I found this post- see reply #15 where a procedure to test the servo motor is explained.

http://www.peachparts.com/shopforum/showthread.php?t=194635&highlight=checking+ACC+servo

I tried it and my wires got really hot, really fast! And the motor wouldn't run...

Not sure why they got so hot, but it appears that I clearly have issues with the servo...

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

if that is the case then the replacement unit may have damaged the amp, so be prepared to possibly have to replace that unit also

__________________
1967 250 S
1967 280SE
1968 250S
1971 280 SE
1973 220
1974 280 S
1975 450 SEL
1976 220 D
1979 300SD
1983 300 SD
1985 230 TE euro
1986 280SL
1986 500 SEL euro
1986 190E 2.3
1990 300 SE
2003 C230 K
2004 C230 K
1987 560SEL
1987 300SDL now in canada
2005 C230
1998 C43 AMG Sold to DON
1993 190E 2.6
300TD Former daily driver Totaled
current:
R320 CDI
Ram 2500 Cummins

A couple of operational questions - 1) does the servo motor run at all when the system is on A/C? I still have good A/C...

2) Also, if there is an air pocket, would this prevent the servo from operating?

3) Will the heat even operate in this car if ambient temps are in the 90's?

4) Would a bad auxiliary water pump contribute to this problem?

I am just not yet convinced that this rebuilt servo is bad - I tested the old one by connecting a 12v source to the leads on the servo (according to the above link), and the old motor didn't run either. Now it's possible that if the servo doesn't operate while the system is cooling, maybe that old servo is/was bad as well - since I haven't operated the heating system since Feb/Mar.

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

1. depends on the wheel temp, if it need to warm the air yes
2. unit should cycle even if there is an air pocket
3. yes
4. no, the aux pump will only run when temp is below specific temp

__________________
1967 250 S
1967 280SE
1968 250S
1971 280 SE
1973 220
1974 280 S
1975 450 SEL
1976 220 D
1979 300SD
1983 300 SD
1985 230 TE euro
1986 280SL
1986 500 SEL euro
1986 190E 2.3
1990 300 SE
2003 C230 K
2004 C230 K
1987 560SEL
1987 300SDL now in canada
2005 C230
1998 C43 AMG Sold to DON
1993 190E 2.6
300TD Former daily driver Totaled
current:
R320 CDI
Ram 2500 Cummins

According to what I have read on here, a bad auxilliary pump can take out the amp. So if your pump motor doesn't run when fed 12 volts directly, it could have damaged your amp. Some people put a fuse in the auxilliary pump line to avoid this problem.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

OK, made some progress, but I'm not sure how or why??

I finally figured out how to check the servo motor - connect battery voltage, negative to pin 4 and positive to pin 5 of the servo for full heat, and vice versa for cooling (Thanks to George Murphy!). Servo motor runs fine. Tested the aux pump with direct battery voltage and it runs fine - started the car and now I have heat and cooling! I can also clearly hear the servo running, resetting to the Park position when you turn off the ignition. I did put the front wheels up on ramps, to try and help get air out of the system - maybe that helped. Or maybe I just needed to "jump start" the servo motor (the thing was purchased several years ago as a back-up and never installed).

Anyway, so far so good...

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE