Back in 2022, I fitted an upgraded A/C condenser to my 560SEC.   The A/C in that car wasn’t too bad, but the parallel flow condenser made all the difference.  From what I read, this is car more effective when using R134A.

The company that supplied the W126 condenser, Klima Design Works, have just released the 107 version.   This presented an opportunity to finally give the 450SLC the A/C that it deserves.  The kit comes with the upgraded condenser, plus the brackets and lines that you need.   You need to supply your own drier.

I supplied the kit to my mechanic to do the work.   From what I gather it was a bit more involved than the W126 install, probably because space is tighter on the 107.   During the install we found a hard line was missing.  While the line was possibly lost during customs inspection, Klima sent me another at no charge with very fast shipping, which I appreciated.   The kit bolted together well, the only slight issue we had was an existing A/C hose was a tiny bit short, and we had it remade.  Not sure if this was a RHD thing.

In any case, the difference is really noticeable.   While it wasn’t a very hot day when I picked the car up, I was quickly able to make the cabin too cold.   Even on not particularly hot days I was never able to do that.   I’m looking forward to trying it out on a really hot day.    So far I really like this upgrade.

While the new condenser is unpainted and the old one is black, once the bonnet is closed you could hardly tell.   I don’t want to paint it as it would probably loose some efficiency.  It is probably not an upgrade for a show car.  For a car like mine with 315,000km on the clock and used regularly, it is great.

While the car was in the workshop, it had all the bushes in the control arms replaced, and the front brakes done.  Some of the control arm bushes looked pretty bad, and the brake rotors had quite a lip on them.

I’m about to take the 450SLC on a 3,700km road trip.  This 450SLC A/C upgrade should really make a difference to how the car goes on that trip.   I’m also in the process of having the upgraded W126 condenser put on the 560SEL.

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The Mercedes-Benz club have started running mid-week pop-up drives.  I’m not normally able to attend mid-week events but I have a bit of time at the moment.   This weeks drive was down to Berry via the Royal national park then back via Macquarie Pass.

In order to keep up with the other cars on the twisting roads and steep inclines required a lot of use of the higher rev ranges of the M129.    The car certainly seems to be running better after this extended test drive.    We had four cars on the drive, a R107 380SL 5.0, a BMW 545i and a C250.

While the car is running much better now, I did have a couple of other issues to contend with.

The first was strange behavior from the radio.   It stopped responding to inputs of the buttons, and event more strangely continued to play even after I had shut the car off and removed the key.   This is quite odd as the radio has two power inputs.   A constant 12v and a switched 12v.   It is not supposed to work without the switched 12v.

Disconnecting the battery obviously caused the radio to power down.   Even after a 20 minute coffee break which I thought might reset things, it was still operating strangely.    It powered back up but was still not responding to button inputs.  I could not turn it on, and it remained in standby even after I turned off the car.    As you can see from the photo, the key is out but the radio remained on.

I also had a problem where my A/C was not blowing especially cold and would sometimes stop cooling at all.   If I turned it off for a while and turned it back on again, I would get some cold, but it wasn’t that cold.    I don’t think it is low freon because it would be cold for a little while and the compressor clutch remained engaged even when it wasn’t cold.

At one point I was thinking maybe it was an ignition switch problem?   However, I was soon able to eliminate that.   I removed the radio from the car and tested the two 12v inputs with a multi-meter.   The switched voltage was behaving exactly as it should.  Even more oddly, once I plugged the radio back in in, it behaved normally.   I’m not really why it would reset when removed when it didn’t from a disconnected battery.

With the ignition switch ruled out, and the radio working again, it was back to the drawing board for the A/C.   I will need to have the car checked, a set of gauges should be able to check if the freon level is sufficient.  It may also show up something like a bad expansion valve.

Still, the MBCNSW Pop up drive proved to be a good day out and a great extended test drive for the 250SE.

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The W126 Klima relay is more of a control unit than a simple relay.   It has multiple inputs that determine if the A/C compressor should not engage.   These include:

• During full throttle
• When the engine is very hot
• Invalid compressor speed (e.g slipping belt)
• Not enough coolant in the system

This additional functionality makes these relays more sensitive than the little silver ones used in the previous car.   I also had to change the same relay in my 560SEC.    It is important to note that the V8 relay is different to the one used in the Inline six.

The relay is located next to the fuel pump relay near the fuse box.  It is a simple swap out.

I bought a KAE relay.   I had previously replaced the relay with a rebuilt unit about two and a half years ago.   As it has already failed, I went with a new one.   The KAE unit is made in Germany so I hope it lasts longer than the rebuilt unit I went with.

With the new relay, the A/C is now cool again in the 300SE.    I may gut the innards of the broken relay so I have an easier way of jumping the ports for troubleshooting if/when I need to.

The post W126 Klima Relay appeared first on Classic Jalopy.

I took the car in for the gas pressures to be checked and the gas was not below minimum spec.   A tiny bit was added but my mechanic told me he thought it was probably an electrical problem.

Mercedes-Benz USA published a very good Service Manual for the Automatic Climate Control in the W126.    There are often copies on USA eBay and some bad scans are available too.     The relevant section is Testing compressor protective cutout, in the addendum for the 1986-1991 models.    This manual is pretty much a must have if you want to work on your W126 A/C.

There is a step by step test procedure I used to isolate the problem.

