fju2112

we've had 74 and 84 degree days in the past few days here in boston. i tried using my a/c the first warm day (friday evening) when it was in the high 60's and turned the A/C down to "lo". It wasn't cold from the two front vents on the driver's side. It was kind of cold on the two passenger side vents, strangely enough; I made sure "EC" was off and that "Auto" was on, and that both dials were down to "lo".

Then it was 74 the next day. Same thing except this time the driver's side was a little bit cooler, nearly acceptable; the passenger side was still colder though. Then yesterday, it was 84. After work I get in my car and crank the A/C...I can still feel that the passenger vents are blowing colder air at the same setting than the driver's side.

I'm searching the forums to see if anyone else has experienced this. Could this be an internal thermostat issue? I can't imagine if one side is working fine and the other is not that I need to juice up the system w/ more freon or have the compressor fixed, but who knows. I have an appt scheduled for thursday w/ my mechanic. Any suggestions in case anyone knows what's going on would help relieve the anxiety!

Frank

lexrex

Get a recharge. Archives will explain.

raymond g-

read this first....
http://www.eclassbenz.com/node/27


...then, run the following diagnostics
http://www.eclassbenz.com/acdiag

zx11blade

Mine is doing the same thing. I am going to the auto parts store to get a A/C pressure guage and some Freon. I haven't charged the system in 2 years.

Benzs

I had the same problem and I put in a 12oz can of R134A
Has been working fine.
It is normal to loose about 10% of refrigerant per year.

1benzguy

You can chase you tail on this one. You need to run the secret menu test,, read the error codes, and run a flap test.
These three test are very easy, and will tell you in detail exactly what is going on.
Don't just slap in some freon and risk very bad damage to the system.
BTW all should run these tests to keep your system in good shape!

BG

1benzguy

OBTW does anone have a list of 'correct' ac code?
like #7, a proper, or range of proper pressure levels?

THX
BG

1benzguy

Thanks for the help forum
Recharged and it works great.
#7 should be 14-15 under load.

sosh

This is NOT normal. If yours is doing this you have a leak that should be addressed

Lancelot

Yes it is normal and what every A/C shop and car manufacturer will tell you. Just the constant compression and decompression of the refrigerant alone is causing this. It has nothing to do with a leak...

Benzs

Agreed

sosh

You have been given some inaccurate information. Think about the laws of physics and your high school physics class. The only way the gas can decrease in volume or pressure is to have a leak in what should be a closed system. Its possible that you have been told this as an excuse for not finding a minor leak but in my book 10% a year is not minor. I would find yourself another A/C shop and I would stop believeing everything you are told. If it does not make sense its not true. I have had cars that I kept for over 6 years and the A/C has worked just fine and pressure checked just fine without adding any gas. With your threory I would have been better than half empty with an inop system.

fju2112

exactly sosh...my mechanic told me there is a leak in the system, and to locate it they pumped more freon into the system and some stopleak chemical dye which will allow them to pinpoint the leak in a couple weeks. i'll keep everyone updated.

sosh

Hope you were mistaken that the guy put stop leak in the system. That can do more damage than you already have. Perhaps he just used a dye to spot it and thats fine. There are also handheld electronic sensors that can sense and pinpoint a leak. Did he try to use one of those?? Common places for leaks are compressor seals, fittings and the condensor. Good luck. Some are difficult to spot and don't give any creedence to anyone that says its normal. Adding gas without fixing it is the cheap half assed way out.

fju2112

sorry - they didn't put stop leak in; it was my bad on the wording. they put the dye in so they could find the leak and ultimately "stop" it once they can pinpoint it

this shop has a very talented group of guys working there and are very professional (the owner specialized in Alfa Romeo, then branched out to all foreign cars; his shop is right next to the old Alfa dealership in Waltham, MA), so i trust whatever he did or tried didn't cut it and they had to use the dye.

they added freon in to both give me A/C for now, and also to help track the leak as there wasn't much left in there to begin with.

