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1997 E420
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11 Posts
Discussion Starter #1
Planned to add refrigerant with DIY kit, but did not because initial gauge reading was in red zone at 90 psi. During test, no error codes were noted, and troubleshooting showed refrigerant pressure (item #7) was 5 bars (approx 73 psi). Other items: #1 (inside temp): 37; #2 (outside temp): 25; #3 and #4 (heater core temps): 33 and 31; #5 (evap temp): 25; #6 (coolant temp): 63; #8 (refrigerant temp): 28; #24 (battery voltage): 11.4. Removed covers from duovalve and pushed pistons down. They moved smoothly and returned to original position. Advice/suggestions would be appreciated. rer1001
 

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1998 E320 base sedan @ 160kmiles
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6,678 Posts
Hello :).

Does your compressor run when you start the engine with the a/c on ? Your readings are with the engine off.
 

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1997 E420
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11 Posts
Discussion Starter #3
Hello :).

Does your compressor run when you start the engine with the a/c on ? Your readings are with the engine off.
Yes, it does. When I press the EC button, the clutch does not engage, and when I turn off EC, the clutch engages. Also, if there is something wrong with the compressor, would I get an error code? Thanks.
 

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1998 E320 base sedan @ 160kmiles
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6,678 Posts
What are the readings when you engage the compressor and with the engine running ?

Do you get 90 psi at the low side with the compressor running ?

If the clutch does not engage because of an electrical issue (blown fusible link in the clutch coil) you will get an error. If the compressor turns but does not accept refrigerant, that means there is an inherent problem with the compressor and/or expansion valve. You need to check the high side ( #7 or from the manifold gauge if you have any).
 

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1997 E420
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11 Posts
Discussion Starter #5
Hi, mrboca-
I took readings while the engine was idling at about 600 rpm, and they are not very different. #1/36; #2/26; #3/27; #4/27; #5/27; #6/67; #7/05; #8/25; #24/13.3. Notice that #7 (refrigerant pressure) stayed at 5 bars. Thanks again.
 

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1998 E320 base sedan @ 160kmiles
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6,678 Posts
If the compressor is turning and and the pressure stayed the same at 5 bars, obviously the compressor is is not compressing (meaning the pistons in the compressor are not moving). You have enough static pressure at the low side (5 bars) to start the compressor to compress, so #7 should go up even if you do not feed the compressor with more refrigerant. You cannot put more charge as the compressor is not sucking the refrigerant.

My opinion is that the compressor is bad (possibly the intake valve is stuck), or the expansion valve is closed. You could take it to a competent a/c shop to confirm.
 

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1997 E420
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11 Posts
Discussion Starter #7
Yes, the 90 psi reading on my DIY gauge is while the engine is at idle, A/C is on, and the compressor clutch engaged. If I press the EC button while the engine is idling, the clutch disengages, and the pressure seems to be slightly higher, maybe 100 psi. Hard to tell exactly, since there are no marks between 60 psi and 150 psi.
 

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1997 E420
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Discussion Starter #8
Thanks. I think our posts passed each other. Your diagnosis seems pretty straight-forward.
 
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