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E320 Yr 2000, S430 YR 2002
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Discussion Starter #21
As you can see, I am a novice at AC systems. I am just learning about them. I tested the compressor clutch by connecting to a 12V battery and its fine, the clutch engaged.Going down one level, I read about the pressure switch (3 pins) which may be bad. I am not sure which pins need to be shorted to do the test.
I get the following values from the diagnostics:

I can post diagnostic values, which I had posted many times on another thread without getting anywhere. I decided to change all components of the AC system and recharge. I have a new compressor, expansion valve, condenser and Receiver dryer.-- yes, its a shotgun approach, but the car is 20 years old, so I thought I would change everything and learn things.
 

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As you can see, I am a novice at AC systems. I am just learning about them. I tested the compressor clutch by connecting to a 12V battery and its fine, the clutch engaged.
Keep at it. Power up compressor and finish charging 1000 grams. Post manifold gauge values when done. 40/250 HI/Lo is about right. Temperature dependent.
 

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Discussion Starter #23
I was only able to get 790 g of Freon into the system. Eveb with teh compressor forced on with Jumper, only 148 g from the last can went in. As soon as the compressor is reconnected normally into the system it does not engage any further.
 

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What were pressure readings on manifold gauge with compressor forced on?
 

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Discussion Starter #25 (Edited)
The manifold gauges show the following: Lo side 12 PSI, HI side 12 PSI -- compressor not engaged.Temp here is 65F
 

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Discussion Starter #27
I think I must have developed a leak? I can understand that the high pressure is zero, because the compressor does not engage, but I have no idea why the Lo is now almost zero.
Anyway, this is my weekend project, so all the borrowed equipment is now gone back to the store. I used new O-rings. matching them to the ones that came out, and used a torque wrench for the compressor hose fittings.. I will either go to a Mercedes Mechanic or try looking at things again next weekend. Is there a diagnostic for the Freon pressure switch or temp sensor at the evaporator.
 

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1998 E320 base sedan @ 160kmiles
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I was able to get a vacuum at about 30 psi, which held with the pump off for 2 hours.I am now trying to recharge the system. I was able to get about one can( 12 oz) of R134A into the system, but the compressor clutch still does not engage. I tried the P1+16 method but still no clutch engagement. Its a new compressor, so where do I go from here. I did clear all the error codes and I do not have the EC light on.
You do not add 16 to P1. You add it to P2, so your P2 should look like 152 (this is in the sensor menu, item # 43, I believe.

STAR TekInfo

Restore P1 to its original value. It may have messed up with the variant of the system.
 

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Discussion Starter #29
Matt, I engaged the compressor by supplying 12V to the compressor connection, however, I was surprised that it would not allow me to charge to the 1 kg value.If the compressor is controlled by the three pin pressure switch and the temp control on the drier then can these be used to force the compressor to go on ? Is there a way to check these switches ?
I had added 16 to P2 so its value went from 136 to 152. Now its back at 136. I have put in 790 gm on the low side. I thought the compressor would engage with this much Freon.What else could be keeping it from engaging ?
 

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1998 E320 base sedan @ 160kmiles
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The system we have do not have temp or pressure "switches". It has pressure and temperature sensors. This means that the sensors report what the pressure and temperature of the refrigerant is and the controller makes the decision to start the compressor or not. For the time being, do not worry about full 1 kg for the compressor to start. I should start with 790 grams. The problem could be the pressure sensor, or the temp sensor, or both. Maybe the sensors are OK but wiring / connector damaged. If the controller detects a bad sensor (electrically or by implausible sensor value), it will not start the compressor for compressor protection. Setting P2 to 152 bypasses the pressure sensor reading, but I am not sure what happens if the controller declares the sensor is bad. You need to post the sensor values (1 to 8) with the engine not running (key in position 2), and also post any fault codes that the controller detects. If the sensor values are plausible, and if there are no faults, set P2 back to to 152, turn the key to position 0, then position 2 again, and start the engine with a/c on. Then post the values.

I suppose you get cool air when the compressor is forced to turn on with 12V applied to the clutch coil ? You typically do not need to electrically test the sensors, as the controller does that for you.
 

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Discussion Starter #31
Hi Matt,
at 58F, engine off, first thing this morning; compressor not on
1 62
2 57
3 69
4 67
5 66
6 75
7 00
8 64
After driving for 15 miles at 55 F and waiting 15m ( had to be in a call) -- compressor not on.
1 73
2 78
3 100
4 98
5 75
6 188
7 00
8 27

When I forced the compressor on yesterday, unfortunately I was too busy looking at the compressor to see if cool air was coming from the vents !
By Pressure switch and the temp switch, I meant the sensor which switches on the compressor through the control AC controller.
 

