Hi everybody
I know there are already plenty of AC threads. I tried to digest the information from them to come up with a plan for my car's AC. I'd appreciate it very much if you would comment on this approach.
My car's (1992 300TE 156kmiles) AC system stoped working about a month ago: the compressor just does not engage anymore.
The AC's performance has been degrading somewhat before that moment: At idle there was hardly any cold air coming from the vents. And there was a whining high pitch sound, a bit like a jet engine from the compressor whenever it was engaged.
The system is original and untouched.
I bought pressure gauges, two cans of R12 and a leak detector. So first I wanted to check whether the compressor stopped due to low pressure by bypassing the pressure shut-off. If that's the case, I planned to add the necessary amount of R12, assuming that it just leaked gradually over the last 12 years (there is residual pressure in the system, I hear "pss" when I open the schrader valves for a short moment). Then I would scan for leaks. If there is one I'll have the system evacuated. I'll then repair the leak (if it is not the evaporator) apply a strong vacuum to boil the moisture and recharge (of course with R12).
If the compressor is shot I'll probably need to evacuate and flush the system, install all necessary new components and recharge.
Does that sound like a good plan? BTW is it absolutely necessary for the compressor to run when topping off with additional refrigerant?
Many thanks, Bruno

__________________
_
1992 300TE 160 kmiles

I just got a 1992 300 TE with 134K miles, which had previously been converted to R 134a by an MB dealer. The system does not hold gas, obviously it has a leak somewhere. I put about a 1 lb in and 3 weeks later there is not enough pressure for compressor to kick on.

I've tried to find leak with my sniffer with no success.

My plan and I think this would apply to you too would be to rechange and add dye and then try to see if I can find the source of the leak.

I have another 1992 300 E and I replaced the compressor, expansion valve, reciever dryer last year. The compressor on that car was worn out and leaking. I hope that's the case with the 300 TE since I don't want to have to learn how to put in a new evaporator. The 300 E had a new evaporator installed before we bought it about 8 years ago when I had only 60K miles on it. That car now has about 126K miles pm it.

I think it best to add gas with engine running. If there is not enough pressure to do this you can add a little with the engine off and then turn the compressor by hand a few times to move the gas around a little. Do try to fill with the engine running.

Hi Bruno, dave Rose here... Besides you adding additional refridgerant, its important to add some oil into the system also. See if you can get a hold of a can of R12 with the oil in it already. If not, they sell oil thats mixed with enough R12 to introduce it into the low side of the compressor. When filling, dont tip the can, let the suction side slowly pull the new gas in. All leaks usually end up with some oil being released out from the system. If you do plan to service your ac system, first tighten all of your couplings where you can find them, and inspect all hoses for tell tale oil seepage. Its also a good idea to check the flange fittings on the compressor as well. Make sure you get the right oil for your R12 system, the newer PAG oil for the 134 type systems will ruin your compressor.

Thank you for your sensible comments!
Dye is more reliable (no false positives), is it not? But then, I believe I need a special device to inject the UV dye, or how is that done? Sorry for those beginners questions.
BTW, me too I do not feel like doing an evaporator job...
dave Rose, I'll follow your tips. If the system needs only a little (let's say about half a pound) of refrigerant would you still add oil?
Many thanks! Bruno

__________________
_
1992 300TE 160 kmiles

they are not too expensive. Thanks again, Bruno

Since my system was not under pressure I just removed the service connector and put in one capsule, i.e., .06 oz of dye and 1.5 oz. of PAG 46 oil.

My sniffer seems to detect freon at evaporator drain outlets under car, driver's side more than passenger. I don't know if the dye can leak out there to confirm location of leak.

(PAG 46 OIL ok, user has R 134a retrofit)

http://autorefrigerants.com/co00033.htm
This link will get you to where you can purchase direct R 12 equivilant drop-ins, without the need to flush your system. I would recommend full evacuation by a HFC recycler, and do a good one hour evacuation before you add their oil and substitute refrigerant. If you can get R12, thats fine, but they are getting up to $60.00 bucks for those little cans. I remember the days when Strauss Stores sold a can of R12 with a filler kit, for $3.99.....

Thanks for the link, Dave Rose. I also found a loooong thread on the forum with heated discussions about R-12 alternatives. Based on what i read I will first see whether I can top off with R-12 (no leaks in the system). In case I'll need to change components that require an evacuation I'll probably switch over to a hydrocarbon refrigerant. The main advantage I see is that they do not react with residual moisture to form aggressive chemicals (so pulling a deep vacuum, not trivial for a DIY, becomes less critical), they are cheaper and environmentally safer. Their seem to cool very well too.
Bruno

__________________
_
1992 300TE 160 kmiles

Don't forget to mention that they are also illegal for use in mobile AC equipment. Also don't forget to change the service fitting on your AC system so that in the future a tech does not recover your propane into his 50 lb cylinder of pure R12 and lose $500 dollars worth of refrigerant. Of course thats the "best case" scenario - he could also not discover that his R12 supply had been contaminated and proceed to dispense a contaminated and illegal mix of hydrocaron based refrigerants in his customers cars.

Pulling a deep vacuum is a trivial task if you have a vacuum pump and a A/C system that is not leaking - pumps are available for about $200 new and they can be rented at many rental shops for $10-15.

Bulk R12 is now under $10 a pound on e-bay and 12 oz cans sell for $15-30 dollars per can. You can recharge your system for a total of $30-$60 - is it really worth it to mess around with HC based refrigerants? It's amazing to me that somebody can take the time to do the research on this topic and come away with the conclusion to introduce anything but the correct R12 into their system.

I'd also like to disagree with Dave regarding adding oil to a system that has a small leak - my service literature does not recommened this procedure and I've never added ANY oil when topping off A/C systems in cars. My A/C recovery equipment has an oil seperator with a sight glass bowl that shows how much oil has been removed during a recovery operation - the amount of oil removed in a total evacuation, as best I can tell, is about 1/50th of an ounce. The oil does not mix with the gas and for the most part it tends to stay in the system unless you have a massive leak.

Good luck - Tim

Tim
It is not illegal to use in MA. It is however again the Clean Air Act if I replace an ozone depleting refrigerant. It is legal to replace R134a however.
No tech will touch my car and I will keep it as long as it lasts.
Pulling a strong vaccum might be easy with a good pump, but the loaners I have seen were in very poor condition. I am reluctant buying a new pump - I'll leave the country and would then need a 240V version. Versions that can use both voltages are 450$ or more.
I am not concerned about safety: less than 1lb of hydrocarbons are no big threat in the very unlikely case of a fire. It is certainly way much less energy than 20 gallons of fuel.
But let's see, I do have not decided yet. If I find a place with good loaner pump I will stay with R12. (Anyway I would have to convert to R134a first in order not to violate the law.) It is just hard for me to understand the polemic against the hydrocarbons.
Bruno