Onericali

Hi,

I've got a 2002 c230.

My AC won't blow cold. The heater works fine, although, it seems to take a while for it to get hot.

I recently replaced the climate control unit, because the knobw as cracked.

I went to Greffs motors, which has a master Mercedes mechanic, and he said:

The compressor is bad.

And that it also isn't getting power from the front left SAM.

Now, I need to know everything about this so I can try to DIY it, but, I'll start with just a couple basic questions.

If the SAM isn't sending the AC power, how do we know its bad?

If, when manually touching the AC with our own power, and the fan turns on ( I had another mechanic do this), how could they know that the condenser is bad?

So, what further diagnostics do I first need to do.

I'd like to determine whether it is condenser related, SAM related , or sensor related.

Thanks

Glyn M Ruck

Point one. Is the system correctly charged with refrigerant? There is a compressor protection circuit that will not power up the compressor if the system is not fully pressurised. (pressure/temp sensor)

System requires proper pressurisation before you can check anything. And requires to maintain that pressure (no leaks obviously)

Onericali

Thanks for the response, and I saw in another post you stating this is the first thing that needs checked.

Please let me know how to check refrigerant levels. It seems confusing because, unless I'm using STAR 75-100 bucks, I can only test pressures, which might be correct, or might be false readings of a sensor? Lol...

For starters, though, does R12 come with a guage?

Should I get a rudimentary diagnostic kit? If so, what would you recommend?


Here is a way also that I came across:

1. Locate the receiver/drier. It will generally be up front near the condenser. It is shaped like a small fire extinguisher and will always have two lines connected to it. One line goes to the expansion valve and the other goes to the condenser.
2. With the engine and the air conditioner running, hold a line in each hand and gauge their relative temperatures. If they are the same approximate temperatures, the system is correctly charged.
3. If the line from the expansion valve to the receiver/drier is a lot colder than the line from the receiver/drier to the condenser, then the system is overcharged. It should be noted that this is an extremely rare condition.
4. If the line that leads from the receiver/drier to the condenser is a lot colder than the other line, the system is undercharged.
5. If the system is undercharged or overcharged, have it checked by a professional air conditioning mechanic.

However, this probably relates to people that's AC gets somewhat cold at times?
Go Saints btw

Onericali

I can't get the low pressure manifold guage to snap into the low pressure valve. I tried with the car off, or with the car on and ac running. I also pressed the low valve down to see if it would blow out any pressure and it did. Could there just be something wrong with the coupler that connects the manifold guage to the low pressure valve, or is there some special technique?

I found this info somewhere in response to the question of what the low valve pressure should be on : "Model: 203.040 Engine: 271.948

"I don't have the official specs handy - they depend upon temperature and humidity and are usually a graph curve - but anything less than 25 at idle and maybe 15 at 2000 RPM is too low.
Here are some standard techniques for A/C charge diagnosis:
With the entire system at ambient temperature, a rough indicator of state of charge is the pressure. It is roughly ambient temperature in PSI, but a manifold gauge set has a more accurate calibration scale for pressure versus temperature. This will tell you if the charge is even close or not, but it is not perfectly accurate.
With the system on MAX (in an MB, engage defrost) for 5 minutes, check both high and low side.
High high and low low side means a clogged evaporator (or line to/from)
Low high and high low side means a weak compressor
Low high and Low low side means low charge
High high and high low means overcharge
High should be around 250-300, low 30-40.
At 2000 RPM, high gets higher and low gets lower.
A decent-enough manifold gauge set is available at Harbor Freight for under $40."

Onericali

The low valve connection is 3/8, non threaded quick disconnect.