79 Seville climate control troubleshooting help

[Gene Beaird]

I've been trying to figure out why our Seville doesn't seem to be routing the air properly, and only blew cold air.  I recently acquired a tester, and that has helped figure out that I at least have voltage and vacuum to the controller unit, and that the tester can move the air-mix door, but I've not been able to get much further. 

As I said, with the tester connected to the climate controller, I can use the manual control knob to control the air-mix door.  When I reconnect the climate controller to the car's wiring, though, and start the car, even with the in-dash controls set to 'Off', the air-mix door moves to the full heat location and that's it.  No amount of moving the in-dash control settings, or adjusting the temp will move it from there.  It stays there even after turning the engine off, which I would kind of expect.

The air only seems to 'seep' out of the vents, not being properly routed via the dash vents, floor vents or windshield vents, no matter what the setting is on the in-dash control unit.  I am getting vacuum to the Climate Controller, but it appears to not be doing anything else.

I discovered a black plastic tube coming through the firewall next to the evaporator housing.  It was teed into vacuum from the engine, and the tee fed vacuum to the cruise control switch on the driver's side brace bar, another line went to the black hose in the firewall, and yet another vacuum hose went to the heater control valve.  I thought that line was for the heater valve, but when I rerouted things so that line went directly to the heater valve, I had no vacuum for the climate controller.  I re-routed it back so that that vacuum source feeds the cruise control and the climate controller.  The heater control valve is currently disconnected.  So, I need to find where that vacuum hose is.  Any ideas? 

So, as you see, it appears the climate system on our Seville is really messed up.  I need help. 

1. Why doesn't the air get properly routed out the appropriate vents depending on in-dash control setting?
2. Why does the air-mix door go to full heat when the key is turned on, never to move again, even though I can control it with the tester?
3. where is the vacuum source for the heater valve.  It appears to be a vacuum hose with a white stripe, according to the FSM.  Where does it come through the firewall? 

Thank you for any help.

[cadillactim]

When you use the tester to make the air mix door move, is the air flow out of the vents when in A/C and on the floor when in full heat?  If so, then the programmer seems to be working properly.

It sounds like you might have a sensor string problem. An "open" circuit in the sensor will drive the programmer to full heat, regardless of the temperature wheel setting. Likewise, a "shorted" sensor circuit will drive the programmer to full A/C.

With everything hooked up, and even though the programmer is in full heat, will the fan speed go to low speed when you set the dash control on Auto Lo? If, so then it sounds like a sensor string problem. If you can't control the fan speed, then you might have a problem with the dash control unit.

Tim

[Gene Beaird]

Well, that's good news, I guess.  Yes, as I move the in-dash controls from auto to low, and high, the blower speed does change.  And yes, it seems that the air is coming out the dash vents and floor vents, although it doesn't seem as strong as the blower is blowing things.

Oh yeah, when on auto, I think the tester documentation said that recirc air door should close.  It may take 5 minutes for some cars, but it should still move.  I _never_ saw the recirc door move.  This is the door that's in the passenger side kick panel to the right of the Climate Controller programmer unit. 

Where are these sensors located?  What do they look like?

I still have the heater control valve disconnected.  Any idea where that vacuum line should be?  Thank you.

[Gene Beaird]

<SNIP>

I still have the heater control valve disconnected.  Any idea where that vacuum line should be?  Thank you.

Found it!  It goes through the same bulkhead plug that a wiring harness and the ACC vacuum source goes through that's just inboard of the evaporator box in the engine compartment.  It was under the wiring harness, and had dropped downward.  Someone had plugged it with a screw, so I'm thinking a PO has had issues with the heat being on all the time. 

[waterzap]

Just want to add. Those climate control testers are still available online for pretty cheap. Around $50 or so. If you have a 70’s Cadillac, they all use pretty much the same climate control computers, which can be diagnosed with these testers.
Look for Tester J-23678 and harness J-24774
Just useful to have and to get while they are still available.

[Gene Beaird]

I'll second what Waldo says.  While there are folks on this forum who can and do repair the controller, it's really easy to verify the thing works, and to calibrate it when it needs a fine tune, or to determine for certain it needs to go out for service.  They're cheap, for now.

[Gene Beaird]

I finally got some time to go work on the Seville again today.  I'm trying to chase down the sensors now.  I located the ambient temp sensor, and it checked out at about 36 ohms.  That seems pretty good, given the temperatures today (upper-80's F). 

I can't find the in-car temp sensor, though.  IIRC it has two lt-green/blk wires going to it.  My FSM is out at my shop right now, though, so I don't know for certain.  I do find a two-wire connector located directly above the glove box, but it only has one brown wire coming from it (towards the car's harness).  What ever it is connected to disappears above the passenger side ventilation duct, near the in-car ventilator hose up there.  The other side of that connector appears to be a dark wire (I can't tell for sure what color it is on the other side of that connector), that's in line with the brown wire on the other side of the connector, and a yellow wire.  The yellow wire has no counterpart on the car's harness side of the connector (to go with the brown wire in the same connector).  I do have a yellow 16-18 gauge wire just hanging loose there. 

Does anyone know if this yellow wire is supposed to be in that connector with the single brown wire?  It's obvious people have been under the dash of the car before, so who knows what's good and not.  Thanks.

[Gene Beaird]

Well, I think I finally fixed it.  CadillacTim suggested a sensor 'open circuit' condition.  He was right! 

While out dorking around with the car some more, thinking to myself how I DIDN'T want to pull the upper dash off, since I cannot completely remove the lower dash due to ham-fisted POs directly-wiring a bunch of stuff in (stereo head unit and some aftermarket alarm sensor LED).   I played with the twilight sentinel (which I don't think works) and auto-dim (which is <yay>), I lifted up on the upper dash and discovered it loose.  I went around to the passenger side and completely lifted it up.  It seems there are _NO_ upper dash screws in the dash.  Anyway, I managed to move things around enough to look under it, and discovered the black and green wires for the in-car sensor just laying there, beside the sensor ventilator tube.  I connected all up, laid the upper dash back in place and fired things up.  This time, the air mix door lever did not go to full hot when I turned the key on.  The air mix door is now controllable by the temp dial as it should.

Time to bolt things back together, for now.  I do need to find out what screws are used to hold the upper dash to the cowl, as there are none in the car. 

Oh, and the green and black wires for the in-car temp sensor run up the center of the dash and then goes out to the sensor.  Just FYI, in case anyone needs to know.

[Althegut]

would the ambient temperature  sensors have any effect on the actuator doors/vents  other than temperature? thanks  guys  79 Seville