Air Condition Question

[boblez]

i have a 300CE 1991 (is that a W124?) Anyway aircons not getting cold so went to local dealer who told me that as it was an old car id have to have the aircon replaced!

Anyone know how true this is? If it isnt any ideas where i can get it regassed without changing the system?

Thanks in anticipation

 

[mlc]

Boblez,

not sure i'd venture anywhere near the dealer with a 13 year old car. They will just see pound signs flashng before their eyes!

I cant see any reason why just because its old it needs replacing. Assuming that they didnt actually look at the car I think they are just putting you off. A quick look in my local yellow pages (manchester) has a full page of car aircon specialists. Check that they have knowledge of your system before letting them loose on your car. Finally prepare for a hefty bill. Expect them to charge at least £100 to re gas the system without any repairs, if you have been running the pump without gas it could easily be damaged as the gas is the lubricant. The regassing charge will probably still stand even if they find an expensive fault which you chose not to repair.

Good luck.

Mark.

 

[CoventGardenCabrio]

Yes it is a W124. And I agree with the previous reply, although a London specialist (the much-praised George Fraser) quoted me £50 for regassing today.

What they would normally do is regas and then see if there are any leaks in the system. If there are, then it can get quite a bit more expensive.

Good luck!

 

[nickh]

ahh, I have been through this before.. I have a 1992 w124 230e with Aircon..

I strongly suspect the following.

The Air con would have fitted by an expert after the car was sold new as i understand MB did not fit it as a factory option from new at this time - not till 1994-95 onwards..

Also it would be a r12 system as mine is, you have several options..as r12 gas is now illegal..

1. get some one to regas & clean the air con system and replace with a drop in replacement gas (eg r24).. this is the cheapest option will take several hours and cost around £100 (i had this done & works fine)

2. convert to a r134 system, new seals in compressor & pipes & condenser & drier etc - bit more expensive & takes longer means you can get it recharged almost anywhere..


problem is i,m told you cant simply regas the system as you need to expell all the old gas as you cant tell how much gas was in there in the first place, then depending on compressor model they will top it up to 90% of the original charge..

anyway hope it goes well..

 

[Apial]

Sorry I can't agree with you re a/c not being a factory option until '94. My 300CE-24 had it fitted from new in '91. The car takes 1.1KG of R12, so 990g of R49 will replace it. The whole process including toilet breaks will take less than 60 minutes and cost about £85 for a home visit.

If your car has been stood for a year or two, you can expect the r12 to have leaked past the compressor shaft seal. They are a daft design, but that is the only way to do it. Just keep the a/c running for 10 minutes a week and the seal will not leak again. In the winter you can run it on demist instead.

Just to be sure, you will have a yellow sticker on the front edge of the engine bay, and it will tell you how much R12 was originally in it. Mine was 1.1KG.

I wouldn't bother converting to R134a. If the mineral oil from the R12 system mixes with the synthetic from the R134a it will block up the system. Every seal will have to be changed as R134a will destroy the originals. Some condensors have to be replaced with a larger one. I don't know if a 3 300CE will, but it it is not worth it. R134a also runs at higher pressures than was originally intended for R12. There is no shortage of places to get more drop in refrigerant, so there is no real disadvantage to having it compared to R134a.

My R12 dropped to 80g with no damage caused. I didn't have a leak, just a temporary leak due to the compressor not being used for 2 years. All is running 100% now with vent temperatures at around 7C.

Boblez, yes, a 300CE is most certainly a W124, and probably the best looking W124 shape, if not best looking Mercedes!

 

[Geoff_Slade]

Gosh we've got a wealth of technical knowledge on this forum which is why it's so good. I've learnt more reading this post than I've learnt from the manual or the Haynes book.

Well I can't tell you anything about the system but I had my W124 regassed in September. I tend to be a cautious fellow so although I didn't have any problems I reckoned it was best to regularly maintain the air con in the same way that you should replace radiator coolant and brake fluid (prevention is better than cure). Anyway the equally excellent Andy Gale charged round about £60 (sorry can't find the bill for exact price). So it looks like anywhere between £50 and a £100 is about right. My system is an after market Davia fitted approx 6 years ago by the previous owner (don't think it'd ever been re-gassed until I had it done)

And to the techy guys is R2D2 also a refrigerant

 

[boblez]

Thank you all for such a detailed answer to my question. I too have learnt more from this thread than any Haynes manual could have taught me.

