924Board.org

[weisenheimer]

Bought R134a for a supposedly empty compressor. (no low side pressure or compressor oil drained when i put a hose on it.)

To my surprise, one 12oz can of 134a filled the line beyond 45 psi.... I had to drain it a bit, and I could only get in about 4 oz. of compressor oil!!!

Two tier question:

1. Does this sound right?
2. Is 4oz oil (give or take) okay?

If this is out of sorts, what to do?

[wdb]

if your filling an empty system, you need to put a vacuum pump on it and suck out the air that has gotten in to it, if you cant find the specs ( amount of freon system should have) you can try watching the tempeture of the air coming out of the vents( put a thermometer in the vent) as you get to the propper amount the temp will drop when you have put too much in you'll loose cooling ability and the temp will rise. you should check out vintage air's website http://www.vintageair.com/vintage.htm
it doesn't have 924 specific info but does have trouble shooting guide for ac and alot of other useful info. there a link to it in the links section under part suppliers

[dvarholy]

In order to convert over to R134A, you need to remove all of the old oil from the system. The original R12 used mineral oil, which is not compatible with the new synthetic oil. Check on the can to be sure. Also be sure to change out the filter drier as well. The proper charge weight for R134A will be different (less) than R12. Do not overcharge. You may still see gas bubbles in the sight glass even when the system is fully charged. Some compressors have compatibility issues with R134A, mainly the shaft seal and o-rings. It is likely that the air will not get quite as cold as with R12.

[gohim]

Sounds like you wasted the first can of R134a.

As the others have written, you must evacuate the existing air from the ac system, before you try to refill it with refrigerant. The primary reason why is because the system will not work properly with moisture in it. The existing air contains a large percentage of H2O, and the moisture will reduce the efficiency, and corrode ac system components.

The second reason to evacuate the air from the system is the system integrity test that is performed when the air is evacuated, and a vacuum is created in the ac system. That's how you check the condition of the seals in the system. A vacuum gauge is used to monitor the system, and if a drop in vacuum is noticed in 20-30 minutes, then the system has seal leaks that need to be addressed before filling with refrigerant, or it will leak out in a short period of time.

Converting to R134a requires the removal of the existing R12 compressor oil, which is not compatible with R134a oil. When the two make contact with each other, a gel like substance is formed which will plug the valves in the ac system. The ac system must be flushed, and the receiver/drier replaced (TWEEKS as a replacement Receiver/Drier listed in their catalog for only $20) because the drier contains a filter media, the composition of which depends on what the compressor oil used will be, and the filter media in the existing receiver/drier is already full of R12 compressor oil.

You also need to go through the ac system and replace the o-rings seals between the components. This does not cost much, or take much time, but is critical to the sucess of the conversion. The older seals used in R12 ac systems are not compatible with the R134a refrigerant, or R134a compressor oil. This will cause further deterioration of the seals. R134a gas particles are also smaller than R12 gas particles, and will leak from places that R12 did not leak from, so you will lose more R134a from the system faster than you did R12.

Legally you also need to install R134a High and Low Port Adapters when you convert to R134a. The conversion kits should have the right conversion adapters, if you purchase the correct kit, or you can go to NAPA, or Pep Boys and buy the correct adapter separately, if necessary.

To create the vacuum in the ac system, you can buy a compressor powered vacuum pump from Harbor Freight (regular price is $13, but they are or were on sale recently for $10). You will need a compressor capable of about 4cfm at 80psi. You will also need an ac manifold set to control the vacuum process, monitor the vacuum, and fill the ac system after testing. Harbor Freight had an R134a Manifold with the required hoses, and High and Low Port shut-off valves on sale for $60 (regular price about $80, I think).

R134a works at a higher pressure than R12, and less R134a is used in a system than R12. I think the conversion factor is about 80%. R134a conversions will not cool the car as well as the orignal R12 system did.

[ This Message was edited by: gohim on 2002-05-30 07:36 ]

[wdb]

you can use FR12 or 13 forgot which, but it is a replacement for r12 or 13, no modification of AC is necessary with the fr12, but It used to cost alot, dont know what the current price is. see the article for details What is the basic conversion procedure from R12 to FR-12?
To convert a properly functioning automotive R-12 system to FRIGC (FR-12), an installer must:


Recover and recycle the R12;
Evacuate the system ( for approximately 30-45 minutes);
Add approx. 2 oz. of Ester (POE) oil
Charge the system to approximately 80 to 90% of the R12 capacity and install the under-hood "system identification retrofit label".
Install retrofit fittings on the high and low side service ports;

It's that simple! In some cases, it may be necessary to adjust the cycling pressure switch on CCOT systems for optimum performance

http://www.refimax.com/products/fr12.htm

http://pacific.bizjournals.com/pacific/stories/1996/07/15/story6.html
detailed instructions
http://www.refimax.com/products/fr12_instructions.htm#charging

[ This Message was edited by: wdb on 2002-05-28 20:58 ]

[ This Message was edited by: wdb on 2002-05-28 21:29 ]

[ This Message was edited by: wdb on 2002-05-28 21:38 ]

[ This Message was edited by: wdb on 2002-05-28 22:42 ]

[weisenheimer]

But based on everyone's experience, do you generally use less than 12oz. of R134a?

My story is that the compressor was supposedly replaced when I bought the car, and it somewhat seems evident, since there was nothing but air in the low pressure line.

No oil, no nothing.

