The A/C on my MB E320 (Year 2000) is no longer blowing the cold air (set the A/C to LOW). I ran a diagnostic and collected the data but I have no clue if those numbers are indicating a good or bad news (particular Sensor 5, 7, 8 …). Where can I locate the defected sensors and what should I take a look first to correct the DTC error codes?
Followings are raw data I collected from the tests (EC was OFF while running the diagnostics):
I had a similar problem which made my car run really hot.
The air come'n out of the vent was really hot.
The dash would even get pretty hot.
I took it 2 my main man & he said it just needed a refill & a new solenoid(I think).
(Was quite a while ago don't remember all to well. Don't quote me on the solenoid part)
I'll go thru my records 2 see what I needed 2 get replaced.
Thanks GhostDogg, Sensor 7 shows refrigerant pressure is 4 and I think it's too low. I bought a bottle of R-134a and have not recharged it yet since I don't know what is the correct pressure. Does anyone know the correct range for Sensor 7?
You're low on R134a refrigerant. At this point your compressor isn't even engaging. With the car running and AC on, add one can of refrigerant at the low pressure port and you should be OK. We have variable compressors, so the refrigerant pressure will vary with the ambient conditions and the cabin temp. On a hot 95F day with a hot interior cabin, the pressure will be much higher than on a mild 75F day. If you still have warm air after refilling the system, then you most likely need to clean / lubricate the duovalve which is about a 5 minute chore.
..... If you still have warm air after refilling the system, then you most likely need to clean / lubricate the duovalve which is about a 5 minute chore.
Good luck.
Thanks Wood'sbenz for the information. I will recharge the system today and hope the problem will go away. BTW, in case I need to do it, where is the duovalve and how to clean it?
Added one can of R134a and got a very very very little improvement. It still blows the warm air but not warm as before. Cleanning the duovalve is my next step but don't know how to.
Duovalve is located on passenger's side in the engine compartment, just forward of the fusebox. It is easy to spot as it has two small cylindrical aluminum cylinders. There are 5 torx (I think t-10) screws holding it together. With the car COLD, remove these torx screw (use a magnetic drive so as not to lose a screw). Leave the electrical connection alone. Once the screws are removed, gently remove the aluminum cap of the duovalve - pulling straight up - you may need to use a thin/flexible putty knife to GENTLY loosen it at first. You'll see two plungers in the lower portion of the valve. These are probably sticking open on you, allowing hot coolant to flow through your heater core, negating your AC's cooling capacity. Gently remove the plungers, dry and clean them with a clean rag - you can use carb cleaner if they're really funky. Once cleaned, lubricate the lower portion of the plungers with some vaseline and put everything back together.
FYI - I needed one and a half cans to recharge my AC. If you hear a hissing sound from your center vent with the AC on - you need more refrigerant. My car was a Florida vehicle and hadn't been driven much in the last three years. With fresh refrigerant and a clean duovalve all is perfect now.
Last edited by wood'sbenz : 06-08-2006 at 04:12 PM.
Great instructions and very helpful hint on the magnetic drive (it is impossible to retrieve the screws if they drop into the cavity between the firewall and the controller box). I cleaned the duovalve this evening and will have a long test drive to DC this weekend.
As of today, the AC seems working OK after cleaning the duovalve and adding 16 oz of R134a. Thanks to Wood’sbenz. Following are the pictures I captured while working on the duovalve cleaning job. I strong recommend to use a rag or paper towel to block the cavities around the duovalve so screw or other parts don't drop into it. Trust me, you don’t want to drop anything in there.
Duovalve is located on passenger's side in the engine compartment, just forward of the fusebox. It is easy to spot as it has two small cylindrical aluminum cylinders. There are 5 torx (I think t-10) screws holding it together. With the car COLD, remove these torx screw (use a magnetic drive so as not to lose a screw). Leave the electrical connection alone. Once the screws are removed, gently remove the aluminum cap of the duovalve - pulling straight up - you may need to use a thin/flexible putty knife to GENTLY loosen it at first. You'll see two plungers in the lower portion of the valve. These are probably sticking open on you, allowing hot coolant to flow through your heater core, negating your AC's cooling capacity. Gently remove the plungers, dry and clean them with a clean rag - you can use carb cleaner if they're really funky. Once cleaned, lubricate the lower portion of the plungers with some vaseline and put everything back together.
FYI - I needed one and a half cans to recharge my AC. If you hear a hissing sound from your center vent with the AC on - you need more refrigerant. My car was a Florida vehicle and hadn't been driven much in the last three years. With fresh refrigerant and a clean duovalve all is perfect now.
Thank you Wood'sbenz for the detail steps on cleaning the duovalve and thank you netdvn for posting excellent pictures. I have an E420 1997 and I am experiencing the same problem with my air conditioner too. However, when I turn on my a/c it works for a few minutes and then starts to blow warm air, not hot air. I don't have a computer so I can't retrieve the codes to share with you fellas. I do want to try and fix this myself because I have donated too much money already for other unexpected repairs. I need your help with the following questions before I proceed:
1. Where can I buy some R134a refrigerant?
2. Please provide detail instructions on how to fill the a/c system with refridgerant.
3. Any other suggestions would be greatly appreciated.
AC Quits Blowing Cold Air 
Linear Mode
