No heat... heater core coolant valve perma-closed.

[GrimJack]

While I'm not entirely stumped... yet... the options I'm left with are all rather... distasteful.

So, here's the story. The vacuum operated valve that allows hot coolant into the heater core doesn't open under normal operation.

The valve is fine - if I bypass the VSV and feed it straight vacuum, it opens normally.

The VSV is fine as well. Swapped with a known good unit, same behavior. It's just not getting any signal to tell it to open.

I'm not entirely positive which coolant temp sensor this is dependent on, however, most of my sensors are brand new from Toyota anyway.

What I haven't checked:
- Wiring continuity. It's possible that I have a short / break somewhere in the wiring. Not entirely likely, as I rebuilt the engine wiring harness a few years back, but I won't rule this out.
- Circuit breaker. The TSRM mentions a circuit breaker in the AC section. It doesn't, however, mention *where* this is. I'm sure I'll find it eventually... passenger side kick panel, perhaps?
- The climate control unit itself.

Anything obvious that I might have missed?

Any tips for what affects this VSV would be appreciated as well.

Admittedly, I could just leave the VSV out of the equation, or bypass the valve entirely, and it will work fine. However, I'm a little bit picky about the details, and I like everything to work the way it was designed, so I'll be a fair bit happier if I can figure this out.

 

[dumbo]

Does your fan work? Mine comes and goes, so if you can find the circuit breaker PLEASE inform us/me!!, I believe, IIRC it is a TYPE II, resets automatically. But I couldn't find it. Maybe jetjock can enlighten us

Do you have system volatage at the 2 wire plug to the solenoid to the heater VSV? And since your certain you have continuity in the coil, I won't ask. If you don't have the 12+volts there, time to chase wires I guess, or the AC amplifier?


Just so you know, I bought a good VSV, tested good, forget the OHMS sorry, put it on didn't work, tested it again, OL. There old, test it.

 

[92TealSupra]

Well, your water VSV has two wires, one Solid Yellow, the other Black with a yellow Stripe going through it.

The yellow goes to your M1 Plug, and your Black/Yellow goes tot he b1 plug [ Big square Plug ]

If you want to check those to see if they're connecting that is where you looking, the m1 plug has the following colors.

M1 Plug
Black
Yellow/Red
Yellow
Red/Blue
Purple
Yellow/Green
Gray/Green
yellow/Black
Brown


Hope this helps!

Edit; The yellow is ALSO Plus for backup light switch Plus for A/C water valve VSV - Yellow
Plus for A/C water valve VSV

 

[Nick M]

I was going to suggest probing the plug and turning the heat to 85 and see if the signal is put out.

Take a look at the pins. Sometimes they get messed up, just a tiny bit, and loose continuity. Not that the unit is easy to pull.

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=142

I haven't had to deal with a failed VSV yet on my heater.

 

[IJ.]

Possible dead amp in the CC unit.

 

[nytefire]

Edit: 92TealSupra: I see what you're talking about for the M1 and B1 plugs. I'll look at tapping the B1 side and go from there. Thanks.

I'm running into the same sort of thing, but I know where my problem is. My wires were cut to the VSV. I was planning on routing new wires into the car, but I for the life of me cannot figure out where to splice into for the "A/C" AIR MIX CONTROL SERVO MOTOR" I know its off pin 4, but it doesn't look like it goes into the plugs that service the a/c controls, which are "D" and "E".

I have a 1j swap, and my harness doesn't go into the stock 7m harness spot through the firewall. Also I have an 88 body if that makes any difference.

I know I can run a line from J/B #3 for the solid yellow, but I'm at a loss where I can find the Black Yellow line.

(not meaning to hi-jack your thread, but I didn't want to post for nearly the same issue)

 

[jetjock]

That's a pretty simple circuit as far as the climate control system goes. You should have +12 (from the gage fuse) on the yellow wire to the VSV when the key is on. The ground (yellow/blk) is supplied by a set of sliding contacts in the air mix servo and originates at ground point D which is the set bolt for JB #1. This ground is always provided to the VSV connector unless the air mix damper is driven fully closed (control head set below 66 degrees).

