Key components of AC systems on Mercedes Benz W123 W124 W126 W201 

Glad it helped

More to come!

Yeah, AC can be a power hog. Cheers!

Thanks and good luck with your car!

Thx!

Glad you liked it.

Thanks, and good luck. That is a big job. Good luck!

@@straybenzes Thank you. I've heard the expansion valve in particular can be a pain. I've also heard that 201 air conditioners tend to be broken constantly. Do you have any insight as to why that is?

@@DGiTPadre The expansion valve is very well "hidden" behind instrument cluster and steering column brackets. The closeness of the four fittings makes loosening and tightening them quite challenging. You have to have the crows feet type wrenches and you must get the threads started by hand. I have not heard of the condenser of the 201 being more troublesome. In my experience the condenser (much like any other old heat exchanger) gets pretty brittle with age.

@@straybenzes Ahhhh, the expansion valve being a big job, yes I have heard about how difficult it can be to access and replace. Will be fun for sure. Thank you for all that info!

@@DGiTPadre The best of luck to you.

Thank you so much!

If I recall correctly the high temp switch kicks the aux fan into high. The cooling water temp high switch turns off the AC compressor above 105C water temp. I am going over the various issues with the AC next week. All the best with your car!

There should be a relay that turns the auxiliary fan onto it's low setting when the compressor comes on. That relay has probably gone bad.

@@wernerdanler2742 Those relays are probably the sturdiest of the ones installed. The resistor is sometimes the culprit.

@@straybenzes Yes, my Peugeot had a resistor in the line to the fan so I took it out and hooked the wires together. It made the fan run a little faster but it worked great.

@@wernerdanler2742 The concept works the same regardless of brand.

Many thanks!

You bet!

Oh no! That is not only unsafe for you, but when gas leaks out so does the compressor oil. Good luck with isolating the source of the leak. All the best.

Thanks!

That sounds like the system is low on Freon / low pressure. I would check the low pressure port with a refill bottle that does have a gauge. Put the AC on max and see what the compressor inlet pressure is.

The low speed only comes on if the high pressure switch senses a high pressure condition. I would expect for your low speed fan setting not to come on under the conditions you describe. The high fan speed comes on when the S25/5 coolant temp switch hits 105C. Just make sure that the small cubical relays are in working order in the fuse box. I do not necessarily think that you are having an issue with your fan.

Hi Werner. US customary size belts and the rest of the world's belt profiles typically differ in the "V" profile. These should be the European SPZ style once which would be close to our 3VX style. I say close because the angle is off by 2 degrees. Not much and that was most likely not your problem. The difference between the metric and customary unit of measure belt lengths can sometimes be dramatic. The longer the belt, the more tension you need. This was also most likely not your culprit. More likely was that the belt profile was off even more dramatically; as you wrote the belt seated way differently from the original. That was not a good move. Too bad the car is not around anymore, because another likely cause could have been pulley misalignment. We shall never know.

@@straybenzes yes. I am sad I did not keep the car. It did the exact same thing no matter which belt I used. It still puzzles me the belts did not seem to stretch. I forgot I asked about the fuel cooler and you did not say. I realized it would only be on gasoline cars. But I did not think about it much when you mentioned it. I did not think fuel injected engines could suffer from vapor lock. Can they and does Mercedes still use this?

Trying to find spark plugs without resistors is very difficult anymore. I would rather modify plug connectors to non resistor type. On the other hand I have one care where I have used resistor type plugs for at least 40k miles without any problems. Hoping this info will help you make up your mind.

Over the years I have had pretty good luck with no name dryers. Important step is to flush the complete system really well, blowing out the flushing fluid, and then making sure you have the correct amount of the corrcct compressor oil in your compressor and perhaps 1/2 ounce in the dryer before you put vacuum on the system. Good luck.

