How do I know what refrigerant is in my system? - PeachParts Mercedes-Benz Forum

JHZR2 · #1 06-30-2009, 08:42 AM

Hello,

What is the best means of "sniffing" and characterizing the freon or refrigerant in an AC system?

My 81 MB has the original receiver/dryer, compressor, etc. When I run it, it blows barely cold, though the compressor does engage. I do not think it cycles though.

My concern is that there is a "quick connect" fitting on the low side of the system. If there was just a threaded schrader, I wouldnt be asking this... but the quick connect worries me, as it is indicative of an R134a fitting.

I have all records for the car, but I do not have any record of a recharge. The air blew plenty cold all last year - it has not lost enough to not engage, it just doesn't cool - maybe it dehumidifies a bit, but that is it. Still, if the PO did something stupid, like topped R12 with R134, I want to make it right. If it was a matter of simplicity to use the quick connect to do R12 (which may be illegal, right?), then I want to still make it right.

I have R12 and can top that, but I want to be definite. Is there a way to DIY this, or do I need to take it to a shop? Say someone did something stupid like top off with Freeze-12 or similar, how can I be sure that I account for this too?

Now, two other quick questions:
-the car is 28 years old and all original. Does it make sense to evacuate the system and do an "oil change" anyway?
-if I want to top it off, can I use my R134a gauges for R12? I know the fittings are correct to do this. Is there a set of best practices to purge either out prior to switching to the other refrigerant?

Thanks!

gmercoleza · #2 06-30-2009, 08:56 AM

I'm willing to bet that the R134a fitting is on there because the PO added R134a - why else would it be on there? You may never know. You're best off assuming as much.

#3 06-30-2009, 09:50 AM

I'm not willing to make that bet if it's my car. The consequences of being wrong are too big.

The only way to KNOW what refrigerant is present is with a Refrigerant Identifier. Any auto a/c shop will have one and can check it in five minutes.

If the car were mine, I would buy a filter/drier and maybe an expansion valve along with o-rings. I would then break the entire system down, thoroughly flush, put everything back together with the filter/drier going on last and not until I was ready with the vac pump. I woul already have removed the adapter fittings and added the correct amount of oil. I would then evacuate and charge with R12.

Even if you could use your 134 gauges, you should not do this. You should not let your gauge sets be contaminated with dissimilar refrigerants and oils. R12 gauges are very inexpensive. Much cheaper than a 134 gauge set.

JHZR2 · #4 06-30-2009, 09:59 AM

Thanks! The refrigerant identifier will tell me if I have a mixture?

compu_85 · #5 06-30-2009, 10:22 AM

It should, the shops use it to be sure what they're sucking out of a car won't contaminate their tanks.

-J

gmercoleza · #6 06-30-2009, 11:10 AM

Quote:

Originally Posted by LarryBible

I'm not willing to make that bet if it's my car. The consequences of being wrong are too big.

The only way to KNOW what refrigerant is present is with a Refrigerant Identifier. Any auto a/c shop will have one and can check it in five minutes.

If the car were mine, I would buy a filter/drier and maybe an expansion valve along with o-rings. I would then break the entire system down, thoroughly flush, put everything back together with the filter/drier going on last and not until I was ready with the vac pump. I woul already have removed the adapter fittings and added the correct amount of oil. I would then evacuate and charge with R12.

Even if you could use your 134 gauges, you should not do this. You should not let your gauge sets be contaminated with dissimilar refrigerants and oils. R12 gauges are very inexpensive. Much cheaper than a 134 gauge set.

What I meant was - don't assume it's R12. The R134a fitting means R134a was put in there at some point. But yes, obviously a MIXTURE is a definite possibility...

TheDon · #7 06-30-2009, 11:17 AM

Is there any sticker or plate notifying that the car was converted to R134a?

Arthur Dalton · #8 06-30-2009, 11:20 AM

With the conversion to R134a fittings and it worked well last year, the most likely diagnosis for your condition is a shortage of R134.
But to eliminate the unknown possibility of a mixture by anyone , I would simply evacuate , vacuum , and recharge with corrcect amount of R134.

