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  #1  
Old 09-02-2010, 10:59 PM
Hit Man X's Avatar
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Thumbs up 300SD HVAC questions/problems

Now that the A/C is working again in my SD, I am back to figuring out a few issues with my first gen system.

First off, my fan does not work on the Low setting (High and Auto work fine). I have narrowed this to, I believe, the fan resistor pack. I am looking at Page 13 on the PDF 83-603... the blower fan itself is new as of last summer and my main climate push button unit is a Programma reman from around 2002-2003.

Are there any specific tests to run on the PBU to verify if it works? The five buttons work as they are supposed to as does changing the temperature on the wheel. Just there is no fan speed on Low, this is with a visual check inside the blower box. The system feels like it is operating on a medium fan speed with only ambient air going across the condenser to try to cool down.

One of my other issues is that the main/recirculation door does not open toward the front of the car when the A/C function is switched on. My vac pods are new as of last year. It does at times just at random times close and the fan speed feels like it kicks up. Page 7 on PDF 83-604 points to a potential fault in the switchover valve for the main flap (large stroke), I have yet to check this and pull a vac on the lines from there to the pods.

Next, does anyone know what part number '000 822 09 03 88' is responsible for in the system? It is only a first gen part and I am having trouble finding what it is for, let alone if I can test the unit. It is silver with 12 pins.

Lastly, what the hell is the Scoop flap for in the system?



I feel like I have a combination of minor issues and need to test before I just start throwing money at a problem.

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  #2  
Old 09-02-2010, 11:06 PM
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There's another control unit which is the brains behind the operation. I'm guessing that's what the 12p unit you found is for. I'd also give the resistor pack a look. It lives under the brake booster.

-J
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  #3  
Old 09-02-2010, 11:26 PM
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Alright heres what I got:

1) Low Speed not working --> most likely resistor pack.

To check if PBU is signaling low speed:
Test voltage at YL/RD, "SPEED 1 INPUT", pin 2 of speed controler (0038203910 is pn). You should see some voltage here. I'm not sure what it *should* be. I'd say probably around 12 maybe? If you get nothing then I'd suspect PBU.

If you do get a voltage at that pin, then [b] to check stage 1 resistor output[\b]
Test for voltage at pin 6 of the speed controller. if you see voltage (4v according to fsm) then it should be working fine. However if you don't then replace the resistor pack as thats the problem.

diagram:
http://imgur.com/J0DED.png

2) Operation of recirc/scoop flaps:

Not as details as I'd like...

3) As for the mystery box. I couldn't find it in the EPC, but I noticed there are two "electronic control box"es on the blower motor housing. One is for blower control, one is for temp control...your mystery box could be one of those...

Item 19 top picture, Item 9 bottom picture
http://imgur.com/u0t2O.png

Hope that helps.
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82 300SD 145k
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  #4  
Old 09-02-2010, 11:29 PM
JamesDean's Avatar
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Posts: 5,034
Quote:
Originally Posted by compu_85 View Post
There's another control unit which is the brains behind the operation. I'm guessing that's what the 12p unit you found is for. I'd also give the resistor pack a look. It lives under the brake booster.

-J
You're referencing the auxiliary fan preresistor.

The resistor pack for the blower is located in the blower control unit as per the FSM. ACC83-85.pdf#page=13

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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