AAAARRRRRRRGG. Summer's here, I love it, but my W124 does not. The 88 300CE A/C is simply not doing the job. It was conmverted to R134a last Aug 04 by the previous owner because his compressor went south. He replaced the compressor, receiver/drier, flushed the system, and the work was performed by a reputable A/C shop. I've had the car for about six months now, no problems wharsoever, except for the air. Last week because the temp coming from the center vent into the cabin was only slightly cooler than the outside ambient air, and the aux fan was never coming on with the air running, I brought it to my local A/C guy who has served me very well in the past. He recharged the system, but said not to expect much improvement. The fan does cycle off and on now at the correct pressures from the receiver/drier switch. The car runs at 90 - 100 degrees with or without the A/C on, and the fan has not kicked in because of high sensed temperature. He also said that in his many years of experience, Benz's as a rule do not like to be converted, and that the biggest problem generally was the undersized condensor doing a poor job exchanging the heat from the hotter running R134a vs. R12. He also said that there was an improved condensor available from the dealer which should be installed when converting from R12 the R134a. So may questions are:

1. Is there such a factory condensor, has anybody tried one on a converted w124, and did it help?
2. I know there are aftermarket parallel condensors available; would one of these help? Realize there will be some plumbing alterations necessary, and I should use the biggest condensor I can fit in front of the radiator, but it is worth it?
3. My 190E's are still use R12. My Jeep MJ too. All cool well in the brutal 'Bama heat with no problems. Should I just reconvert back to R12 on my 300CE and restore the system to operate the way it was designed for? Probably be cheaper in the long run. All comments and suggestions from the experts on this great forum are much appreciated. Don

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93 190E Sportline (RIP) (45K)
92 190E (Xferred most Sportline parts to this body)
88 300CE (71K)

And the Jeeps:
01 2WD Cherokee XJ (35K, Mama's grocery/kid hauler)
91 4WD Comanche (300HP stroker)

You could reverse convert to R12 cheaper than using a bigger condensor. R12 has gone WAY down in price and is the stuff that will give you the cool air you want.

Good luck,

If the compressor went south I hope they cleaned the entire system VERY well, as metal particals from the compressor failing could have been sent through your system. It probably worked for a while and then either clogged your system or damaged your new compressor. Need to check pressures and tempratures on your system to give you a better idea of whats exactly going on. But from your description "the aux fan was never coming on with the air running"

This fan has to come on when your compressor is runing for your system to work properly. Your compressor compresses the freon GAS turning it into a high pressure superheated hot GAS, as it goes through your condensor the aux fan cools this GAS and turns the freon into a warm high pressure liquid. You should be able to see this liquid from the site glass on the dryer. This warm LIQUID freon goes through your dryer where your low pressure and hi pressure switches are located. The low pressure switch shuts off the compressor (meaning you have a leak or lost your freon) the Hi pressure switch turns on you aux fan. If your fan is not comming on then you either do not have high enough pressure (225- 300psi depending on outside temp) or your fan switch or wiring is bad. The warm liquid froen goes to the expansion valve where the magic happens. When the warm liquid freon passes thru the small opening it converts back to a gas. (This process is hard to explain and understand as this process absorbs heat and does not produce cold but that is a biproduct of the chemical reaction.) The cold freon gas circulates through your evaporator warm air is blown across the coil and absorbed thus you have cooling and condensation from removing moisture in the air. The longer this chemical reaction takes place then the low side LIQUID freon line starts to sweat, the low liquid freon line starts turning cold with moisture from the expansion valve sometimes all the way back to the dyer. After the freon GAS leaves the evaporator it is sucked by the compressor where you will not have pressure but a vaccum. Then the cycle starts over. Hope this wasn't too long.

If your mechanic is telling you that 134a wont work on your Benz he is wrong. It will it's not as cold but it will work. I would go to a different AC guy and get another opinion. You do have a system failure if your aux fan is not comming on when your compressor is running.


I converted my 260e to 134a and it blows cold. I had several restrictions in the condensor. I had to remove and flush for about an hour to get all the dark brown oil out of the coil. Flushed the evap without removing, flushed all the lines, replaced the dryer, expansion valve and all of the o-rings. I flushed with laquer thinner and shop air in my garage. I also left the condensor out in the sun on my driveway for about an hour so it would heat up and be easier to get the old oil out.

Pulled vacuum for an hour, oil and charged 134a, Blows cold 35 - 40deg out of vents on 99deg. day.

I think 134a works ok and 12 was colder but 134a I can do my self and save a bundle. Only cost me 125.00 parts


Good luck

Anthony

Thanks you very much for the replies. When I bought the car the original owner furnished all maintanance records from day 1. The detailed bill on the conversion states the compressor, resceiver/dryer and all O-rings were placed, and included a system flush. But he was only charged for two cans of R134a. Looking back through more service bills show the mono valve was also changed in Jun 00. Several of the service bills are hard to read, but there were multiple R134a A/C charges earlier than that; one bill states that the system is mixed. But it was always charged with R134a. I think the car was never converted properly, can not find anything stating a complete evacuation and flush for the system.