1. Test low pressure switch on receiver/drier.   Test OK
2. Testing supply voltage to the control unit (Klima relay).     Test OK.
3. Testing control voltage for A/C compressor from low pressure switch.   Test OK.
4. Bypass relay by bridging pins 5 and 7 and check that compressor cuts in.   Test OK.
5. Test RPM sensor for A/C compressor.    The required value is above 0.3V~  My reading jumped around a bit but was nearly always above that reading.
6. Test RPM signal (TD).   Test OK.

There is a separate troubleshooting guide for the diesel engines that is different.  It is easy to use the wrong one as the labels are on prior pages.

Based on these tests, it looks like I require a new Klima relay for my W126 A/C.   This is rather annoying as I replaced the relay back in December of 2017.   At the time I purchased a rebuilt unit as I figured I would get a rebuilt factory one instead of an aftermarket unit.  I ordered a rebuilt aftermarket unit, so this time I have gone with a new aftermarket unit.

I had hoped to swap the relay with the 560SEC, but the relays are different from the straight six to the V8.

Right now I am driving around with the relay bypassed.   It is rainy and humid and I need the defrost capability, it not the cooling.

The post W126 A/C no longer cooling appeared first on Classic Jalopy.

I went through the entire climate control system of the car as part of my troubleshooting.   I found that the car had a missing aspirator fan, a very noisy blower motor, and an intermittent climate control unit.   These were all changed.   The next step was to take the car to my mechanic to fit the new compressor and receiver/drier.  During the disassembly he noticed that the large A/C hose was slightly weeping.  Changing this hose means removing the compressor, so now was the time to do it.   Of course, it is not your regular A/C hose.  It also functions as a way of cooling the petrol going into the fuel distributor.

The hose was sent off to be repaired, as purchasing this hose new from Mercedes-Benz would probably require giving up your first born child.  This involved leveraging the fittings with new A/C hose.    Interestingly enough, while the hose was being rebuilt, I was driving the car around without this cooling function and didn’t notice any adverse effects.

Sourcing the A/C compressor was not as simple as you might think.   The electronic parts catalog calls for part number A0002302411 for cars equipped with self-leveling rear suspension.  As an Australian delivered car, mine is so equipped.   This translates to a Denso 10P15C.    Cars without self-leveling rear suspension require A0002301111 which is a Denso 10PA17C.  These compressors do not look alike, to the point where it looks unlikely that the wrong compressor would fit without modification.   The 10PA17C is cheaper than the 10P15C.

Today, the new compressor was fitted, along with the new receiver/drier and the car gassed up and ready to go.   When the compressor clutch went out, it shorted out the Klima relay, so this is the final thing that must be replaced.   The A/C does work when the relay is jumped.

At the same time, I had been smelling petrol when starting the car.  Turns out the fuel pressure regulator was faulty and was squirting extra fuel on startup.   Apparently to stop petrol leaking out, this goes into the intake.   Changing the regulator is likely to improve the fuel economy of the car.

This has been a rather expensive exercise, but so long as I am not hit by an inattentive SUV driver, I should have a reliable W126 daily driver for the long term.   Some of the most likely potential problems have now been sorted out.  This includes rebuilding the climate control, new water pump, head gasket etc.

The post W126 A/C almost blowing cold appeared first on Classic Jalopy.

This fan is located behind the glove box, so I removed the glove box and the kick panel below it.  However, to my surprise the fan was missing!  The connector for it was there, but no aspirator fan.   Since I have already bought a new one, I will try and re-fit it.    Even though the noise I was getting did not vary with the blower speed, it appears it is from the blower.   Since the blower is on another fuse, I will worry about it later.

The next thing I did was replace the missing relay that is for the Aux fan.   I am not even sure how relevant this is as the Aux fan wiring has been messed with at some point.  Relays are cheap and so I replaced it anyway.

The car is now looking rather stripped down, with no radio, missing console panels, glove box, kick panel etc.  It will probably be like this for a while as I am not any closer to solving the problem.   At least my car will have an aspirator fan.

The post Further 300SE A/C Troubleshooting appeared first on Classic Jalopy.

The first thing I tried was changing the Climate Control Unit.  This is the push button unit in the dash and they are known to cause erratic climate control if they start to fail.   I was able to purchase a used (but untested) unit for $25.

This change did not seem to make any difference.  I noticed that the compressor was never engaging even when on max cool.  Therefore, the next thing I tried was removing the Klima relay and bridging pins 5 and 7.   The Klima relay controls the A/C compressor and determines when it should engage.   It uses various sensors to control the engagement of the compressor as well as the cooling fans.    This eliminates any of the sensors.    Bridging these pins should bypass all these sensors and simply apply 12v to the compressor clutch.

Doing this and starting the car did result in the compressor engaging briefly.   I even got a bit of cold out of the system!   However a few minutes later fuse 5 blew and the Climate Control System shut down.      Fuse 5 controls most of the climate control functions (except the blower motor), so the next logical step seemed to try and eliminate what could be causing it to blow.   Next thing I tried was to disconnect the mono valve and the Aux water pump.

The Aux water pump is a small pump that increases the flow of hot coolant through the heater.   These pumps are known to draw too much current as they age and are really not necessary in warm climates.    At -20C, having the extra pump does ensure hot coolant from the engine reaches the heater faster.   The mono-valve is used by the climate control system to control how much coolant comes into the system.   (i.e. none for max cool and full flow for max heat).

Fuse 5 still blew, despite eliminating the aux pump and mono valve.   This time, It happened even before I turned on the engine.   Next step may be to test the compressor clutch with an external power source.   This would eliminate some problem with the car’s wiring.

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