Photo step by step post showing a W123 evaporator removal (1983 240D and 1982 300TD) - Page 5 - PeachParts Mercedes-Benz Forum

vstech · #61 02-26-2016, 10:48 PM

I'm happy to explain it in more and more detail if you need me to.

but suffice it to say, the system needs both sections working right to properly cool the cabin.

vstech · #62 02-26-2016, 10:50 PM

Quote:

Originally Posted by leathermang

No one is suggesting it is not important for the condensor to be clean... that is the bottleneck of any AC system... air across the condensor...
what I am disputing is this :
"" clean evaporator will cool the cabin better...therefore, it will absorb more heat... the evaporator temp will be higher, the freeze switch will not activate, due to the higher amount of heat intake of the evaporator... that heat will cause more stress on the compressor and condenser."" --Vstech

the ' more stress' implies something bad when we are discussing poor longevity from R4 compressors..... but cleanliness everywhere fins are is less stress on the system designed for clean fins everywhere than leaving the fins of the evaporator dirty...

ahh... I see. all my statements are about EVERYTHING needing to be done...

the above quoted section is fact, and it's about the fact that condenser service is needed as well as evaporator service. place the word DIRTY before the word condenser, and it will make better sense to you.

vstech · #63 02-26-2016, 10:54 PM

Quote:

Originally Posted by leathermang

A clean evaporator does not increase the load on the compressor and condenser.... were you typing too fast when you wrote that? you can correct that and delete this post if you want to...

For the same amount of cold going to the passenger compartment having a clean and thus proper functioning evaporator is the minimum and designed load by the engineers for a given heat load...
any lack of cleanliness or obstructions increases the load and run time of the compressor.

let me try this...

a clean evaporator will impart more load on an ac system than a dirty one will...

better?

of course it won't bring more heat into the system than the system did when new... nobody has a new 123 ac system that I'm aware of on this forum...

lol!

also... there is no "cold" being put into the cabin... HEAT is being taken out of the air and it's returned to the cabin with less heat in it... that heat that is taken out of the air is drawn INTO the ac system. and the heat is pushed into the compressor by the evaporation pressure, and compressed by the compressor, and ejected from the system at the condenser. more evaporator clean surface area, allows more contact with warm air, and more heat enters the lines, and the refrigerant builds more pressure from it.

leathermang · #64 02-27-2016, 12:20 AM

""Concentrating first on the condensor fins needing cleaning and straightening is a low percentage approach on these old cars.... they do need to be clean.... but what gets neglected is the EVaporator fins.... a miserable job to accomplish....and hidden from view so that it gets neglected completely for DECADES.....
The evaporator fins being blocked also works the compressor harder""-leathermang

I objected to the impression given by your use of the word 'stress' ... you have since changed to the word ' load' ...
The idea that cleaning the evaporator fins causes more stress on the system is wrong on several levels.... the LOAD when the evaporator is clean IS the load the system is DESIGNED FOR....
Our compressors basically put out a certain amount of pressure when they are running... the amount of pressure in the system is Controlled by turning the compressor on and off. Our systems are ' cycling compressors' ...
So if you look at a set temperature inside the car (constant heat load )... and you do what is necessary to the blower fan to keep that temperature.....
Then what happens with a factor such as impaired air flow across the evaporator is that the Compressor works longer per unit of time compared to the system fins being clean. Running the compressor relatively longer over the long haul is STRESS.....
So cleaning the evaporator does not cause STRESS....it only allows the compressor to work at its designed load and for the designed percentage of time to produce the desired results..

Tmadia · #65 02-27-2016, 01:02 AM

Vstech is correct. A clean evaporator will add more heat to the system than a dirty one. A clean evaporator will cool the cabin FASTER, but that doesn't necessarily mean more efficiently.

