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Discussion Starter #1
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):

1. Sensors:
Sensor 1 (Inside Temp): 82
Sensor 2 (Outside Temp): 76
Sensor 3 (Left Heater Core Temp): 82 and later 114
Sensor 4 (Right Heater Core Temp): 84 and later 107
Sensor 5 (Evaporator Temp): 80
Sensor 6 (Engine Coolant Temp): 186
Sensor 7 (Refrigerant Pressure): 04
Sensor 8 (Refrigerant Temp): 91

2. DTC Error Codes:
Error B1231 (Engine Coolant Temp. Sensor Malfunction)
Error B1234 (Sun Sensor Malfunction)
Error B1459 (Series Interface (K2) Connection to Instrument Cluster (A1)

3. Additional Data:
10 Blower Control Voltage: 6.0V
11. Emission Sensor: 2.4V
12. Sun Sensor: 4.1V
20. Control Current for Auxiliary Fan: 3.2mA (Is this value too low?)
21. Engine Speed: 44 or 4,400rpm
22. Vehicle Speed: 0 (makes sense to me)
23. Terminal 58d: 32 or 32%
24. Battery Voltage: 13.3V
40. Software Status: 164
41. Hardware Status: 85
42. ???: 40
43. ???: 136

Thanks,
Netdvn
 

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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.
 

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Discussion Starter #3
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?

Cheers!
Net
 

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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.

Good luck.
 

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Discussion Starter #5
wood'sbenz said:
..... 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?

Again, thanks for suggestion.
Netdvn
 

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Discussion Starter #6
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.

Thanks,
Netdvn
 

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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.
 

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Discussion Starter #8
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.

Again, thanks for the help.
Netdvn
 

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Discussion Starter #9
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.
 

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wood'sbenz said:
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.

Thank you, SF E420
 

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netdvn said:
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.
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.

Thank you, SF E420
 

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You can buy R134a at any auto parts store, Wal-Mart, etc...any place with an automotive section will have it. You'll need to buy a can that also has the gauge/hose/fitting attachment too. Fill the AC at the low pressure port. This is located on the driver's side of the engine compartment about midway back and to the outside of the engine. There should be a black dust cap on it and the lines will most likely be aluminum. Remove the dust cap, snap the R134a fitting over it (make sure it is snug), start the car and turn the AC on cold. With car running , release trigger to fill AC system with refrigerant. Watch the gauge, making sure not to overfill if possible. If you're very low, I'd suggest buying a larger can - they usually come in multiple sizes.
 

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Alright fellas, these are great instructions in this thread. I will run out to Walmart and pick up the supplies. Then I will try and perform these steps that you guys provided and report back and let you know the results.

Thanks again! :) -SF E420

Oh btw, is there away to tell how much R134a are in the vheicle's a/c system?
 

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Discussion Starter #15
SF E420 said:
Oh btw, is there away to tell how much R134a are in the vheicle's a/c system?
Buy a can of R134a that has the gauge/hose/fitting attachment. The instruction on the can will tell you how to use the gauge. Make sure shake the can well before and during refilling.

--Netdvn
 

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SF E420 said:
Oh btw, is there away to tell how much R134a are in the vheicle's a/c system?

There is no way to tell the actual volume of refrigerant in the system unless you go to a shop with an evacuation machine that will remove the refrigerant and measure the amount. You can run a diagnostic via your electronic climate control to see how many bars of pressure you have within the system, but with our variable pressure compressors, this will do you little good but to give an initial point of reference after adding additional refrigerant. Once you attach the refrigerant fitting, the gauge will show the pre-compressed pressure in the system. The gauge has color keyed areas for low, normal and high range within the system. The system has a high pressure limit protection feature, so you won't damage the compressor in the extremely unlikely event that you over-pressurize.
 

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thanks a lot wood'sbenz, i thought i was a little low on r134a so i bought some and went to put it in and the gauge registered full, or blue, correct level, so i figured i needed to clean the duovalve, i took it off and cleaned it out and lubed it, but couldn't get it back on without removing the plug, so i tried to remove the plug and broke two of the little copper wires connecting the coils to the plug!! it looks like someone with very small, steady hands and a little electrical knowledge could fix it, but i will probably have to spring for a new one, $175! My own stupid fault!!
 

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Discussion Starter #18
4maticinmedford said:
... broke two of the little copper wires connecting the coils to the plug!! it looks like someone with very small, steady hands and a little electrical knowledge could fix it ...
Opps! Sorry to hear that 4maticinmedford.

Netdvn
 

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a/c problem

i have a 98 turbodiesel with the same problem. i assume that i can fix it the same way that you have but do you think there are any differences between the two a/c systems that may need to be addressed?
 

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How do you get those codes from the A/C. If I understand, you can read then on the A/C control head. What is the secret botton combo to get them to come up?

Thanks,
Frank
 
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