1987 300td part/function?? HELP! - PeachParts Mercedes-Benz Forum

Hogweed · #1 09-03-2013, 09:41 AM

what is the function of the 3" long rectangular connection with the spring-like coil that is surrounded by a square ceramic housing?? located beneath the abs pump on the driver side inner fender; has wire connections on both ends. the one in this car broke and the connections are rusted.
this one is from a 300te gasser but it looks a lot like it and was located in the same place......could i use this one??
thanks
gh

Hogweed · #2 09-03-2013, 10:22 AM

for clarification.....i'm guessing it may be important since the car wont start now

kerry · #3 09-03-2013, 10:28 AM

I'd say it's a resistor and it's function is to resist. Beyond that I'm clueless.

Hogweed · #4 09-03-2013, 10:33 AM

bravo!! i used the term resistor and found images of the auxiliary fan resistor! bad news is, i'm guessing my no-start issue is not related to this......

Quote:

Originally Posted by kerry

I'd say it's a resistor and it's function is to resist. Beyond that I'm clueless.

kerry · #5 09-03-2013, 10:40 AM

I doubt the no-start condition is related to that resistor. On old Chrysler's bad resistors frequently caused no-start conditions but not on a TD I think. what are your no-start symptoms?

Hogweed · #6 09-03-2013, 11:04 AM

put the one in from the te and it started.....was fine until i started some rust repair in the area and that resistor fell apart leaving the rusted connectors hanging loose. i thought i remembered it being related to the a/c system so i didn't worry about it too much. it was up on the jack for a couple days and it wouldn't start when i went to take it to the body shop today.

Quote:

Originally Posted by kerry

I doubt the no-start condition is related to that resistor. On old Chrysler's bad resistors frequently caused no-start conditions but not on a TD I think. what are your no-start symptoms?

jcyuhn · #7 09-03-2013, 11:08 AM

That is most assuredly the fan resistor for the low speed operation of the electric cooling fan. The low speed is triggered by the red (or green) pressure switch on the a/c dryer.

High speed fan operation is a separate circuit triggered when engine coolant temp reaches 105C.

It definitely does not impact a no-start condition one way or the other.

Hogweed · #8 09-03-2013, 11:53 AM

not sure i agree. for whatever reason it didn't start when it was out and started up the second i put it in

Quote:

Originally Posted by jcyuhn

That is most assuredly the fan resistor for the low speed operation of the electric cooling fan. The low speed is triggered by the red (or green) pressure switch on the a/c dryer.

High speed fan operation is a separate circuit triggered when engine coolant temp reaches 105C.

It definitely does not impact a no-start condition one way or the other.

BrianCostello · #9 09-03-2013, 11:57 AM

It is the fan resistor.

Maybe it did not start because you had a loose 12v if nothing was connected.

Hogweed · #10 09-03-2013, 12:13 PM

yeah i was thinking it was aux fan or ac but not integral to the operation of the veh....cranked like a champ but no fire until i put it in.

Quote:

Originally Posted by BrianCostello

It is the fan resistor.

Maybe it did not start because you had a loose 12v if nothing was connected.

jcyuhn · #11 09-03-2013, 12:40 PM

Quote:

Originally Posted by Hogweed

yeah i was thinking it was aux fan or ac but not integral to the operation of the veh....cranked like a champ but no fire until i put it in.

That is very strange. That resistor does not even have power, it is connected to a relay in the fuse box. The relay is closed by the high pressure switch on the dryer. Closing the relay sends 12v to the resistor, causing the fan to run at low speed.

An '87 doesn't even need electricity for the engine to run. It uses a computer to manage the idle speed, but other than that it is a purely mechanical injection pump just like the older cars. I owned one of these for many years.

Hogweed · #12 09-03-2013, 12:49 PM

i'm with you on that. when it fell apart i didn't think i needed to replace it. when it didn't start i remembered it was out but still didn't think of it as causal. i only replaced it as a means to rule it out but then it started!!

Quote:

Originally Posted by jcyuhn

That is very strange. That resistor does not even have power, it is connected to a relay in the fuse box. The relay is closed by the high pressure switch on the dryer. Closing the relay sends 12v to the resistor, causing the fan to run at low speed.

An '87 doesn't even need electricity for the engine to run. It uses a computer to manage the idle speed, but other than that it is a purely mechanical injection pump just like the older cars. I owned one of these for many years.

kerry · #13 09-03-2013, 12:51 PM

I'd look for some kind of relationship to the glow plug system since I'm thinking inoperable glow plugs were causing the no-start condition.

Hogweed · #14 09-03-2013, 12:57 PM

that was what it was acting like. i suspect that the GP circuit draws off that somehow

Quote:

Originally Posted by kerry

I'd look for some kind of relationship to the glow plug system since I'm thinking inoperable glow plugs were causing the no-start condition.

gsxr · #15 09-03-2013, 08:30 PM

Quote:

Originally Posted by Hogweed

yeah i was thinking it was aux fan or ac but not integral to the operation of the veh....cranked like a champ but no fire until i put it in.

Completely unrelated. Pure coincidence. There is no connection between the fan resistor and the glow plug relay. Consipiracy theorists may disagree.