Youi may even get away with a simple topping off of 134a, but a full vac would be best.

No one converted those fittings to r134 to put R12 in there, but they MAY have not vac all the R12 out.....
My bet is the car has been converted from R12 and simply has a slow leak.

JHZR2 · #9 06-30-2009, 12:41 PM

I have real doubts that it was retrofitted with 134a. Perhaps the pressure was "boosted" a bit with 134a, but that would be IMO, it. The PO told me that he had to "top up" the AC system so it blew cold, but that was it.

Thing is, my gauges are r12 and 134a capable. I would never do it, but if I was being lazy, I would potentially attach to a r12 bottle, and be too lazy to remove the 134a connection, so just screw on an "adapter". Poor practice, for sure, but my hope is that it was a bout of laziness...

r12 oil + r134a = acid formation, right?

Ill try to get this sniffed ASAP, to mitigate potential issues, and potentially open/flush and refill the system.

Nothing was opened, the car is like new (72k miles), all original.

Out of curiosity, any ideas of the cost to recover R12, flush, replace R/D, and refill with R12?

Thanks!

JHZR2 · #10 06-30-2009, 12:43 PM

Quote:

Originally Posted by TheDon

Is there any sticker or plate notifying that the car was converted to R134a?

No sticker. Likewise, no R134a connection on the high-pressure side. Im hoping it was the lazy solution to coupling the available gauge set to the available R12 can...

JHZR2 · #11 06-30-2009, 12:47 PM

The car, BTW.

My new 81 240D

#12 06-30-2009, 07:16 PM

AGAIN, there is NO WAY to know what's in there without a leak detector. If everyone followed Federal law which requires correct fittings for the particular refrigerant and a sticker with pertinent information then you would know. That said, I would be surprised if as many as HALF of the cars that have refrigerant other than original are properly labeled and have correct fittings.

If it were mine, I wouldn't even DREAM of taking any chances. I would sniff for leaks first if there's anything left inside. Then I would break all connections, flush all components, replace the r/d, add the correct type and amount of oil, evacuate and charge by weight with the original refrigerant type. BUT, that's just me.

JHZR2 · #13 06-30-2009, 10:06 PM

+1 I do not want to take any chances.

I know there is still a charge - the compressor engages.

I've heard that HC-based R12 refrigerants use a quick-connect. Unsure if HC refrigerants pass through non-barrier hoses like 134a...

I have an appointment for Thursday AM to get it sniffed and see what is in there.

If Im lucky enough to see only R12 (could HC refrigerants not be detected, should I worry about this?), Ill have the system leak checked, evacuated, vacuum pulled on it, then refilled by weight. Ill ask them to replace the schrader cores and add 1/2-1oz of oil to the system, then add the correct mass of R12.

If they see R134a, then Ill immediately have the system evacuated. Since I plan to use the car for the weekend, Ill drive without AC, and then plan to take it back in for R/D, full flush-out, re-oil and refill with R12.

It may have been a botched R134a job - certainly not a retrofit... Im leaning towards it being an HC or freeze-12 or similar job, which worked well enough, and worked for about a year (with still enough pressure now to engage the compressor). Im hoping that it was HC and that the HC diffused out... and so R12 will work OK.

Wish me luck!

Matt L · #14 06-30-2009, 10:30 PM

A standard refrigerant analyzer will detect R12, R22, R134a, other refrigerants including hydrocarbons, and air. Expect to pay something for this service, as the tool costs over a grand.

#15 07-01-2009, 08:33 AM

Your plan sounded good until you got the part where you said that if it is leaking that you would evacuate and drive it for the weekend.

Evacuating a leaking system and leaving the vacuum beyond a short time for leak detection reasons is a BAD plan. The vacuum will draw in outside air which contains moisture. The oil will absorb the moisture. Depending upon the particular oil, when moisturized it can create a terrible acid.

If you do have to drive away without the problem fixed, have them draw a vacuum then put in a leak charge. This will make a positive pressure and eliminate the possibility of moisture introduction.