Onericali

I want to eventually compile a mega DIY for AC, going over absolutely every basis for the C230. I've been researching for a year, mainly because I was quoted over 2000 dollars from the Indy Mercedes shop, and any time I talk to a regular Indy shop, and I tell them exactly what I need done (but havent yet done myself because I tend to be slow about putting things back together), they tell me what they are going to do, which is usually exactly what I started off telling them I didn't need done.

That being said, this is my attempt to compile my knowledge, and really come up with a game plan for attacking this on my own. So, in essence, this will be one kick *** DIY eventually, with links to other DIY's for each portion.

Don't sticky it yet though if you plan on it, because there is a **** load more that needs added, and I don't believe I can edit my post after a certain amount of time.

I will get into my particular problem as an example later on, but first I want to start with the basics of AC diagnostics.







The best way to care and repair your AC is to keep a clean system with the proper amount of refrigerant and oil in it, and run it once a month or so. If at any time the AC does not work properly, there are two main categories of problems you need to look up.

Diagnosis Precheck) Apply 1000 RPM for 15 minutes with the AC full blast and check to see if its working. This check is hard to perform in the winter.

Here are the possible causes from most likely or easiest to check to least likely or hardest to check for each of the two categories, A and B.

A) AC not blowing cold at all
-1) Blown Fuse
-2) Blown Relay
-3) Leak-> AC shut off by low refrigerant sensor
-4) Bad Sensor
-5) Clog
-6) Broken compressor
-7) Broken condensor
-8) Fan motor flaps blowing AC in the wrong place
B) AC only slightly cold, or taking a long time to turn cold
-3) Leak – not enough refrigerant
-4) Damaged Sensor
-5) Slight Clog
-6) Weak compressor
-8) Fan motor flaps blowing AC in the wrong place

(This list needs refinement)

One huge difference between many Mercedes' and other car AC's, is that, for example, our C230 has a belt that is connected to the main belt system (be more clear here), that always is turning, as opposed to having a clutch, which only starts the compressor turning when you turn it on. The reason for this is that there is a major power drain when people turn on a clutch, and the no clutch system prevents that. One thing to realize, though, is that just because the compressor is getting supplied with power, doesn't mean it is actually compressing and doing its job. Basically, when we turn our AC on, the compressor moves some valves that begin the compression process. (Be more clear here, add the basic AC faq as well). The significance of this is found with your very first diagnostic check!

0) See if compressor clicks on. In picture XX you can see the compressor, and in the front you can see it turning, but since ours always turns, that doesn't mean it is on. The best way to check to see if it is turning on, is after your car is running, turn on your AC and listen for a click. It actually should be obvious if it turns on.


1) Check for blown Fuse: (Its essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected.) Very cheap part easy to fix.
http://www.ehow.com/how_4898695_use-...test-fuse.html
(Insert cheap voltmeter that works, and also a way to do this without a voltmeter)

2) Check for bad Relay: (acts as a switch which either connects the circuit and sends power to start the compressor compressing, or stop it. The fan and the AC will have different relays, since the fan can run when the AC is not compressing. 10 dollar part often and easy to switch.

(Insert C230 Fuse and relay chart here) (sometimes in manual or side compartment to the right of the glovebox)

3) Possible Leak: There are two types of leaks. Slow, and fast. Either way, when it gets to a certain point, if the sensor is working, the sensor will trip and the compressor will stop turning on.

*The first thing to do is check if the refrigerant level is optimal or low.

You need to hook up guages to your AC system to check the pressure. You have to use the pressure to estimate weight, since it is impossible to actually weigh how much refrigerant is in the system.

I will list the possible ways to find the amount of refrigerant in the system from least reliable to most reliable.

3A1) Buy a can of R134 that comes with a guage. (Sold at Autozone for example). The reason this is the least reliable is that the guage used to check AC pressure, is not only cheap (though it usually is accurate enough), but it only measures 1 of the AC pressures that can help you diagnose.

There are two types of AC pressures to measure, or more specifically, two places to measure it at. One is called the low side, and the other is called the high side. The R134 can guage sold at Auto zone, for example, only measures the low side. The low side guage is usually colored blue.

