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1989 300E; 2004 ML350; 2007 E320 4Matic
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Discussion Starter · #1 ·
The Air Conditioning in my 2004 ML350 is not blowing cold air for about 7 months now. I don't drive it all the time so decided to not worry about it earlier but it's again 90 degrees in the Washington DC area this week so I decided to check it out. I read a lot of the Forum threads and advice previously provided by 43sqd and other smart people on this forum and did the following already based on the well researched and reported forum threads Now I would like to know what would be the next best steps to take without actually going to a shop to get it fixed. This is what I already did:

1. Checked the Fuses (F44) and Relay K26 and they are good. I checked the two front fans by giving it the 12V and they are good. I realize that the Fuse 44 and Relay K26 do not affect the operation of the compressor but wanted to rule it out anyway.

2. I checked the white wire at the Coolant Circulant pump and it has 12V at the White Wire with the N22 set to max A/C. With the engine running, I also felt both the low side pipe and high side pipe near the firewall and they were both at ambient temp and not cold or hot.

3. I visually observed the compressor with the engine running and saw that the front shear plate was rotating with the pulley but the center shaft did not appear to be rotating. With the engine off, I tried to rotate the compressor pulley or shear plate by hand clockwise but it does not budge since it is held firmly in place by the serpentine belt.

4. I checked the Static Pressure in the system by attaching my refrigerant gauges to the low and high side. Both sides read zero (0) psi so it indicates that the system is low on refrigerant (or maybe even empty).

Based on the last test, I am thinking it must be a leak and the freon is gone so the compressor won't come on since the refrigerant temp pressure switch must be signalling to N22 that there is not enough freon in the system. Question is should I just try to fill it up with Freon (the small R-134A cans) from the low side port...I am guessing if there is no suction because the compressor is not running the Freon may not even get pulled in from the low side port even if I try....or should I pull a vacuum and see if it holds or somehow do a leak test at home with compressed air or something?

Any suggestions on what to check or do next?
 

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Dallas, Texas
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Get a scanner and read codes then look at actual values in AAC.

 

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1989 300E; 2004 ML350; 2007 E320 4Matic
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Discussion Starter · #3 ·
Get a scanner and read codes then look at actual values in AAC.

I will scan using the Autel MaxiAP200M bluetooth scanner tomorrow and will post back tomorrow - hopefully that scanner is good enough to read any AAC codes and values.
 

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W163 and General M Gremlin
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Was the R134a ever refilled in past (possibly with some dye)?
If so, take a black UV light to the areas under the hood, ac compressor areas and lines, to see if you see any leaking.
If not, when re-filling, include some dye, moving forward. Some, not all, suicide cans may have the dye infused in the cans.

Don't forget - you have a drier that may need attention too.
(fyi- not a fan of suicide cans for the inexperienced in AC dyi, just a comment made for knowledge)
 

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1999 E430; 2005 ML500
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Assuming the gage readings are accurate, you have no R134a. Getting to 0 psi would indicate a sizable leak, worth repairing before you recharge. So, first step would be finding the leak via a leak check.
 

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I will scan using the Autel MaxiAP200M bluetooth scanner tomorrow and will post back tomorrow - hopefully that scanner is good enough to read any AAC codes and values.
To evaluate condition of compressor you need to take belt off. Problem with refrigerant leaks is oil leaks out of the system as well. With no flow compressor will seize.
You can check for leaks using nitrogen and soap spray.
 

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1989 300E; 2004 ML350; 2007 E320 4Matic
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Discussion Starter · #7 ·
Below are the scan results:

041 N22b1 (interior temp sensor) 95.00F
042 (Blower voltage in Rear) 0V
043 B10/6 (Evap Temp Sensor) 77.00F
044 B12/2 (Refrigerant Pressure and Temp Sensor): 29.008 psi
045 B12/2 (Refrigerant Pressure and Temp Sensor) 122.00F
046 B10/7 (Rear Outlet Air Temp Sensor) 87.8F
047 B10/25 (Front Footwell Outlet Air Temp Sensor) 95.00F
048 B10/24 (Center Vent Outlet Air Temp Sensor) 95.00F
094 A9 (A/C Compressor) -0%
090 A32m1 (Blower motor) Specified Value 37%
091 A32m1 (Blower Motor) Actual Value: Reached
092 M2/1 (Rear blower motor) Specified Value 0%
281 A32n1 (Blower Regulator Short circuit cut-off): Inactive
282 A32n1 (Blower Regulator Maximum Current Limit): Inactive
283 A32n1(Blower Regulator) 100%: Inactive
284 A32n1 (Blower Regulator) Overload-Shut off: Inactive
285 A32n1 (Blower regulator): Temperature: OK
287 Undervoltage/Overvoltage detection (supply voltage) Inactive
288 Output Stage: Active
289 A32n1 (Blower Regulator) Current Consumption of component 'A32m1 (blower motor): 2A
290 A32n1 (Blower regulator): Temperature 96.80F
291 Supply Voltage A32 (Heating Systems recirculated air unit) 9.7V
050 Power Supply 9.5V
095 Stationary heater (STH) Off
096 R22/3 (Heater Booster) Off
097 M13 (Heating Water Circulation Pump): On
098 Rear Window Defroster Off

All these readings were taken with the Key in Ignition position 2, Engine off.

