Trim a few wires off for a snug fit. Try changing the battery in your DVM unless you have recently... Seems odd. Solder the wires in with plenty of length then test to the installed wires

Try applying 12v to Trace #7 and ground to Trace #4 (perhaps use a fuse), Can you measure 12v across those two unidentified pads in 20v DC range.

Alan

 

That's a negative. Can't find voltage across that. Hooked a battery via alligator clips to the pins on the board and tested. I'll add the wires on now and re-test. I've got the contacts pretty clean now so I don't think it will change the result but you never know until you try.

 

Wires on but same result for both continuity and voltage testing. Would it be worth connecting the relay and see what happens? I have spares.

 

Here's your relay spec; file:///Users/macminici7/Downloads/mech_eng_dk.pdf

Pins 1 & 8 are the coil pins (720 ohms), with pins 3/4 and 5/6 as contact pins.

 

misspost - wrong thread

 

Thanks both, am out for the day today so will have to tackle finishing this one weeknight this week.

 

After spending the summer driving with AC bridged permanently on, now it's winter my wife complained it's cold in the car and I thought I'd better get around to soldering the new relay in. So last night I sat down to do the job, a bit fiddly, and I'm not proud of how elegant the joins look, but they are solid. Back in the car and a quick test this morning and no AC. Possibly I've not correctly followed the instructions but need a bit of help figuring our where. What have I done wrong? Also not getting any warm air, might not be related, water valve appears to be working ok.

Viewing the photo, pins on the relay in reading order are (top row) 1, 3, 4, and (bottom row) 8, 6, 5.

 

The connections look wrong to me (though its hard to see):

Coil looks to be connected incorrectly should be HVAC pins 4 & 5 [to relay pins 1 & 8 (either way around)]

Switch contact set between HVAC pins 5 & 6 [to relay pins 5 & 6 (either way around)] seem to be OK though HVAC pins 6 & 7 looks like they could be shorted?
Switch contact set between HVAC pins 8 & a diode after HVAC pin 9* [to relay pins 3 & 4 (either way around)] seem to actually just be connected to HVAC Pins 8 & 9.

* this appears to actually be HVAC pin 12 - though that is shown as a no connect on the wiring diagrams.

Alan

 

Thanks Alan, rookie error having 5 & 6 round the wrong way, now fixed.

For part 2, I'm not fully following. I have Relay pin 3 connected to HVAC8. Relay pin 4 connected to HVAC9 on the HVAC pin side of the diode. Are you saying these need to be reversed? Or connected somewhere else?

EDIT:

Seeing as it would only take a few mins, I reversed the 3&4 connections, still no AC. I guess you meant change the location then, but I'm not following the to where.

Double checking, when you are numbering HVAC edge connectors, which end are you starting from? I am starting from the left or top in the above pictures.

 

Actually I was looking at the later GTS head unit so ignore what I said - your '90 has a slightly different configuration on the coil & switch on pin 9.

Change the coil to be connected to HVAC pins 4 & to HVAC pin 7 via a diode [to relay pins 1 & 8 (either way around)] (so just change the coil wire from HVAC 5 -> HVAC 7 after the diode)

The switch contact set between HVAC pins 5 & 6 looks good [to relay pins 5 & 6 (either way around)] though HVAC pins 6 & 7 looks like they could be shorted - check?
The switch contact set between HVAC pins 8 & HVAC pin 9 looks good [to relay pins 3 & 4 (either way around)]

Sorry for the misleading guidance

Alan

 

That's a Fiber Optic and it illuminates the Numbers, the **** is not Illuminated, just slid it into the hole.

 

Thanks Alan, any advice is welcome :-)

Just want to be super clear on what I'm changing. Currently I have Relay pin 4 attached to HVAC5. You are saying move this one to HVAC7? If so, I have Relay 8 going to HVAC7 but on the end of the diode furthest from the HVAC edge connector. So I would need to attach Relay pin 4 to the HVAC connector edge end of the diode, does this sound right? Loren's diagram has an arrow from HVAC6 to Pin 5, and also an unlabeled arrow to HVAC 7. I assumed that as the bridge to made the AC work was between HVAC5&6 that it was likely to be 5 I should connect to.

HVAC6&7 have looked that way since I first opened it, given it worked before I'm trusting they are not shorted.

 

No HVAC 5 & HVAC 6 are the switch connections used for the jumper to make the AC run all the time. you already have those connected to the relay switch correctly - this is not related to the coil.

In your photos you have the coil (relay pins 1 & 8) connected to HVAC 4 & HVAC 7 via a diode this is in fact correct.

Check electrically that pins HVAC6 &HVAC7 are not shorted together.


Alan

 

Wires rechecked, I think I have everything right. Tested 6&7 with multimeter, no short detected. Still not working. Unless there's something I've done wrong on the wiring (which is always very possible - updated wiring pic included in post) I'm starting to think it's time to buy a reconditioned unit and replace this one.

 

Can you test the diode on HVAC pin 7?

Try also applying 12v to pin 7 and ground pin HVAC pin 4 - do you hear the relay click if not apply 12v to HVAC Pin 11 - click?
You can also try applying 12v to the other side of the diode on HVAC pin 7 (where your connection is).

If none of this works there must be a problem with the relay ground on HVAC pin 4* OR the relay doesn't work

*Test continuity between the relay pin and the edge connect 'land'

Alan