I have tested the aux fan by shorting the two wires on the pressure switch; the single fan runs on low speed as it should. Also from the temp switch on the head, fan runs at high speed as it should. The mechanic states that after he charged the system, the fan did cycle off and on at the correct pressures. Machine man, my guy didn't say the R134a would not work, just that it will not get a cold or run as efficiently in a Benz as the original R12. So, as Larry suggests, I'm going back to square-1 and reconvert back to R12. The system is unsat now, there are bubbles in the site glass, and I'm unsure of what is in the system. I think this is the best course of action now. At least this way I'll know what I'm working with.

__________________
93 190E Sportline (RIP) (45K)
92 190E (Xferred most Sportline parts to this body)
88 300CE (71K)

And the Jeeps:
01 2WD Cherokee XJ (35K, Mama's grocery/kid hauler)
91 4WD Comanche (300HP stroker)

Learn something new every day

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1989 300 SEL that mostly works, but needs TLC

The expansion process is not hard to explain. Evaporation is a cooling process. When the high pressure gas passes through the restriction of the expansion valve into the low pressure area it causes evaporation. Evaporation being a cooling process, cooling takes place.

Have a great day,

Another way to describe what happens: the liquid r-134-A boils at a certain temperature, depending on the pressure it's under. At the pressure on the high-pressure side, it condenses to a liquid as its temp falls to condenser temperature (around 100-150 degrees F). The expansion valve is simply a restriction, whcih separates the high-pressure (condenser) side form the low-pressure (evaporator) side. The boiling point of the liquid R-134-A falls dramatically at the lower pressure; it boils in the evaporator ('evaporates') at a nice, low temp, which provides the cooling to the passenger compartment by absorbing heat from the evaporator coil (the evaporator is basically being heated by the air from the passenger compartment which is blown across it's fins by the A/C blower).

This boiling of the liquid R-134-A explains why it is liquid in the can, but becomes a gas (and gets cold) when the can is punctured. The can has a good bit of pressure on it. If you heat the can enough (don't), it will boil in the can, and Kaboom.

I would never convert a car...

But I've heard of ppl relaying the aux fan to come on with the compressor.
That makes a big improvement and might make you happy.

Do you live in Huntspatch?

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

R12 is available by the boatloads on ebay, pickup your CFC license like many of us have and buy it at the price you desire.

134A will not find its way into any of my vintage autos ever, there is so much around it's not even funny.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

It takes more 134 (lbs/hr) v. 12 to provide the same cooling effect. All things being equal, the same compressor must rotate at a higher rpm for 134 v. 12.

The consensus is to reconvert back to R12 - my original plan. Love everything about this coupe, except for the present A/C. Thanks to all for the great advice. Larry, you said install a larger condensor when reconverting back? If I'm going back to original, why? Realize the 124's were not world beaters with the OEM A/C as far as freezing you out, but I'm just looking for adequate cooling at or near original specs. 'Bama summers are brutal...........

Go Tide

__________________
93 190E Sportline (RIP) (45K)
92 190E (Xferred most Sportline parts to this body)
88 300CE (71K)

And the Jeeps:
01 2WD Cherokee XJ (35K, Mama's grocery/kid hauler)
91 4WD Comanche (300HP stroker)

Did reconvert back to R12 and it made a huge difference. Almost back to original cooling specs, and am happy. But not completely. I still have the problem of the aux fan never kicking in when the A/C is running. When I jumper the high pressure switch (I did replace it) the aux fan runs at low speed on my 1-fan 88, and the A/C runs cooler, but I know the jumper is just a band-aid. I would like to wire the fan so that it cycles on and off with the compressor, and leave the temperature switch on the block intact for high speed aux fan running. I know I'll have to tap into the compressor clutch circuit somewhere to trigger a relay when the compressor comes on. The relay will apply a ground through the contacts to run the fan. Is this the best way to go about it? On every other newer vehicle I have the aux fan runs when the A/C runs, including my 190E's. Has anyone done this, and are there any cons by doing this? And if anyone has a wiring diagram that would be great too. Thanks as always for the great help.

__________________
93 190E Sportline (RIP) (45K)
92 190E (Xferred most Sportline parts to this body)
88 300CE (71K)

And the Jeeps:
01 2WD Cherokee XJ (35K, Mama's grocery/kid hauler)
91 4WD Comanche (300HP stroker)

Does this go for a 1977 and a 1980 240D
Thanks,
JT Treeman

Yes, R12 is nearly the same price as 134A now.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]