Fix air conditioning using the kit in store?

In a properly equipped shop (like ours), we hook up the car to an AC "recovery" machine, that creates a strong vacuum (~30") to remove all air, moisture, old refrigerant, and oil from the system. If the system holds that vacuum for around

30 minutes, we assume there are no leaks, and recharge the system with the proper amount of oil and refrigerant. We then monitor the pressure to make sure there are still no leaks, and that the high- and low-side pressures are within spec with the compressor running. It's quite possible for an internal relief valve to stick, causing the pressure to spike to dangerous levels, or for the compressor to be faulty, and not produce the correct pressures in use.

Both lines might appear to go to the firewall for a newbie.

He needs to do as he was told earlier. He has found one port (high pressure) and that is the wrong one. He needs to find, unequivocally, the right one.

How do you get the oil out with a vacuum pump?????

You might want to try tracing the lines coming out of the compressor. One line goes to the firewall. The other doesn't. How simple is that? I thought my description was dead accurate but wadda I know?

I'd have to agree with you on that one, looks like you win. :-)

That's a good question. My guess is that the oil is simply sucked out in solution with the liquid refrigerant and that the recovery system recycles the old R-134A after separating the old oil and any impurities and replacing it with fresh oil and new refrigerant to replace any lost in our ozone layer. They may also disconnect the system at the lowest point and drain the oil directly if the system has lost all the refrigerant.

Just what I said.. BOTH lines end up at the firewall in most cars. The high pressure line goes through the condensor and to the evaporator, through whatever valves, and the low pressure line comes out of the evaporator, also at the firewall in most cases, and returns to the compressor.

If he has already found the wrong port, then it is almost a ringer that the correct port is in the other line.

It would be so much easier if we could be there and show him how to trace these.

You cant, totally, if you are converting from 12 to 134a.

If you have to change over to a new type compressor, you first wash the system clean. Then you charge the new compressor with the correct amount of correct lubricant. If you change the accumulator drier, you also estimate for that.

If you think you can live with the old compressor, there are ways to drain it (mostly).

Yes, there are ways to drain it but not with a vacuum pump. The vacuum pump pulls out gases, not liquids.

We have a wee bit of miscommunication here. I ain't converting from R-12 to R-134A. Are people still doing that in 2009? My post was not about changing the compressor or refrigerant either. My response was regarding the question "How do you get the oil out with a vacuum pump?" Do you know what the procedure for this is? My guess is that the refrigerant is sucked into a tank and that most, not all, of the oil is carried off in solution. Until an expert chimes in, it's all just a guess.

Sorry, I missed your point. :-) You're right, the vacuum pump pulls out gases. I have one of these pumps - the instructions recommend that the oil be changed every time a system is evacuated. Do people really do this?

No, if you pump the system down, the vacuum pump only gets a little bit of the oil. Most of it stays in the compressor.

If you want to actually remove the oil from the compressor, you pull the compressor out, turn it upside-down, and pour it out.

The only time you'd really want to remove the oil is if you were converting from R-12 to R134A, though, which is why folks made that assumption.

I don't claim to be an expert, but I have done a couple proper conversions and a couple half-assed ones and they all seem to have worked.

--scott

Answer is STILL, you dont.

My guess is that the refrigerant is

Listen, again.. refrigerant can be sucked off and compressed and recovered. Almost NO refrigerant goes with it. You can reuse the good refrigerant if you have such a system.

YES, you can drain the old compressor. There are instructions how to drain the oil , but you damn sure dont do it with a vacuum pump.

If the original refrigerant isnt screwed up ("black death"), dont worry about changing out the lubricant. It isnt normally done.

If the system is crudded up, you need to flush the system with solvent, replace the filter accumulator drier, pull a vacuum to remove the solvent, and recharge with lubricant. (This usually means that the compressor is bad and will be replaced anyway). Then you recharge with coolant.

Now, do you understand the process?

Above should read "Almost NO lubricant goes with it".

Sorry. This guy will drive a man to drink.

HLS wrote:

There have been many different colors of the 'security threat rainbow' regarding how much oil to remove and what is compatible since conversions came under scrutiny. Even though your question doesn't involve refrigerant conversions particularly, it's crux does generally follow the scuttlebutt around conversion dos/donts.

My feelings, after reading everything I can about proper A/C repair and performaing/monitoring repairs and conversions on many vehicles is this... It is best to remove as many lines and components as possible when trying to get rid of contaminated oil or wrong oil for the intended conversion. I have seen high dollar and normally very reliable compressors' bearings fail a couple years after conversion from R12 to R134a. Enough of these failures that I would not want to chance "saving" someone a couple hundred bucks to convert their system in the hopes that the compressor will survive. Most mechanics seem to be most concerned about A) their paycheck and B) getting cars out the door, so most mechanics will not concern themselves with doing the extra steps required to get as much oil out as possible. Same goes for most shop owners. Therefore the overwhelming advice seems to be that adding a polyester oil during a conversion (guess the amount or add the whole bottle; who cares, right?!) is a fine alternative to removing as much oil as possible and adding the correct weight and variety of PAG oil. It usually doesn't cause a problem. Sometimes it does. My experience and keen interest in this area has proven, along with much observational data, that this causes problems with the compressor in some cases. Like many things, it comes down to risk. I like to take as little risk as possible. Taking apart lines and blowing refrigerant/oil flush through as many components as possible (expansion valves and compressors don't qualify) isn't that hard, and can be easily sold to reasonable customers whom set aside proper funds to fix their cars.

Back to the basic question... neither evacuating nor vacuuming a system takes much oil out of the system. Some of the oil is refrigerant-borne, but the majority of the oil sits in the bottom coils of the heat exchangers and in the compressor sump area. Modern compressors don't really hold much oil either, and their respective systems don't call out for as much oil as older systems. All this means that the quantity and type of oil is really quite critical in maintaining a long lasting and fully functional A/C system.

Try using a proper AC machine, not a simple vacuum pump.

We have a slightly older version of this one:

Note line 4... " * Automatic Oil Drain " I have no idea *how* it does it, we just set the options, and let 'er rip. It sucks the system down, removes the 134 and stores it for re-use, extracts the oil (into the little plastic bottle on the side), and refills both the oil and 134 to the amount we specify.

That's pretty much the answer I was looking for. Thanks.

The folks assumed wrong. :-)

My guess was that most of the oil would be removed along with the refrigerant. Thanks for giving me the straight dope on this. Please excuse me if I misunderstand you - it sounds as if you are saying that the oil should be flushed out and replaced with fresh oil when replacing the compressor. Is it your experience that reusing the old oil is a common practice in this type of repair? That is interesting. Sorta like breaking in a new engine on used motor oil. :-)

Exactly...

If the system is old, and has had mechanical problems, I believe it is worth the effort to flush them with solvent until they run clean. Solvent shouldnt be used in the compressor, but you can flush the compressor with the lubricant oil several times and drain it.

Of course, I also think the accumulator, filter, drier should be replaced.

You do have to estimate how much new lubricant goes into the system, but as long as a person is judicious, I havent seen much problem with this.