That would be the two vacuum actuators behind your glove compartment. As of my 1989 you would have to remove the passenger airbag instead. Remove the glove compartment door and the insert. You can either get new rubber diaphragms. You can get them here: www.perfanalysis.com/climate-control/acc-version-ii/ Or you can replace the whole pod, but they are really pricey. Here is what they look like: images.app.goo.gl/HUskZ2GjXR5ZCgWJ7 That link also has good advice on removal etc. This set is among the easier ones to repair. Good luck!

Thank you so much Ralph you’re always a great help stay safe my friend

@@abrahamghannam2137 Same to you and keep your classic car on the road :)

That is most likely due to not having enough Freon gas in the system. Is your mechanic familiar with AC systems?

As I have just bought a w201 and most of the components are similar to youra

I do not mess with the old R12 and convert the systems to R134. The one in the video was converted as well.

How much pressure did you see was present in your system? One test you should do is setting the AC to max and switch AC to ON. Then jumper the pressure switch shown in this video at around 3.30min. If the clutch engages your pressure is still too low for the system to work (find the leak while you are at it). If the clutch does not engage then I would check / replace the Klima relay and double check the AC circuit fuse(s). Finally, it is possible for the climate control unit to have malfunctioned. Good luck!

There is a bit of work ahead of you but you can save a bit of money doing that yourself. There are parts of this job that you are not allowed to do. Venting any Freon into the air is one of them. Get a certified shop to empty your system of the old R12. That can be a chore finding one. Next you will need a full O ring set. R12 O rings are typically black and you will need green ones suitable for R134. That is by far the biggest job to get all O rings changed. The biggest PIA is the expansion valve as that lives under the dash next to the steering column. Flush the system using a safe AC system flush - component by component. You will be glad you did this as years of gunk can make a conversion useless as some components may be plugged / restricted with crud. Next biggie in terms of potential $$$ is the compressor. You will need to change to an ester based oil. If the compressor is more than 5 years old just replace it with a new or refurbished one as those will already be set up with the correct O ring. Also, even slightly worn compressors will hurt your AC cooling performance. Do not forget flushing the evaporator and replacing the dryer. Make sure putting oil into the compressor and dryer. Do not forget to put conversion Schrader connections on high and low system connection ports - the R143 ones are much bigger than R12. Close the system up and put a full vacuum on the system for at least half an hour. I prefer 1 hr. Also leave the system sit for at least `10 minutes to see if there are any leaks. Then fill the system with new Freon. Do not use the gas laced with dye. Most shops do not work on systems that have that stuff in the AC system. The high/ low side pressures are different with the R134 as you need around 10-15% less gas by mass. Final tip: If your system had a lead and the gas is gone - so it the oil. NEVER just top off gas without checking/ topping off the compressor oil. Good luck!

Is the engine idling correctly? Any higher rpm than the 700-800rpm will make the shift to R or even D pretty hard. Also possible is leaky or plugged vacuum line to the gear shift modulator valve mounted to the driver's side of the transmission.

Welding the clutch solid is not a good idea as you will then continuously run the AC which will render any temp control useless and at times overload the AC system. Take the pulley off and that will get you closer access to the electric clutch part. Removing the main fan is also not a good idea as that can overheat the engine and yet, it will also affect the AC condenser performance.

@@straybenzes thanks 🙏 mate I'll do so

@@thulanicele7843 👍

There is no cabin air filter on W126

The low pressure switch on the dryer will prevent the compressor to come on. Also, when you lose Freon gas you also lose compressor oil as well. You need to find the leak first. Do not use leak fixing gas etc. That will only delay the inevitable - you will need to search for and fix the leak.

ok, thank you!

@@artoor4ik777 You are welcome.

Truth be told the aux fan really only makes a sizable difference for the AC condenser not so much the coolant temperature. If your car engine is getting too hot it is most likely not the aux fan. Have you direct wired the fan to see if it actually still works?