A dirty evaporator will cause the compressor to cycle more, kind of like turning the fan down a little. No big deal, just takes a little longer.

leathermang · #66 02-27-2016, 01:20 AM

Tmadia, You are not addressing what I am talking about...
More heat does not equate to ' STRESS'.... everything working correctly just means the compressor is doing the work it is DESIGNED for ...
Cycling more and longer UNNECESSARILY due to any fins being impaired in their job... when dealing with a compressor with a bad reputation for longevity.. That IS STRESS.

vstech · #67 02-27-2016, 10:14 AM

I'm sorry greg, you are mistaken on several points here.
The compressor builds pressure, but the load on the system will massively affect the compressor.

If you don't start with a clean condenser, cleaning JUST the evaporator will fry the compressor. It will impart more perssure, and heat into the system.

Sure, if the same heat is extracted from a closed system over a long period versus a short period it can stress via excess runtime... but that doesn't happen in a car refrigeration system. Load is constantly incoming. So, a clean evap will put more load on the compressor. More heat, and more pressure. That's stress. With a weak condenser the heat and pressures rise, and equipment fails. Start with a clean and straight condenser. Finish with a clean evaporator and enjoy a well working ac system.

Feel free to ask for clarification on any point here... but it's simple physics and thermodynamics. ..

Quote:

Originally Posted by leathermang

""Concentrating first on the condensor fins needing cleaning and straightening is a low percentage approach on these old cars.... they do need to be clean.... but what gets neglected is the EVaporator fins.... a miserable job to accomplish....and hidden from view so that it gets neglected completely for DECADES.....
The evaporator fins being blocked also works the compressor harder""-leathermang

I objected to the impression given by your use of the word 'stress' ... you have since changed to the word ' load' ...
The idea that cleaning the evaporator fins causes more stress on the system is wrong on several levels.... the LOAD when the evaporator is clean IS the load the system is DESIGNED FOR....
Our compressors basically put out a certain amount of pressure when they are running... the amount of pressure in the system is Controlled by turning the compressor on and off. Our systems are ' cycling compressors' ...
So if you look at a set temperature inside the car (constant heat load )... and you do what is necessary to the blower fan to keep that temperature.....
Then what happens with a factor such as impaired air flow across the evaporator is that the Compressor works longer per unit of time compared to the system fins being clean. Running the compressor relatively longer over the long haul is STRESS.....
So cleaning the evaporator does not cause STRESS....it only allows the compressor to work at its designed load and for the designed percentage of time to produce the desired results..

leathermang · #68 02-27-2016, 11:22 AM

Vstech, In all my posts I have said that the condensor needs to be clean... we have both emphasized that in our AC threads for many years....
The condensor is relatively easy to reach and clean... compared to the evaporator... and we know that evaporators get neglected for decades on a regular basis...
People do all or many or of the other stuff needed for an AC redo... except the evaporator cleaning.....and then are left with the feeling that their system is ill designed or that the R4 is inherently a lacking design. This is exaggerated if they are also changing to the less efficient R134a from the original R12.
Stress is something to be avoided in mechanical systems....Cleaning the fins on the evaporator does not cause stress.... it puts the AC system back closer to when it was new and working correctly. The conditions under which it was designed to work...

Tmadia · #69 02-27-2016, 11:36 AM

So if you turn the fan from low to high is that more stress or lower stress? If you correctly said more stress then you get the point. A dirty evap is no different than a slower fan to the system, it is just absorbing the heat from the interior at a slower rate. That's all vstech is saying.

leathermang · #70 02-27-2016, 11:46 AM

Tmadia, You are using ' load' and ' stress' interchangeably ... which is what I am objecting to.... low or high fan applied to situation does not take the system out of the ' designed parameters' .... but something which developed later due to use.. like clogging the fins on the evaporator introduce Unnecessary wear on the system... defined as ' Stress'....

babymog · #71 02-27-2016, 12:28 PM

Quote:

Originally Posted by vstech

<>it's like mb went... the rich americans need ac to be a luxury car, hey, GM... can you loan us some ac parts? and they stuck in what would fit the grill and made the cabin all fancy and automatic.<>

Kind of true actually.

