1998 W210 E300 climate control issues

[imryanmoriarty]

I've got a 1998 E300 turbodiesel I've owned for a few years and the A/C has never worked in it. I'm hoping to fix that!

I've identified two problems but have some questions:

1. My A/C clutch doesn't engage. I removed the electrical connector from the compressor and measured 4.4Ω coil resistance which seems reasonable. With defrost ON, I measured 7.8V to the coil. I took the A/C pushbutton control module (N22) loose and measured the same 7.8V going to the coil between wires #25 and #19. Seems like I need a new control module but I'm not 100% clear on the version coding for a replacement. Seems like I'll be able to use a functional control module from any W210 as long as I version code it correctly, but I'm not sure what my P1 value should be. Should it be 32 or 40 (8 + 32)? Any advice on sourcing a replacement control module?

2. My auxiliary fan doesn't work, even when I force it into full demand via control module (value #20 = 21.1). I took the fan motor connector loose and read an open circuit for the motor windings (obviously no good). The power to the fan coming from the "AIR control module" (N65/1) was kind of weird (it would sweep from ~4V to ~12V and repeat) but I'm not sure how it's supposed to function when it's driving the fan honestly. Seems to me I need a new aux. fan motor at a minimum. Any input on this part?

Appreciate any help you guys are able to give me on this. The way the climate control is setup on these things is a real headache. Thanks!

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Following is some additional information for reference:

I pulled DTCs from the A/C pushbutton control module (N22): b1231, b1234, b1235, and b1459. I reset them and they didn't come back.

In the version coding menu, I had P1 = 72 and P2 = 152. The P1 value didn't make sense to me so I changed it to P1 = 40 (8 + 32). I left P2 = 152 (8 + 16 + 128). This didn't fix my issue. [edit: per these posts on another forum, I've since changed the version coding to P1 = 08. Issues remain the same.]

In the displaying actual values menu on a hot day with the car idling and the blower fan at MAX, I got the following:

1 103
2 98
3 105
4 107
5 103
6 172
7 02 (this is low but I don't want to recharge the system until I'm convinced it can function)
8 109
9 27
10 5.0
11 3.1
12 4.1
20 3.2
21 42 (this is weird since it would mean I'm at 4200rpm; the value is changes with engine speed consistently but not by the factor of 100 the book gives [edit: apparently, this is normal])
22 00
23 32
24 13.1
40 85
42 40

[engatwork]

I think you have to at least have the correct charge in it before you can do much troubleshooting.

[imryanmoriarty]

Going off the attached snip from the 210 air conditioning diagnostic manual, I've got 7.8V to the compressor clutch coil with defront ON when I should have 11-14V (i.e., battery voltage). Seems to me it's trying to activate the coil right now so I don't think it would do any better with a recharged system.

I didn't repeat the test with the EC button ON, though. I should do that.

I could also just force 12V to the coil and see if it pulls in or not.

Also, re: version codes, I found this post on another forum which plainly states "If you car has aux fans in the front, the P1 setting should be 08." My car has aux fans so I just changed P1 from 40 to 08 but they still don't turn at all when forced to run (#20 = 21.1).

[engatwork]

Try putting 12 volts to the compressor long enough to see if it will pull in.

[engatwork]

I'd still evacuate, vacuum and charge the system to the design capacity.

[vince]

The system needs to be charged for the clutch to engage. And before doing anything I would pull vacuum on the system to determine if there is a leak. Vacuum should hold overnight or you are wasting your time with the clutch diagnostics. On the 210 evaporator leaks are fairly common.

[imryanmoriarty]

Turns out the N22 control unit was no good. I replaced it and evacuated/recharged the system and now my A/C is working normally.

I still need to replace the condenser fan, but I've got a replacement ordered that's supposed to be here Monday.

And just to confirm, the system does not need to be charged for the compressor clutch to engage. As long as EC is OFF, the N22 energizes the clutch coil automatically as long as you have +16 added to the N22's version coding P2 value.