GregBBRD

Could you guys help me out?

I'm trying to figure out where the year break is for different control units. There appear to be units with a single "economy" mode on the face and there are units that have two "economy" modes. The one with two "economy" modes has one with arrows points both up and down and another with an arrow only pointing down.

Could you look at your cars and let me know which model control unit your car has? Make sure you tell me the month and year of your car.

Landseer

Not to stop others from responding with a survey of their equipment....

But I did book research on this the other day, FWIW.

No Eco early years,

Then, optional single Eco w/AC 574 option, looks like it was introduced for 1980 model year , based on tech svc by year document for 1980.


Double eco looks like it took over for entire MY 82 according the tech svc by year document for 82 and extended through 1983 until June 10, 1983 build date, or VIN 92 DS 86 1952.

At that time, it appears that no-Eco 1984 unit was utilized in whatever 1983 cars were still being produced. (TB grp 87, no. 84-01, Feb 10, 1984) (excerpt below)

I have a double Eco unit from an 83 wreck, unsure of VIN, unsure of condition, yours free if needed.

GregBBRD

Wow, thanks. I suspected that someone on Rennlist would know the answer...Mark Anderson and I couldn't figure it out.

So, you think that the '84 models used the later model control head, like on the 1985 models?

I'd love to have that double eco model you have. These things are starting to get a bit harder to find cores for rebuilding. I'm taking pieces from multiple units and combining them to make good rebuilds. This will only get worse, as time passes.

Thanks,

greg brown

928 obsession

My '82 has the double eco control head, as does my father's '82. As Landseer pointed out the change occurred in '83. Also, if anyone can source the tiny AC relay located inside of these units, I could use two.

Landseer

Absolutely. Have two 84's in the driveway (third is on a campus like yours is ) and an 85 and 86 and the heads look the same and the wiring diagrams do too.

Just just PM where you want me to send it I'll mail it tomorrow. Its on my desk here and looks ok on the outside, but untested and internals are unknown.

There is a well-documented fix here on substituting a radioshack relay instead of the undersized relay, Christian. Its done off-circuit board, I think.
I know Dr. Bob has written about it.

928 obsession

I've read the documentation on replacing the relay on the newer HVAC head, but the earlier ones have only 3 contact points on the board instead of 6. I'll probably open it up again soon and pull the relay off the board this time to determine the wiring for an external relay.

Landseer

I bet Dr. Bob could help.

dr bob

GregBBRD

The relay in the early control heads doesn't serve the same function as on the later control heads (it doesn't switch the compressor on/off), so they don't fail at the same rate. The compressor control is off of another circuit and has a different failure mode.

We've built "testing fixtures" for both the early and late control units, using real components, so that we can make sure that every function of the control units works, before 928 International ships their rebuilt units. The rebuilt units get run through a test sequence that takes about 15 minutes, with "real loads". By doing this, we can be 100% sure that any problem the customer might be having isn't the fault of the control unit.

SeanR

I've been trying to piece together one working one out of a few of the old non working ones around here. These things are not the easiest ones to deal with. We need to do a work around so the later style will work in the early cars. I'm not holding my breath though.

928 obsession

If this relay pictured in the bottom left is not the cause, what other components fail in the early control unit?

GregBBRD

This should be fairly straightforward, and I'd be glad to look at it and see how to do it. Why do you want to be able to do this?

GregBBRD

Yes, relay doesn't control the A/C compressor on that circuit board. The power actually goes through the tracings on the board.

928 obsession

I checked out the tracings on the board and they all appeared to be connected and undamaged. Are there any other things to look for on this board? Just an FYI, every other function works on the unit, except for the AC. I've checked everything in the AC system and I'm not getting power to the anti-freeze switch, which shows the HVAC unit is not sending power.
Just out of curiosity if I'm unable to repair my unit; since the early HVAC unit does not have a manual push button to activate the ac compressor as the later units do, could I wire a switch out of an '84+ to activate the ac compressor? Thanks