There were also Stored codes for the Motor flaps. I cleared those out. There are no other fault codes related to the AAC or Airconditioning.
 

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1989 300E; 2004 ML350; 2007 E320 4Matic
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Discussion Starter · #8 ·
I don't believe the system was ever refilled with a dye based R134A - the car was down in Dallas with my son for a couple of years and he just drove it with the Windows open until one day the belt broke last summer while he was driving back from Austin to Dallas - he decided he wasn't going to deal with multiple repairs on a 17 year old car and just went and bought a Honda... I had the car transported back to DC so I can keep it as a workhorse for all my other projects (wood working etc.).

I have some questions though...

1. How hard is it to remove the Serpentine belt and then to reassemble it to be able to check the compressor operation? I am at home and don't have access to a lift. Assuming I am able to loosen the belt, how would I check the compressor operation?

2. I don't have access to Nitrogen - where could I do that - at a gas station where they fill Nitrogen into tires? any suggestions and how much would I need?
 

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I don't believe the system was ever refilled with a dye based R134A - the car was down in Dallas with my son for a couple of years and he just drove it with the Windows open until one day the belt broke last summer while he was driving back from Austin to Dallas - he decided he wasn't going to deal with multiple repairs on a 17 year old car and just went and bought a Honda... I had the car transported back to DC so I can keep it as a workhorse for all my other projects (wood working etc.).

I have some questions though...

1. How hard is it to remove the Serpentine belt and then to reassemble it to be able to check the compressor operation? I am at home and don't have access to a lift. Assuming I am able to loosen the belt, how would I check the compressor operation?

2. I don't have access to Nitrogen - where could I do that - at a gas station where they fill Nitrogen into tires? any suggestions and how much would I need?
Put car on stands. From the bottom turn tensioner counterclockwise and arrest with 5 mm pin. Large steel nail will do. Slip belt off compressor pulley and turn it by hand. Both pulley and center shaft must turn together.

Forget nitrogen. That requires tank, regulator and hose adapter. Pressure needs to be about 250 psi.
Instead evacuate for an hour and shoot one can in it. Heat can in hot water first, hold it upside down. That should put enough refrigerant in to start looking for leaks.

In your live data readout battery voltage shows @9.7V. Why?
 

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Discussion Starter · #10 ·
I was wondering the same myself-- why A32 is showing 9.7V and test 050 is showing 9.5V. Maybe I left the key on in position 2 for about an hour and it pulled down the battery voltage - I will check the battery voltage tomorrow after I do the leak test. I am waiting for the dye to arrive from Amazon.
 

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I was wondering the same myself-- why A32 is showing 9.7V and test 050 is showing 9.5V. Maybe I left the key on in position 2 for about an hour and it pulled down the battery voltage - I will check the battery voltage tomorrow after I do the leak test. I am waiting for the dye to arrive from Amazon.
You need to connect battery charger now!
 

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Discussion Starter · #12 ·
Thanks - good call. I put it on the charger tonight and will leave it on all night on my driveway.
 

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Discussion Starter · #13 ·
So getting deeper into the mess..I pulled a vacuum from the low side for 90 minutes - with the pump connected and ports open it showed 29 mm of vacuum - as soon as I closed the low side valve on the manifold the pressure went up to 0 almost immediately... so it's pulling a vacuum when the pump is connected but it is not holding the vacuum at all. I tried the same on the high side and got almost the same result but was hard to tell since the gauge only drops a little for the vacuum on the high side. Then I decided to use my compressor to put in about 100 psi of air through the high side. After closing the manifold valves, the high pressure air held for an hour without dropping on both the high side and the low side. I am very confused as to why the high pressure will hold but the vacuum immediately drops off.

Then I decided to just look around all the fittings with my UV light and someone must has have put dye in it at some point because I saw bright green fluorescent circles on the firewall around both tubes where they go into the expansion valve. I also see a bright green fluoroscent circle around the inlet fitting of the compressor. I don't know how old that is and if I need to somehow clean it out and then try to add more oil+ dye and check again... the issue is that I cannot get the compressor to kick in at all so not sure how I could even add any (refrigerant + dye) or (oil + dye) - there just isn't enough suction in the system to pull the freon or oil... tomorrow I will try to do the method Witek suggested by heating the can in warm water and to build some pressure to force the gas into it but I worry that may not work because of the unknown leak....
 

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Discussion Starter · #14 ·
Ok _ I tried pulling in some refrigerant with dye but the compressor did not come on. The UV light showed some old Green dye around the evaporator valve and on the low pressure inlet connection of the compressor. I have ordered a new evaporator valve and it should arrive later this week and I will change it out on Thursday or Friday.

