AC Part1: Air Condition Systems 101

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Why you should get in love with thermodynamics

Here comes the 4 part series you all have been waiting for. The ultimate on how to fix the air condition system in your already too hot car. Bored of driving sweating and always going around with the windows open? Now it’s the time, you have been letting this job off for far too long. Brace yourselves, global warming is coming!

I will cover a standard fix of AC system in four parts. Before even beginning you need to know the basics and the theory behind the technology, this will be covered here in part 1. If you are an expert on AC systems then just head over to part 2.

Part 2 will cover how to change the AC compressor. Part 3 covers the changing of the receiver/drier and the last and fourth part covers how you change the expansion valve. These three components are usually the ones you need to care about if your AC system is not working

Automotive AC Theory 

Air conditions are based on the thermodynamic heat pump cycle and if you are really into thermodynamics you can dig into this topic really geeky and deep, but this is not the purpose here. The automotive AC works just pretty much like any refrigerator, this technology is old and proven, no rocket science really. A heat pump moves heat from one source at a lower temperature to another location with a higher temperature with using mechanical work.

Either used for heating or refrigerating the operational principle is the same, but here we are interested in the refrigerating part.

Mechanical work is needed to shift the heat to flow from a colder location to a warmer one since this is opposite to the natural heat cycle in the universe. The mechanical work in a car is made by the car engine.

The vapor-compression cycle is most common for automotive uses. Here it uses a recirculating liquid called a refrigerant that undergoes phase changes to absorb and remove the heat. Many of you have heard about Freon, but this is just a brand name for some types of refrigerant that was common in the olden days, now it is prohibited due to the ozone depletion of such CFC gases. Newer refrigerants do not deplete the ozone layer, but have high global warming potential, so it’s important that you don’t leak these refrigerants out into the atmosphere.

Vapor-compression cycles all have 4 key components: a compressor, a condenser, a thermal expansion valve and an evaporator. For most uses you will also find a fifth component which is the receiver/drier, this is always found in automotive AC.

Schema over AC system
Vapor-Compression system
The compressor

Since the system is closed and recirculating it doesn’t really have a start, but lets start with the refrigerant entering the compressor. The compressor is the part that circulates the refrigerant and is driven by the engine through a tension belt. The refrigerant enters in vapor form at low pressure, but gets compressed by the compressor and it will form a high pressure vapor with higher temperature, known as superheated vapor. It then enters the condenser.

The Condenser

The condenser is a radiator where the superheated vapor runs through tubes where a fan or water cools down the vapor so it condenses into a liquid. Here the refrigerant removes away the heat to the flowing air or water. This is the part where the heat pump can be used as an oven, but in the car refrigeration is wanted and the condenser is just radiating heat into the atmosphere. The colder high pressure liquid is then routed to the receiver/drier as a saturated liquid.

The Receiver/drier

It is located usually before the expansion valve in the high pressure part of the system. They serve three important functions:

  • Temporary storage container for refrigerant when system is not in use.
  • Filtering debris inside system.
  • Removes moisture that can have gotten into the system which can create corrosion and destroy the compressor.

The liquid then goes to the expansion valve where the liquid can drop a lot in temperature.

The Expansion valve (metering device)

The saturated liquid goes through the expansion valve where the pressure suddenly drops, the sudden drop in pressure lowers the temperature of the now liquid and vapor mixture to a much colder temperature than the temperature of the space which need to be refrigerated, like the inside of a car. The cold mixture of refrigerant then is routed to the evaporator.

The Evaporator

Inside the evaporator, which is also like a radiator where tubes crisscross over metal fins to expand the possible area of which heat can be absorbed. A fan blower pushes warm air inside the car through the evaporator where the heat gets absorbed by the cold refrigerant and cold air comes out on the other side. This you will feel as the cold air conditioned air coming out of the vents. The liquid inside the evaporator tubes gets, you guessed it; evaporated into a vapor form due to the heating and carrying this heat back to the compressor completing the cycle.

I hope this was informative and covered the basics, so now you have the understanding of your car’s not so complicated AC system.