Back in those days, the Europeans pretty much sucked at three things: Automatic Transmissions, power (windows, seats, sunroof) stuff, and A/C.

None of these were popular in their home markets and they didn't really have much to draw from. A/Ts were sourced from Chrysler and GM, A/C from whomever, power windows and stuff made in Klaus's garage or something. Audi even went to the extend that they tried to solve it by sourcing two key components for their new 5000 from GM: The ACC unit and the power seat bases. Both ironically the highest failure items in that car.

So yeah, the 123 and before had mediocre A/Cs even new, the 201 was a big step forward for M-B in that area as the first design to incorporate A/C from the beginning (and it showed).

vstech · #72 02-27-2016, 12:34 PM

Not budging on this are you...
In automotive air conditioning. .. load never stops unless the cabin is cool... sure in mild weather the temp would satisfy and drop out the compressor or reduce fan speed... but when it's hot and humid, the ac in the 123 or 126 never shuts off, unless the freeze switch is triggered or you stop the car.

cleaning the evaporator will certainly cool the cabin better...

but with r134, and temps in the sun over 96F, high humidity, and stop and go traffic... you better have the best condenser you can get.
If the system satisfies cabin temp, fine... but you have to agree... constant load, clean evap, high pressure and compressor stress...

low load is no problem for a compressor. They will run constantly if pressures stay low... bring up the heat transfer from the evap, and you are going to kill the compressor rapidly
Unless you get the condenser right.

leathermang · #73 02-27-2016, 12:45 PM

Quote:

Originally Posted by vstech

.... bring up the heat transfer from the evap, and you are going to kill the compressor rapidly
Unless you get the condenser right.

No one is saying leave the condenser clogged or unclean.
No one is saying the condenser does not need great air across it.. by fan or forced air by moving forward.

But the idea that CLEANING the hair off the evaporator .... bringing it back to its NEW condition..... will kill it... or be in ANY way detrimental to the AC does not make sense unless you attach the implication that one ( me ) is saying ignore the cleanliness of the condenser ... which I HAVE NEVER SAID....
I said that the condenser is easy to clean relative to the evaporator and people need to address the evaporator cleaning because both finned items in the AC are critical....

Adriel · #74 02-27-2016, 02:59 PM

Greg and John, fantastic y'all have so much time to fill two pages with banter, but, how about a solution?

I ran a R134a, R4, stock condenser, and 70 percent tent windows that hardly look tinted. In 115*F weather, had 55*F vent temperature; y'all can go look for the figure in the prior thread to confirm. So, stock system can do quite well, however, does benefit from a parallel flow condenser, which is now half installed. I am still waiting for vstech to let me know if still selling parts and how much he wants for the fasteners. He is the only source for me, as no classic Mercedes in the yards here.

Humidity does help here, because brings down the temperature (delta t) and moist air transfers heat better. But, difference between 80/80 and 90/90 of the South.

So, do those cleaners in a can really work? Can we inspect the evaporator without having to take everything apart? How about access from the blower hole?

B.T.W., John, intrigued you mentioned dog hair: have experience?

Amazing all the crevices dog hair gets into: have found it behind trim in the DGWGN, from Tram's dog that passed years ago. Left there as a memento.

leathermang · #75 02-27-2016, 03:27 PM

Adriel ,
The bad news is that it is really a pain to clean the evaporator... that is why it is done so seldom...
I think I am the one that mentioned the dog , and other, hair...it does get everywhere..... an iguana lizard will not have that shedding problem.....
There is a great thread by I think Morrison from way back with great pictures...and several good threads on this subject...
What makes it really hard besides the limited access.... is that one does NOT want to push that dust and hair and stuff INTO the fins... so some way of GENTLY vacuuming it upwards ... without bending fins.... is really needed..... then some of the bubbling normal fin cleaners can be used...
ALSO important since you will be needing LOTS OF VOLUME of cleaner and wash flow.... is that the DRAIN in to the outside is working correctly... OR that you have a substitute way to catch that fluid without soaking your carpet ....