I recently got hold of Mercedes Service Manuals on Disc (dont ask too many questions!) Comes with diagrams etc but they didnt give me as much information as i have from this thread.

So, once again i thank you all and i will update when i have found someone to do the regassing till then keep reading

Bob

 

[jeffhosier]

My 250TD air con packed up after about 4 years. The dealer said I needed a new compressor costing about £700. Since I didn't trust the dealer, I had it recharged by an independen (costing about £50 ), and it worked fine for a couple of years. A service by the independent (another £50) got it working again. So I reckon that I can do another 12 recharges before it costs more than a new compressor!

Hope you can fix yours as readily

 

[bapowley]

"Borrowed from the MB Club forum - I have the same problem with my W126 500SEC
I suggest the first thing to check is the duovalve. I'm not familiar with its position in the 124, but I think if you imagine the windscreen and bonnet weren't solid, and the driver reached through them both with his left hand, the first thing he'd touch would be the duovalve. Hope that's not too surreal. Anyway, it has three hoses (2 side by side and one below), and a 3 pin elecrical connector between two small cylindrical things. [I'm sure Derek R will correct me if this is wrong.]

The duovalve should be open (allowing heat) at 0 volts and closed (not allowing heat) at +12V. There are 3 connections to the valve on the 124. Pin 1 (white/green) is for the left, pin 3 (white/blue) is for the right; both connect to the heater controller. Pin 2 (black/pink) is the incoming +12V supply from the fusebox (there may be another wire on this pin, that piggybacks the supply to the coolant pump).

You should be able to test the following conditions with a multimeter, some lengths of wire, some crocodile clips and a matchstick () without removing the valve. The engine should be warm and running, and the blower on.

Unplug the 3 pin connector. Both sides of the heater should be giving hot air.
Check that the voltage between pin 2 on connector and earth is about 12V
Apply +12V to pin 2 on the valve (either direct from fusebox or from pin 2 on connector) and earth pin 1 on the valve to a clean earth point on the body or engine. This should give you cold air through the left-hand vents.
Repeat, but with pin 3 on valve earthed. This should give cold air on the right.

From the symptoms, test 1 seems v. unlikely to fail. If test 2 fails, there is a break in the wiring between fuse 7 (I think) and the valve. If either or both of tests 3 and 4 fails, then you have a duff duovalve. However, from the symptoms, I would expect it either to pass both or fail both, but not pass one and fail the other.

If the duovalve is OK, then we need to delve a bit further.

The other components involved are the heater controller, which is integral with the temp contol wheels in the 124, and three temperature sensors - and wiring, of course. I can't see it being the sensors because setting the temp wheels to minimum is a switching action that is effective whatever the sensors are sensing.

So, if it's not the valve, it seems very likely to be the controller or wiring continuity between controller and valve. Controller pin 6 white/blue goes to valve pin 3. Controller pin 8 (white/green) goes to valve pin 1.

Happy hunting, and keep us posted with findings and results.

PS. When I say 12V, I mean 12V or more.

Did you give the heater matrix time to go cold when you were doing tests 3 & 4? It takes a bit longer to cool down than to warm up, and it cools quicker with the fan on full. Assuming you did, and it it was still always warm, then you can be pretty sure it is a duff valve. The valve should have been forced shut by the application of +12V, so no hot water should have entered the heater matrix and thus the air should have come out cold. None of the other potentially problematic components (controller, temp sensors) were in the equation.

You can check whether the valve is operating at all by repeating tests 3 & 4 with the ingnition off. Make the +12V connection to pin 2 then, when you make and break the earth connection to pin 1 or 3, you should see a spark if there is any current getting through. You can also just about feel the operation by putting your finger on the relevant cylinder on the top of the duovalve unit, and you can hear it very faintly too (just tried this on my W126 to make sure). If it appears to operate, then it is probably stuck slightly open when it should be closed - although I can't see a particular reason why both sides should have decided to stick.

 

[bapowley]

Did the check - all OK - checked fuse 5 and bingo everything now works. The clue was in the fact that the reversing lights didn't work - would you believe they are on the same fuse as all the heater controls - there must be some German logic there but I can't see it.

No matter, problem solved