Cheers, Robs out 

Why the not so Sporty or Leicht (SL) R129 is the next car you should get

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Why is the R129 SLs so cheap these days and the R107 SL so expensive in comparison? The R107 has already become a true classic since it started production back in 1971. The oldest R129s are already passing 25 years and becoming old. But they are ridiculously cheap compared to what you get. This is a common trait among luxury sedans aged between 20-30 years old before the prices start to go up again, but the SL is supposed to be a sports car and it is a convertible. These types of cars normally have quite higher prices than the aging luxury sedans.

The funny thing is that you can get a V12 SL600 fully equipped for just around 15k Stirling pounds. That’s crazy for a car that nearly cost 100K£ new back in the olden days, especially considering the inflated currency and the value of money back. Why would you even consider buying  new car when you can get this luxury three pointed star of rolling ludicrousness for absolutely less than a single cruise holiday to the Caribbean? Also if you want one R129 in red, they are the most expensive ones, not many came in red and for some reason they are highly valued.

The R129 SLs are also reliable cars where the bigger engines have super strong dual overhead cam axles. Buy it, drive it and don’t bother opening the hood in between services. The only major thing you need to take care of here is the soft top that will deteriorate quicker than the rest of the car. But you probably have a garage right? You can even get them with a hard top which can be used for other seasons than the summer, perfect for northern Europe. Although my personal opinion is that you should avoid driving around in a convertible with the hard top on, what if the sun comes out!?!?

The styling has become timeless yet still feels modern even though it’s a 30 year old design. I have never heard anyone said that the R129 SL looks bad, and in the end that’s what matters right? To drive around in a cool car is first priority. Power, speed, comfort and reliability usually comes second when having a 2-seated mostly unpractical convertible. If you get the R129 you will get all of these except the practicality. Although you will probably fit your unused golf clubs while impressing your business friends that most likely are not good at gold either. (I would rather hang my muddy mountain bike off the back, throw in my diving gear in the boot along with the boots and back pack for hiking, but that’s just me)

So what are you all waiting for? Get out there and buy a cool R129 and drive it!

To be inspired check out these videos about the R129 from Harry’s garage and The Smoking Tire respectively:

Cheers, Robs out 

Ride along in w140 S600 from Japan

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This video I just made for testing camera equipment, camera placement and angles, the noise quality etc. Watch with this in mind and laugh at the ridiculous intro/outro and some weird cutting. Comment on Youtube if you want to give constructive feedback.

I used the GoPro Hero4 and built in mic. Some lessons were definitely learned from this recording session:

  1. The gopro mic is not good enough. Use of external mic and good placement is necessary. Inside car is good for louder cars, but for the S600 the mic has to be placed next to the exhaust.
  2. Shooting inside back of car is difficult when it is very bright outside.
  3. Wind noise needs to be dealt with, external mic inside car or wind muff.
  4. More angles and faster cutting is needed.
  5. Introduction to car and it quirks and voice over is necessary for viewers to enjoy videos. This means I have to pull out my English skils and hopefully not so much the Norwegian accent.
  6. Wide angle shots not necessary for every angle. I have a camera for this purpose too.


Cheers, Robs out 

W140 S600 added to the collection

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Before the summer I acquired a 1996 w140 S600 (Japan spec) as an addition to my old w123 280CE, hence the updated site main picture as of July 2017. It is actually the same car I did the review on last year and the offer was simply too good to refuse. The car is an extremely good find with under 70.000km original km in it’s 20 years lifespan.

The car collection is now larger than 1! My plans with this car is to keep it completely original and use it mainly for long road trips with extreme comfort, silence and unlimited v12 power if you need it. I also hope the value for this flagship will increase significantly since the 600 version is rarer than most production vehicles and the value is now at the lowest it can be.

I will be posting maintenance DIYs where possible with this car, which are extremely rare by the way! And I will be looking into doing car related videos, starting with filming the S600 and then the 280CE. I did some camera tests now in the summer, which I will post almost immediately under the Videos section. I am though planning to making better videos with use of external mic for excellent sound quality which so many car videos lack except high end production.