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1999 E320, 2000 E320, 2003 E320 Wagon, 2005 C230K SS, 2010 Accord LX w Eibach & Koni FSD's
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Hi Matt,
at 58F, engine off, first thing this morning; compressor not on
1 62
2 57
3 69
4 67
5 66
6 75
7 00
8 64
After driving for 15 miles at 55 F and waiting 15m ( had to be in a call) -- compressor not on.
1 73
2 78
3 100
4 98
5 75
6 188
7 00
8 27

When I forced the compressor on yesterday, unfortunately I was too busy looking at the compressor to see if cool air was coming from the vents !
By Pressure switch and the temp switch, I meant the sensor which switches on the compressor through the control AC controller.
#7 hows no refrigerant pressure. It all leaked out or sensor is bad.
Since system held vacuum for two hours, sensor may be bad and preventing compressor from coming on. But with 790 gm of refrigerant, you should have more than 12 psi.......leak? Did you lubricate O-rings with pag oil before installing?



After running #3 and # 4 shows slight coolant flow thru heater core. #8 went down.........maybe compressor kicked in briefly while driving?
 

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1999 E320, 2000 E320, 2003 E320 Wagon, 2005 C230K SS, 2010 Accord LX w Eibach & Koni FSD's
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I think I must have developed a leak? I can understand that the high pressure is zero, because the compressor does not engage, but I have no idea why the Lo is now almost zero.
When compressor is not running, hi and low side pressure will eventually equalize.
 

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Discussion Starter #34
May be the pressure switch has gone bad. Before the repair, the compressor clutch was engaging, but I thought that the compressor being 20 years old may be the problem in that it cannot compress anymore. Is there a way to test the pressure switch or at least the wiring to see if the switch was OK, the compressor would run ? It has three terminals on it, but since I do not know what each does, I do not want to put jumpers on them. I can measure the voltages, if I knew what they should be at the sensor wiring output. The other switch -- temp sensor is a two pin switch; does an open indicate over temp or does a short ?
 

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Premium Member
1998 E320 base sedan @ 160kmiles
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6,368 Posts
Hi Matt,
at 58F, engine off, first thing this morning; compressor not on
1 62
2 57
3 69
4 67
5 66
6 75
7 00
8 64
After driving for 15 miles at 55 F and waiting 15m ( had to be in a call) -- compressor not on.
1 73
2 78
3 100
4 98
5 75
6 188
7 00
8 27

When I forced the compressor on yesterday, unfortunately I was too busy looking at the compressor to see if cool air was coming from the vents !
By Pressure switch and the temp switch, I meant the sensor which switches on the compressor through the control AC controller.
To check the refrigerant sensor is simple. When you put the refrigerant in, and read the low side from the manifold gauge, the high side should be the same with a/c not running. You could have confirmed this when you recharged the system. If the sensor (item 7) read 00, then you could know the sensor or its wiring would have gone bad. It should have more or less the same reading as the high side of the manifold gauge when the a/c is running, or low side, if the a/c is not running.
 

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535 Posts
Discussion Starter #36
I read 0 for value 7, but the manifold gauges also read 0 on both sides.However, 790 g of refrigerant went into the low pressure port as measured by weight differences in the Freon cans. May be its all lost ? -- is that likely within a few hours ? The system did hold vacuum for 2 hours at least.

Very confusing.
 

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1998 E320 base sedan @ 160kmiles
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6,368 Posts
I read 0 for value 7, but the manifold gauges also read 0 on both sides.However, 790 g of refrigerant went into the low pressure port as measured by weight differences in the Freon cans. May be its all lost ? -- is that likely within a few hours ? The system did hold vacuum for 2 hours at least.

Very confusing.
Did you read zero on the gauge connected to low side when putting refrigerant in the system ? What happened immediately after charge with the a/c off ? Now, if you read zero and both the gauge and the sensor, then you have a huge leak.
 

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Discussion Starter #38
Matt,
I agree with your assessment. However, I did check that the system held vacuum for 2 hours -- of course that does not mean it did not develop a leak later. Perhaps at the weekend, I will try with another can and some dye. I do not want to get to the expansion valve again, but looks like I have no choice. If its an evaporator leak -- which understand is in the car, I do not even want to think about it. I checked the connections at the compressor, dryer and the condenser and they all seemed fine. Now that I have started this job and experienced quite a bit of pain, my best option is probably to carry on.
 

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1998 E320 base sedan @ 160kmiles
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Well, positive and negative pressures are two different things. When you apply negative pressure (vacuum), it may hold it, but when positive pressure is applied, especially when the compressor is running, it may leak. That is why it is always a good idea to put dye in the system right at the beginning, and check immediately after the system is vacuumed along with the refrigerant.. I have an in line add-on reservoir which allows me to pour some dye (that you can get from an auto store) when recharging with plain refrigerant. You can get refrigerant + dye in a can but they then to be more expensive. You need UV light source and yellow tinted glasses. For evap / expansion valve leak you could check the drain from the evap under the car. Hopefully a leak that you can fix. If you are sure it held the vacuum, it is not likely a hose, or pipe or evap leak, more likely an o-ring issue.
 

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1999 E320, 2000 E320, 2003 E320 Wagon, 2005 C230K SS, 2010 Accord LX w Eibach & Koni FSD's
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Going to ask again...............did you lubricate O-rings with PAG oil before installation?
 
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