(Insert low side high side faq description pdf here)

3A2) Buy your own set of guages that have goth a low side and high side (usually red) guage. Just so you know, sometimes they have a yellow nozzle as well, which sometimes works for adding refrigerant. This is a decent option, but the guages at auto zone, or harbor freight that cost 50 or so bucks, aren't the best guages. This is what I have been using though.

3A3) Auto zone will often times let you borrow theirs, or check it for you, for free!

3A4) Indy/ Mercedes Auto

(Insert faq for checking AC pressure here, and chart for what the pressures mean, and also what the pressures should be based on the temperature).

Here is the hidden fact that it took me a long time to figure out.

If the compressor is not turning on, the pressure check is very unreliable. You will notice that as you turn the AC on, the pressure with the fan running will actually cause the pressures to shift slightly, however, that doesn’t mean anything.

If the compressor is off, gradually, the low side pressure will rise and the high side pressure will lower until there is one base even pressure and they are equal. The system has then stabilized.

The tricky thing is that, with low pressure, it actually shows the low side pressure being high!

This is because the low side pressure when the system is off, and has been off for a long time, is very different than the low side pressure of a working system.

3B) If you determine that you are low on refrigerant, either the person before you that put in refrigerant put too little, or you have a leak.

If you have a leak, you have two problems.
1) Low refrigerant and possibly oil
2) A leak, which can make it happen again.

There are two main factors here to consider that can end up costing the most $$$ or time.

3B1) If you simply add refrigerant until the compressor clicks on, you might not have the proper amount of oil in the system, which can ruin the compressor, or if you add some with the refrigerant, and it ends up being too much, can clog it and ruin it! (I do not know the actual likelihood of this happening. When someone’s compressor needs replaced, and they had AC work in the past, this is probably the reason).

3B2) This step isn’t as costly as it is time consuming. If you empty and then refill your system, and don’t find the leak until afterwards, you will have to re empty and then re refill your system!

3C) Proper Leak repair, and refrigerant filling.

3C1) Vacuum out refrigerant. Here is a link of someone doing it, but it is not a Mercedes: http://forums.bimmerforums.com/forum/showthread.php?t=383641 Use this just for a general idea. (Add actual DIY here once you do it).

3C2) Remove Compressor: DIY by rabney72 here: https://mbworld.org/forums/c-class-w203/362993-c-compressor-removal-replacement.html

3C3) Flush System

There are certain parts that get flushed differently, and some that just need replaced. I need help with this part.

Basically, debris can ruin your system, but so can the solvents used to flush the system. I need research on what solvents are actually okay, and pretty much everything for this step.

Here is a basic starter discussing an unrelated AC type:
http://www.aircondition.com/tech/questions/25/

3C4) Use soapy water bubble technique, hopefully find leaks, and replace hoses or valves that are leaking

I need help with this part.

3C5) Add oil in the system before or after you put it back in the engine
http://www.peachparts.com/shopforum/showthread.php?t=131188

The question here is whether to do it straight to the compressor or into the system. It seems that a happy medium is to add some to the compressor, and to manually turn it a few times, but not too much, since it can clog the compressor, and then add the rest to the system, along with the R134.

3C6) Add R134 in the Low side after connecting everything together.

3C7) Add UV dye to make sure you got leaks.

3C8) If leak is detected, try to patch it, but if you can’t, you will have to redo the whole process again.

4A) Check for Sensor. 1 out of the 3 sensors that work with the AC system, trips and prevents the compressor from turning on if the Referigerant (R134) is too low.

There are multiple ways to check this sensor, but none of them either cheap or good.

C320's and other cars (list them here) have digital displays that can give you readings, but for the C230, we aren't that lucky.

4A1) Star Diagnostics (mercedes dealership- I think 65-100 dollars unless on warranty)
4A2) Apply manual voltage to the wire that is between the compressor and the sensor. (Insert W203 HVAC manual with sensor location). The problem with this, is that if the sensor tripped because of low refrigerant, you can damage the compressor by running it. The probability of damaging the compressor, if you only run it for a few seconds to see if it turns on, though, is low, however, it might be better to do other Checks, and prevent the risk.
4A3) Replace sensor, but I'd do the other checks 1-3 first unless you are under warranty.

All I've got so far.
Please help me with the part about flushing, and the soapy water technique to find a leak if the compressor won’t turn on. Like, how do I get to all the hoses, for one. Will the soapy water technique even work? Then I can do it, and finish this DIY. Thanks.