Rich H

I own a 2002 E320 and I found this thread very useful as I have had a similar issue with the A/C not blowing cold air at time.Thank you for all your comments on the issue. I did run the on-board diagnostics and ran the codes thru the online program tool. although, the faulty evaporator temperature sensor 'b' code didn't come up, the explaination given by the tool indicates that the evaporator temperature sensor is bad since the reading on #5 was 107, 103, 107, 106. (I ran the diagnostics a few times on different days).

My question is, is there a normal evaporator temperature ? is it 32 degrees F ? I know there are probably some other factors that might be involved but on an average does ayone know what might be a normal reading range? thanks much.

bicylindrico

It is likely the Rec/Dryer. I know it sounds weird, impossible, crazy, etc. I ran into this in the past on a 210 and never saw the problem on a car ever again. Trust me.

Rich H

The Rec/Dryer? pardon my ignorance but what is that?

bicylindrico

The receiver/dryer is a round container located on the high side of the system and is used as a desiccant to remove moisture from the freon. It will be located behind the left headlamp assembly. I believe the problem was with the rec/dryer partially plugging and acting like a second expansion valve. There was an MB bulletin on this years back and the replacement fixed my problem car. They should be replaced anytime the system has been empty or opened up for repairs.

bicylindrico

Bologna! The people telling you this are people that are either lazy, ignorant or lying. If I didn't want to spend the time tracking down a very small pain in the **** leak then I would have told you the same.

lexrex

Rich,

How hot was it outside when you ran the test? It's impossible for the evap temp to be more than a couple degrees warmer than ambient outside air. If it's 80 degrees out and you're getting 100 degree evap readings, your evap sensor is bad.

A plugged up receiver-drier or evaporator expansion valve could block refrigerant from getting to the evaporator. The effect would mimic a low charge problem EXCEPT that your refrigerant pressure value (#7) would be much higher than expected because the compressor would be pumping against a blockage.

You may have additional problems beyond the evap temp sensor. But you really can't determine anything until you have a functional evap temp sensor.

To answer your question, a "normal" evap temp reading on a working A/C reaches somewhere between about 33 and 42 degrees. What you really want from the sensor, though, is an accurate reading. As I explained above, you know you have an inaccurate reading when it's reading well above outside air temp.

Rich H

Thank you for your response. in the 4 different days I did the test, the outside temps were 57, 75, 66 and 80.. the #5 sensor was reading ovr 100 on each day.. The #7 pressure read 06, 14, 08 and 08


I think my mind is made up. I will look into replacing this sensor and then take it from there.. I think my extended warranty will cover it.. if not, i'm still going to have it fixed.

Rich H

One more question just out of curiosity. if the sensor isn't changed or this has been going on for sometime unnoticed. is there any damage that can occur that might creep up later perhaps on the compressor etcc?

lexrex

Short answer: Yes, a bad evaporator temp sensor could lead to damage of your compressor, evaporator and/or blower motor. This damage occurs as a result of the evaporator freezing. Anti-freeze protection is critical, so the A/C system disables the compressor if it detects the temperature sensor is faulty. Unfortunately, the system doesn't always know when the sensor goes bad.

Long answer: The evaporator works like a radiator in reverse. Warm air passes through the evaporator, transferring heat from the air to the cold refrigerant inside the evaporator. Refrigerant enters one side of the evaporator cold and exits the other side hot, carrying heat from the air. The whole purpose of the A/C system is to keep the evaporator cold so that this heat transfer can take place.

The A/C system monitors information from the evaporator temp sensor to ensure that the evaporator doesn't drop below the freezing (32 degrees). If the temp drops below freezing, the moisture in the air eventually ices up the evaporator.

An iced up evaporator can cause damage to the climate control system in several ways.

Airflow slows way down once the evaporator ices up. The resistance to airflow puts strain on your blower motor, which can damage the motor or its regulator.

Water expands as it forms ice. This expansion forces apart joints in the evaporator, causing leaks. This is, I think, the greatest concern.

Finally, a frozen evaporator causes the low-side pressure to drop, which intensifies the pressure difference between the high-side and low-side. This strains the compressor.

Rich H

lexrex - thanks for the explaination. I'll post how I made out..