W210 Drivers vents warmer than passenger vents
 

99 E300D - Drivers side vents are pumping warm air but the passenger vents are pumping nice cold air. Its been 95 degrees plus in CT lately and driving around with my face over the center console to get that passenger cool air is giving me a sore neck. I also have the hissing noise coming from the vents.


Here are the numbers from the diagnostics. I have the description of these values somewhere but I can't seem to find them. Any help would be greatly appreciated.
1-87
2-102
3-78
4-66
5-85
6-182
7-14
8-138
9-29

On a side note I replaced the radiator a month ago. Hopefully this problem is a coincidence rather than mechanic error.

Thanks,

Mike
99 E300D 199K

The most likely cause is a low refrigerant charge. The cold refrigerant does not seem to make it all the way to the drivers side of the evaporator.

What do you mean by warm air? If you mean ambient or less than cold, then low refrigerant is most likely cause. But it it's actually heated air, then the duovalve is bad.

The hissing is characteristic of a low charge which at #7:14 seems to be your case. My 99 needs between 17-18 to cool effectively, esp. in hot temps. I use a store bought R134 can, but the best route is a professional ac check and refill.

Also your evaporator temp sensor maybe bad. #5 should be = or less than 3 or 4 which are the L/R vent temps. This is an easy 40 min fix and cheap but important part.

Almost certainly low refrigerant.

I decided to add the store bought R-134 to the system. The left vent was pumping cold air instantly and reading 15 at #7. I let the system completely empty the small 12 oz can while keeping an eye on the pressure. It never got past 16 at #7. It took about 15 minutes to empty the can. Both vents are blowing cold, hopefully it stays that way.

Thanks for the help!

Mike

Hate to be a naysayer but chances are this won't permanently fix it.

Had the same symptoms as you, it's the low charge.

If you had a leaky duo valve the #3 and/or #4 (heat core L and R) would be in the mid 100s. Unplug the duo valave, you will get blasted out of the cabin with heat.

#5 in the 80s is another sign. #2 (intake air temp) - #5 (evaporator leaving air temp) is 17 degrees. Delta T should be at least 50 degrees with a properly functioning system.

My compressor ended up seizing from operating too long in sub optimal condition. The proper fix is about $1000 and about 4 days of your time.


http://www.peachparts.com/shopforum/diesel-discussion/377507-w210-compressor-seized.html

When I had the same symptoms on my 98, I added refrigerant and it's been perfect for over two years. So far so good.

Only ten more months until my son assumes complete financial responsibility for the 98...so just need to make it until next June! ;)

AC is still working fine.
I also noticed when the AC compressor turns on, the engine RPM doesn't drop as much, the engine is much smoother when the compressor turns on then before adding 12 oz refrigerant.

Here are the new numbers.

1-69
2-112
3-44
4-44
5-39
6-188
7-16
8-141
9-32

Ambient 76

What do all the values represent? I have this list somewhere but I can't find it.

Looks like the original chart has disappeared from its source, but it is hosted at mbworld forum http://mbworld.org/forums/attachments/e-class-w210/220695d1319218810-c-question-mb-w210-ac-diagnostics-flap-test.pdf

Here is a quick reference:
1 - cabin temperature (sensor in the overhead control panel by the dome light)
2 - intake air temperature (sensor in the intake plenum) note that this temperature may or may not equal the ambient temperature that is sensed in the bumper and displayed in the instrument cluster. If the car has been parked overnight and the sun is not shining on the car, both numbers are likely equal. But on the road the two sensors see very different environments - the plenum draws hot underhood air and the bumper sensor gets radiation from the road and exhaust from cars in front.
3 - left heat core temperature
4 - right heat core temperature, these sensors are on the face of the heat core
3 and 4 can be used to rule out a leaking duo valve, if 3 and 4 are equal or less than 2, then the duo valve cannot be leaking since the heat core is no warmer than the incoming air. Best to do this on an extended highway drive in the evening in EC mode so the system is at equilibrium and the sun and the a/c don't skew the results.
5 - evaporator leaving air temperature - sensor in the air stream on the drivers side of the evaporator about an inch off the surface of the evaporator (the air flow comes from the passenger side from the blower, across the back of the air box closest to the firewall, goes through the evaporator, then the heat core, and then out the vents).
6 - engine coolant temperature - sensor in the cylinder head
7 - refrigerant high side pressure - in Bar (1 bar = 14.7 psi) - sensed at the receiver dryer
8 - refrigerant high side temperature - sensed at the receiver dryer
9 - unused
10 - blower regulator reference voltage *10 - this goes to the blower regulator and tells the fan how fast to run - 0 to 6 V is stopped to full speed
11 - emissions sensor - located in the intake plenum - a relative measure of hydrocarbon and CO content in the intake air - engages auto recirculate and carbon filter
12 - sun sensor - top of the dash - 4.2 is totally dark 2.0 full sun
20 - aux fan regulator reference signal
21 - engine rpm *100 - I wonder if this is for gas engines only, never seen this number mean anything on my E300, the diesel and gas rpm sensing is totally different
22 - vehicle speed
23 - instrument illumination voltage - 211 is full scale
24 - Vehicle battery voltage less 0.7 V (13.0 V on display is actually 13.7 V bat)
40 - software version
41 - hardware version

Your numbers are looking much better.

I had the same result, it would work great for a couple weeks then start getting crappy again as the evaporator slowly leaked out. I could definitely smell refrigerant and oil in the car after it had been sitting closed up all week (which my car does often at the airport).

After several years of adding charge the compressor finally had enough of this and seized. If the charge does not hold I would not keep charging it, eventually your compressor will die. If you catch it before the compressor dies you can just do an evaporator and receiver dryer replacement. If you wait until the compressor dies (or has been damaged to the point it starts to shed debris into the system) then you will also have to replace the compressor and the condenser. The condenser and evaporator on these cars are parallel flow types that can not be flushed.

One more trick that is not in the document:
push and hold both AUTO buttons for 10 seconds to force the aux fans to full speed. Helpful when charging the system to get the airflow up.

Thanks jay_bob...very good information!

I agree that the problem might not be fixed. I've had my share of AC problems. I changed the evaporator in my 124 several years ago so I know what that is like. I took a look at your recent post & photos, I'm praying I don't have to do that again. Like you said, its not difficult, but very time consuming, and take lots of pictures. Your photos tell the story.

Thanks again,

Mike

The evaporator replacement on a W210 is more forgiving than a W124

Agreed, the 210 dash assembly is much more intuitive and well thought out than a 124.

If you've done a 124 evaporator a 210 will be easy.

So totally worth it...my wife now complains it's too cold in the car.