaced 4 yrs ago or not. If there is crap in the system or a/c doesnt get used much it can stick.

I asked another a/c guy at work today and he said the though the same thing, a TX valve issue.

Obviously easier to diagnose with the car in front of you, but we all share the same thoughts on the subject so I would look there first.

But whatever man, just saying.

 

I'm wrong about something of value every day, but the expansion valve theory doesn't explain why he can't get the juice to flow into the system, which was the original question. If the pressure in the can is higher then the low side, shouldn't it go in?

TomB

 

Are you sure you punctured the seal in the top of the can?

YES, an unknown quantity of oil mixed with the refrigerant is lost [My lawyer made me add this next part] when you go to an certified ac shop to have your existing gas pulled with a recovery system. Newer recovery systems can add oil without having to open the lines.
OR NO Some will ignore the oil loss. I think that's playing with fire.
OR NO Some will add a back a small amount of oil. That's playing with a much smaller fire.

A few compressors additionally have an external non-pressurized crankcase reservoir which needs a fixed amount of oil. An oil volume stamped on the compressor refers to this and NOT to refrigerant oil...I can't speak to your specific Sanden compressor.

For a full start-from-scratch A1 driveway job, you must remove most ALL the oil. Using shop air, blow all remaining oil out of both hoses, turning the compressor by hand a few times as it will host much oil. Add oil. Then remove moisture and non-undesirable contaminants in the system by pulling an overnight vacuum. ReCharge.

 

I mostly agree. Unless you drain the compressor you never really know. For lack of a better plan, when removing the compressor is not practical or possible, I do add an once or 2 of oil.
It's a tough call. Refrig. recycling machines have a means to separate and measure the oil when you drain the system. However, you never know about past history such as how much seeped out with the leak.
If you have a vacuum pump, by all means start from scratch. If you've been losing and adding for a few years it would be nice to have a base line from which to gauge what's going on.
Besides, if you can evacuate the system then you know you're hose/fitting connections are good.

TomB

 

Heya mate, I will try my best to explain and to be a little more clear.

When you have a blocked TX valve, you can actually put a/c refridgerant into the system. I should have said that earlier sorry.

The needles wont move, which makes you think the a/c system is not taking refridgerant.

But, in fact it is. Refridgerant goes from the compressor, to condensor, to drier then onto the TX valve.

If you keep trying to fill the a/c system with refridgerant(which you think its not taking any, but it is) the refridgerant will reach the blocked TX valve and then start to "back fill" the a/c system with refridgerant which will eventually go back to the compressor as a liquid and you run the chance of 'lugging' the compressor, or blowing out the seals or actually damaging the compressor.

So............if everything is connected properly, the pressure in the freon can is higher than that of the low pressure side gauges, the can has actually been "punctured"................then I (and my guru a/c mates) can only think of a blocked/restricted TX valve as the problem Greg is having with the freon he is adding is not making his gauges move/system is not taking gas.

As suggested, I would recover the a/c gas. Remove the TX valve to inspect. It may be seized or have some crap in there. We have this issue at work all the time, TX blockages and some that seize also, but more TX valves with blockages.

Inspect/sort the TX valve, add 50ml of oil into the system then vac down and add the exact amount of freon needed for your 308.

Start the car, turn on the a/c and check its performance.

I hope this helps explain it a little better mate. It is A LOT easier saying it in person. I consulted my 2 a/c specialists at work again about this. I really only wanted them to help me try and explain it typing on the computer for you here.

 

Pap,

I'm with you.

TomB

 

Not a problem mate, I probably should have tried to explain earlier if it wasnt so hard to try and get across clearly.

It took me ages to type that post trying to word it correctly so it made a little bit of sense.

It may not be the issue, but sure sounds like it. Especially if there is nothing stopping the freon from entering the system.

 

Well everyone else has a theory....so i figured I'll chime in. Possibility one that the hose you are using is not opening the schrader valve far enough to charge the system....Possibiltiy two is that the valve-hose you are using is old and has "swollen" internally and choked off, preventing you from charging the system.....BTW both of these happened to me. I wound up going to harbour freight and buying a cheap set of gauges.

 

Both possible, of course.

But if you read post #10 and #12, I think he doesnt have an issue with the gauges being connected properly and working properly as he states the pressures change when he starts and turns the a/c off.

 

Ditto the business about the Schrader valve not being open far enough to charge. I have several cars that take R12. Two charge with no problem. However, the good old 328 had a valve that was not opening enough when the recharge fitting was screwed on. I ended up slicing a sliver off the rubber seal inside the screw on brass fitting. This enables the valve to be forced open a wee bit more and makes all the difference. It charges up nicely now.

Stay cool!