The A/C is working great now, but I just want to be sure that one 12oz can was enough, and that I don't have a huge "bubble" somewhere. I don't think that is the case if I am getting great cooling. (for an old 944 anyways ;-p )

[gohim]

No, 12oz of R134a is not enough.

I don't have the book handy, but it should need more like 28-30oz of R134a.

[kaffine krazed]

How are you charging the system?

[weisenheimer]

I am charging through the low pressure nipple on the compressor.

There are two ports located there, but one goes to the condenser, and one to the evaporator. I've filled the side to the evaporator. Its only taking one can of R134a, but when I bled the system, it acted empty.

I didn't know I had to keep a vacuum on for as long as some suggest, but how the heck could I not get more freon in.

Does the line have such a potential to create its own vacuum that releasing the pressure would not eliminate the "pockets of air"?

[Mich924S]

I just had my AC charged on my 87 924S and I was told they added 2.5 lbs so the capacity(at least for the 1987) is at least 2.5 lbs

[gohim]

wdb,

FR12 (aka Freeze 12) is nothing more than a blend of R12 and R134a. That's why the compressor oil for R134a is used with it.

[gohim]

The amount of compressor oil, and the type of oil in an ac system is critical to the life and performance of the ac system.

Too much oil, is as harmful as too little oil, and the wrong type of oil is always eventually fatal to the system.

Since you don't know how much oil is in the system, and you are converting to R134a, and the system does not appear to be operating correctly, I recommend that you evacuate the R134a, dump all of the oil, flush the system (they sell chemicals for this purpose), replace the o-ring seals with R134a compatible seals, replace the receiver/drier, pour in the correct amount of oil for a dry ac system, evacuate, check for leaks, then refill with the correct amount of R134a (if that is your choice of refrigerants).

The Porsche Factory Workshop Service Manuals, AS Service Section, should list the total amount of oil required, and break down the amount to be added if a single component is being replaced.

You never mentioned that the ac clutch is engaging, or the High Side Pressure. When the ac clutch engages, the compressor is being driven. Then the low side pressure should drop as the available refrigernat is compressed and routed to the evaporator. When you don;t have enough refrigerant, after the ac clutch engages, the Low Side Pressure will drop so far that the Low Pressure Switch will engage, and the power to the ac clutch will be cut. When this happens, the compressor cuts-off, and the Low Pressure will rise to a point about the Low Pressure Cut-off, and the ac clutch will engage, causing the same action to repeat. Normally, when filling a system that has dropped below the minimal pressure and tripped the Low Pressure Switch, what you can do is bypass the low pressure switch by jumpering the two wires leading to the switch together. This is engage the ac clutch, powering the compressor, and allowing the system to draw in more refrigerant. Once 1.5-2.0 cans of refrigerant have been added to the ac system, there should be enough refrigerant in the system to remove the jumper from the Low Pressure Switch, and allow it to work normally.

[ This Message was edited by: gohim on 2002-05-30 14:58 ]

[AznDrgn]

It is not neccessary to change out the filter dryers and the O-rings for the system to work, it is nice to do but not absolutely neccessary. Gohim is correct on the point that you need to evacuate the systemt before charging it and the oil needs to be added in the correct proportions. However the part about bypassing the LP cut off I reccomend not doing unless you know what you are doing. If you evacuate the system there should be enough vaccume to pull in a can or two of refrigerant and the from there the compressor may cycle on and off til it has sufficient pressure to get by the LP cut off. As for the exact amount you need to use there is normally a sticker somewhere under the hood that should tell you, but most likely that is gone so I'd say check the haynes manual or call porsche and ask. It'll be in pounds and ounces so you just add up the weight of all the cans of refrigerant (eg you need 1lb 4oz you use a can of 20oz).

Hope this helps

[gohim]

If you fill the ac system with the same amount of R134a as the system was designed to use of R12, you will be seriously over-charging the system. R134a runs at a higher pressure, than R12, and when filling with R134a, you are supposed to fill with only about 80%-85% of the R12 charge.

When a car is professional converted to R134a, the technician is supposed to calculate the new charge weight, and record it on a sticker under the hood that warned that the system is filled with R134a.

When you use an ac manifold gauge set to fill and monitor the ac system performance while you are filling it, you don;t need to know what the recommended refrigerant charge is, because the gauges will indicate when the correct amount of refrigerant is in the system.

[ This Message was edited by: gohim on 2002-05-30 15:04 ]

[weisenheimer]

Guys, you are pretty awesome and I appreciate all your help...

Help me a little further and lets "speculate".

My system is holding at 45PSI on the low pressure side, but again, I only put in 12oz, but when I evacuated it was just air (not using a vacuum though)

Its cooling fairly well (I can tell because I live in NC ;-p ), so why would it do so at only 12oz of freon?

From what I've read if its too much or too little (given the low pressure switch is closed with enough pressure) it will not have any noticable cooling results.

What has happened?

Possibility #1: I thought I bled everything out, but there was a vacuum of freon at or near the evaporator, and the system has finally been regulated with my addition of freon and oil?

Possibility #2: Has a pocket of air moved from one end of the system to the other, whereas the Freon is pushed ahead of the line (wherever it goes - I dont understand it all) and there is air behind pushing it through the system?


I'll be honest, if I knew that it had to be evacuated with a vacuum, I would have bought that $15 pump... now I am just trying to save from having to buy a few more cans of freon, and the pump for this round.

Thanks again for the help,
RJW