1984 300SD Climate control gremlins

[peragro]

Well folks, still troubleshooting the ACC problems that began with a non-functioning heater.

-Heater brushes replaced, it works when hooked directly to 12V.

-Monovalve repair kit installed as I've been having odd heat issues for the last year.

-1 amp fuse placed in line between aux. coolant pump and ACC (brown/green wire)

-Pulled out PBU (push button unit/AKA ACC) and took it apart. Temperature gauge was falling apart. Ordered a rebuilt one that arrived today. Installed it after checking resistance between pins 9 and 10 (Left side) to make sure that aux. coolant pump is ok, got 26 ohms.

And now, the current wall on which I am banging my head: (all testing done by pressing defrost to get default heat and high fan)

The new (rebuilt) ACC seems to work better than the old one but only when ignition is in accessory a few seconds after glow relay goes on. When engine starts blower motor cuts out. I can put the key in accessory setting without starting the engine and play with the ACC and get all options. A/C compressor comes on, fan blows multiple speeds, defrost kicks out heat and puts fan on high. As soon as I start the car I get nothing, it's like the ACC dies. Then when I turn off car and turn to accessory I get working ACC.

Don't know if it's related but when I turn ignition to accesory. I get 6 quick flashes of the interior dome light followed by 2 steady flashes that don't stop until the car turns on. I searched high and low for what that might mean but came up dry. Seems like it's some kind of code but I have no idea what.

I also have a picture of an orphan wire that lives in the area of the monovalve and aux. coolant pump. I'll try and upload some pictures later tonight. Hopefully someone can tell me what it is/goes to/does.

Much appreciate any help that folks can send my way.

[peragro]

Here's the mystery wire. It's part of the same harness that goes to the monovalve and aux. coolant pump.

[Hit Man X]

I'm curious about that wire too...

[peragro]

Looks like we'll have to remain curious for a while longer...

[speedy300Dturbo]

That thing has nothing to do with the climate control. It's an alarm contact switch for the hood, and yours appears broken from what I can see in the picture.

[peragro]

Originally Posted by speedy300Dturbo

That thing has nothing to do with the climate control. It's an alarm contact switch for the hood, and yours appears broken from what I can see in the picture.

Thanks for clearing that up. You're right it's definatly broken. When I moved it the whole thing pretty much fell apart. I just kinda taped it together and stuck it down in the firewall. Now I'm thinking I'll just forget about it.

[meltedpanda]

if you are getting irregular function or normal function when you fiddle with the key then the contacts in the iginition switch is most likely the culprit.

[Brian Carlton]

I'll study the wiring diagram when I return home tonight or tommorrow, Matt.

A question:

There are three positions on the switch: I, II, and III.

I is normally the "accessory" position.

II is the "run" position.

III is the "start" position.

Does the blower and CCU functions work only in position I, or will they also work in position II, prior to the start?

[meltedpanda]

if the acc is on, I believe it will function in number II position.
If fiddling with the key while in the II position while the car is working and either turns on or off the ACC then you can be sure the issue resides with the keyway/contacts

Other rare, but equally frustrating, causes is a bad engine temp interlock, located somewhere around the thermostat housing. If it is failing or near failure it will cause strange on /off behavior . It basically is the sensor that tells the system to turn on.
I know because this was my gremlin, after months of swithing out parts , acc units and the like.

[peragro]

Originally Posted by Brian Carlton

I'll study the wiring diagram when I return home tonight or tommorrow, Matt.

A question:

There are three positions on the switch: I, II, and III.

I is normally the "accessory" position.

II is the "run" position.

III is the "start" position.

Does the blower and CCU functions work only in position I, or will they also work in position II, prior to the start?

Thanks for the clarification in terminology Brian. It is indeed the II position which allows function of the ACC. Movement to III results in no-function. As meltedpanda points out I'm almost sure at this point that the ACC problem lies in the ignition switch. Upon further fooling with things yesterday I found I could turn on the ACC with wiggling the key sometimes.

So, does this mean I should change out the ignition cylinder and the ignition switch or one or the other? BTW, what kind of homemade tool can you use to remove the intrument cluster?

[peragro]

Originally Posted by meltedpanda

if the acc is on, I believe it will function in number II position.
If fiddling with the key while in the II position while the car is working and either turns on or off the ACC then you can be sure the issue resides with the keyway/contacts

Other rare, but equally frustrating, causes is a bad engine temp interlock, located somewhere around the thermostat housing. If it is failing or near failure it will cause strange on /off behavior . It basically is the sensor that tells the system to turn on.
I know because this was my gremlin, after months of swithing out parts , acc units and the like.

I'm going to change out either the ignition cylinder or switch, probably both. If things don't clear up after that I'm headed to the engine temperature interlock. Invaluable information Panda, thanks.

[meltedpanda]

No problem, and good luck, There is a testing procedure for the temp sensor, I will look in my notes.
I think if you search for cylinder removal procedure you should see how to do it. Give it a try
On mine I fabricated a tool and spent a lot of time trying to get it out but I just could not achieve the release. I ended up getting a new cylinder from an online parts store, (needed my VIN) and took it up to the local MB folks who got it out in a flash and replaced it. Looking back I think the tool I made was a bit whimpy. I probably also could have had a local locksmith remove it as well

[Brian Carlton]

Originally Posted by peragro

Thanks for the clarification in terminology Brian. It is indeed the II position which allows function of the ACC. Movement to III results in no-function. As meltedpanda points out I'm almost sure at this point that the ACC problem lies in the ignition switch. Upon further fooling with things yesterday I found I could turn on the ACC with wiggling the key sometimes.

So, does this mean I should change out the ignition cylinder and the ignition switch or one or the other? BTW, what kind of homemade tool can you use to remove the intrument cluster?

Yep, you've confirmed that the ignition switch is the culprit. But, it's probably not the cylinder........although.......if it is the original cylinder........you ought to change it. I finally changed the cylinder on the SD and, the old one literally disintegrated in my hands on removal.

I consider myself blessed by the M/B gods. If it jammed, I'd be in a world of hurt.

I'll double check the wiring diagrams tomorrow........but........I'm almost certain that the switch is the problem.

To remove the cluster, just take off the driver's kick panel and reach up and force the cluster forward out of it's home. I've never had much luck with the homemade cluster pulling tools.

[peragro]

Originally Posted by Brian Carlton

Yep, you've confirmed that the ignition switch is the culprit. But, it's probably not the cylinder........although.......if it is the original cylinder........you ought to change it. I finally changed the cylinder on the SD and, the old one literally disintegrated in my hands on removal.

I consider myself blessed by the M/B gods. If it jammed, I'd be in a world of hurt.

I'll double check the wiring diagrams tomorrow........but........I'm almost certain that the switch is the problem.

To remove the cluster, just take off the driver's kick panel and reach up and force the cluster forward out of it's home. I've never had much luck with the homemade cluster pulling tools.

Yep, it's the original cylinder as far as I know. I've been meaning to change it anyway. It's been acting a little squirrelly. I guess I'll go ahead and order a new ignition switch and cylinder sometime next week. I have to go out of town this weekend with the family. Thankfully I can get some heating or cooling if I wiggle the key here and there although I don't expect we'll need it too much in LA.

[Brian Carlton]

Originally Posted by peragro

Thanks for the clarification in terminology Brian. It is indeed the II position which allows function of the ACC. Movement to III results in no-function.

Check this again, please.

Position III will typically allow no function of any of the accessories during start including the CCU and the radio.

If the CCU and blower function in position II, then it's operating normally.