Meanwhile, I have another related curious issue that I need some help on... The white wire on the coolant recirculation pump always is hot - even with the car switched off for a couple of hours. Looking at the circuit diagram I am thinking it should not be hot (12V) if the car is switched off for a while but maybe this design is that it always has 12V on the white wire and that the Ground is switched on and off somehow through some other way - I am not sure... Can anybody guide me on if this is correct and how to check it and determine if there is a wiring fault or other control unit issue - I will replace that pump but if there is a wiring issue then I'm afraid it will just burn out the new pump...
 

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'07 ML350, '05 ML350SE, '04 ML350, '01 ML55, '05 SLK350, '04 SLK200, '76 280SL
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You don’t say if there is a problem or not with the recirculating pump? Ordinarily above a certain water temperature the pump will run on for a few minutes after engine shutdown. You speak of a constantly hot wire ( I assume you mean present voltage, not high temperature) but you don’t say if your pump is always running, sometimes running or never running. Can you clarify please?
 

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Discussion Starter · #16 ·
Pump is never running but there is a constant 12V on the white wire on the connector for the pump. The brown wire has a good ground contact. I checked with both a test light and also my Voltmeter. I am fairly certain the pump is shot so that's why it is not running when connected but also wondering why there is constant 12V on the wire with the car off for a couple of hours.
 

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'07 ML350, '05 ML350SE, '04 ML350, '01 ML55, '05 SLK350, '04 SLK200, '76 280SL
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Pump is never running but there is a constant 12V on the white wire on the connector for the pump. The brown wire has a good ground contact. I checked with both a test light and also my Voltmeter. I am fairly certain the pump is shot so that's why it is not running when connected but also wondering why there is constant 12V on the wire with the car off for a couple of hours.
I think you will benefit from reading all of this thread. It sounds like your pump is shot - so gloss over the bits about changing pump motor brushes - but the thread goes a long way to explaining conditions when the pump should run, as these are not just limited to run-on for a few minutes after shutdown. Understanding these conditions may take you one step closer to diagnosing. The second thread also contains some useful tests/fixes. A relay is probably at fault.


 

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So getting deeper into the mess..I pulled a vacuum from the low side for 90 minutes - with the pump connected and ports open it showed 29 mm of vacuum - as soon as I closed the low side valve on the manifold the pressure went up to 0 almost immediately... so it's pulling a vacuum when the pump is connected but it is not holding the vacuum at all

This could indicate a leaky Schrader fitting.
 

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Discussion Starter · #19 ·
RJV - thanks for the link to the excellent thread on the Aux Cooling pump. I have ordered a new pump from Amazon this morning. I read through the entire post (all 9 pages of it) and the coolant circulation pdf posted by 43sqd and see that the pump can run in a couple of other conditions but now I need to understand if those conditions exist on a 2004 model year ML350.. specifically

1. "Stationary heater/ON". How do I turn the Stationary heater on or off in my car?
2. "Enable conditions at residual engine heat complied with". Is this something automatically detected by the sensors in the car or is it some switch settings that I have to set?

This morning there is no voltage on the auxiliary pump connector so it did go down to zero overnight which is good but it had stayed on for more than an hour yesterday so trying to figure out what kept it on... anyway, I know the pump is bad now and I will replace it on Thursday - just worried about burning it out if the new one stays on for an extended period of time...
 

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'07 ML350, '05 ML350SE, '04 ML350, '01 ML55, '05 SLK350, '04 SLK200, '76 280SL
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RJV - thanks for the link to the excellent thread on the Aux Cooling pump. I have ordered a new pump from Amazon this morning. I read through the entire post (all 9 pages of it) and the coolant circulation pdf posted by 43sqd and see that the pump can run in a couple of other conditions but now I need to understand if those conditions exist on a 2004 model year ML350.. specifically

1. "Stationary heater/ON". How do I turn the Stationary heater on or off in my car?
2. "Enable conditions at residual engine heat complied with". Is this something automatically detected by the sensors in the car or is it some switch settings that I have to set?

This morning there is no voltage on the auxiliary pump connector so it did go down to zero overnight which is good but it had stayed on for more than an hour yesterday so trying to figure out what kept it on... anyway, I know the pump is bad now and I will replace it on Thursday - just worried about burning it out if the new one stays on for an extended period of time...
I think you need to monitor and measure more before you instal a new pump. Clearly the circuit does in fact switch off eventually - before you thought it never switched off.

Use your car and measure at different times and record engine temp, timing of engine shut down and follow up with whether pump circuit is on/off. “More than an hour” is not specific - is that 61 minutes or 261 minutes?

The more rigorous your monitoring the better the advice can be. You don’t want to have to replace the AAM on just a hunch.

Skipping this step and installing a new pump could just end in tears, again.
 
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