@@straybenzes my car is fine from a temp point of view… I was just concerned that if aux fan does not come one to cool ac cooler..I have been led to believe that could damage the ac components…

Are you in the US? Do you have automatic climate control? If so, first run the fan test mode by holding both AUTO buttons down for >10 seconds. My car seems to take about 12 or so. This should set the system for full auxiliary fan demand. If the fan does not run, watch it carefully to see if it twitches every few seconds. If it does this twitching (and you can see it on a connected voltmeter), the problem is very likely a bad motor. If it doesn't do any twitching, yet you can see it on a voltmeter, it is almost certainly a bad motor. If it doesn't do any twitching and you can't see any voltage fluctuations on the wires, it is probably a bad controller. Running a 12V lead to the fan motor is not a valid test; if it runs with 12V, it does NOT mean that the motor is good. This fan control is not a simple relay and ballast resistor.

@@straybenzes unfortunately I have manual ac control only…

@@kubaSWAT Oof. I am unfortunately not familiar with that set up.

Did it lose its charge again?

@@straybenzes after 3 months the acon becoming warm and auxiliary fan not function again. I suspect the pressure switch got problem again

Can you? Sure, nothing is impossible. All it takes is time and money. Would I attempt doing that? No. I would buy one that has AC from the factory. There are too many things that need adapting and by the time you have found an organ donor car and have disassembled your current one you will find so many more parts that need attention and besides of this already being a big job, there will be much scope and budget creep.

The OM603 was not put into the W123. The OM617 never had quite the power the 603 did. The W123 also had non turbo OM617 engines as well as the 2 and 2.4L 4 cylinder Diesel. There are a lot of parts still available for either car. Just watch out, there is more cheap crap offered. When possible go with the OEM parts through the classic center for MB. Finding good used but not abused W123s is getting more and more difficult. There were a lot of folks who messed around with bio Diesel conversions. I would stay away from those - most were unfortunately done unprofessionally.

It all depends on your budget, time, and efforts (if you can do it yourself). If you have to contract this out to someone I would say this is definitely not worth it. Personally, I would either live with no AC or look for a good car with AC in it. There are so many systems that need to be messed with and the really involved part is tearing out the heater box/center console in order to be able to install the evaporator. It will not increase the value of the car as everyone stateside expects AC as a basic accessory. If you really love the car I will be the last person stopping you from doing the conversion.

@@straybenzes Thank you very much!

@@DS49er1 All the best.

Certainly. Go ahead and drop your questions here.

I am no longer messing around with R12. Too nasty and expensive. I convert my cars to R134. That way regular shops can then also work on the system again. Good luck!

Hmm. Have you tried powering the fans straight from the battery yet? Let's make sure that the fans are actually working.

@@straybenzes Yup, the fans work with direct 12v. I replaced the pre-resistor as the previous one was no good. Also changed the temp switch on the head, also checked and changed the relays. The fuses are all good as well with new ones.

@@arnog9959 Hmm. One basic item I did forget to ask. Did you check the red fuse for the fans in the fuse box? I have found plastic ones melted and ceramic ones corrode to the point that they looked ok when in fact they no longer made a solid electrical contact.

@@straybenzes Hm, I replaced all the fuses that were marked for fans, and anything else that looked words with new fuses. Im very puzzled, by the aux fans, no lo or high settings even when jumping the temp sensor or the at the dryer. I might give in and take it to a shop...Or Hotwire the fans to relays and a manual switch..

@@arnog9959 Do the relays change state? That would be a good indicator if it may be the climate control unit. That is what I would do next. Good luck.

The older the car the more difficult it is finding good mechanics. Hopefully your car was fixable.

The high and low access ports now have adapters as the R12 and 124 Freon connections are not the same.

Were you able to fix that?

Thanks and I am glad you liked it.

I stand corrected. This is indeed the S32 high pressure AC switch, but it actually is open at 15Bar and closes at 20Bar on US spec W126.

@@straybenzes green switch is 20bar on 15bar off.

@@altezzabmw I am going by factory spec not the color. Where do you get this info from?

@@straybenzes www.w124performance.com/service/w124CD1/Program/Climate/83-544.pdf

@@altezzabmw Thank you! That was not included in the W126 documentation. It is great that the W124 information did mention the switch settings. Be safe and stay healthy.