I'd first check to see if you have 12 volts (reference the chassis when doing it) at the VSV connector with the key on. Then switch to ohms and, again referencing the chassis, see if ground is present. That way you can find out which side the problem is on and cut your diagnostic work by 50%. I suspect the ground side will be missing. If so check that the mix damper is moving by putting the system in auto and running the temp set point up/down and going from there. Lastly, neither the CB or AC amp can be involved...


Edit for dumbo: The 40 amp heater CB that runs the blower is in the right kick panel:

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=22

Been years since I've been in there but I'm 99% sure it's the manual reset type. The others are...

 

[IJ.]

Thanks for the correction I had a no heat issue that was amp related but that was a mixer door issue and not the vsv, wasn't sure if it was on the same control circuit.

 

[jetjock]

It wasn't meant to be a correction Ian. I was talking about the AC amplifier while I think you were talking about something else. If not then it was a correction. Then again since it's not possible for the AC amplifier to effect any of the servos/dampers (unless it's an OZ car thing) I dunno where we go from here

 

[tekdeus]

I think I have a spare 87-88 climate control you can have to try out Dave. But yeah, check that the solenoid clicks open with 12v, and then check to see if those 2 wires are getting 12v when on hot.

 

[dumbo]

Thanks jetjock! Why didn't I think of looking in the manual haha. I'll check her out. The hunt continues.


Any updates?

 

[GrimJack]

That's a pretty simple circuit as far as the climate control system goes. You should have +12 (from the gage fuse) on the yellow wire to the VSV when the key is on. The ground (yellow/blk) is supplied by a set of sliding contacts in the air mix servo and originates at ground point D which is the set bolt for JB #1. This ground is always provided to the VSV connector unless the air mix damper is driven fully closed (control head set below 66 degrees).

I'd first check to see if you have 12 volts (reference the chassis when doing it) at the VSV connector with the key on. Then switch to ohms and, again referencing the chassis, see if ground is present. That way you can find out which side the problem is on and cut your diagnostic work by 50%. I suspect the ground side will be missing. If so check that the mix damper is moving by putting the system in auto and running the temp set point up/down and going from there. Lastly, neither the CB or AC amp can be involved...


Edit for dumbo: The 40 amp heater CB that runs the blower is in the right kick panel:

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=22

Been years since I've been in there but I'm 99% sure it's the manual reset type. The others are...

So, yellow wire has 12v. Ground wire has continuity to... nothing. JJ scores again. The mix damper... as long as I'm looking at what I think I should be looking at, it's moving. Slides around quite a bit when I go from anything to full cold.

So, at a guess I need to find whether it's actually providing continuity to ground when on full cold.

The little bastard isn't the easiest part to get to, either!

 

[jetjock]

Yeah, it's a bugger to get at. If you can try checking for ground on pin 12 going in and pin 4 going out. That'll at least tell you whether it's really the culprit. You're looking for ground when not full cold btw. Remember, anything above full cold energizes the VSV to open the coolant valve. It's why when the usual failure occurs (the VSV itself goes tango uniform) there isn't heat.

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=142

Here's hoping it's OK because the price of that thing is not for the faint of wallet. The usual servo failure mode occurs when the pot develops a flat spot and the damper chatters from the intermittent loss of feedback. Not your problem though...

 

[GrimJack]

Update!

Luckily I spent 15 years in Eastern China learning to become a contortionist, because that's what it takes to be able to test pins 4 and 12 on that connector without removing most of the cabin.

I get a consistent ground on 12, and ground on 4 when it's not on full cold.

On the one hand, I was really hoping this was the culprit, because expensive or not, I thought replacing this part was going to be a crapload easier than chasing wires. Now that I've spent a bunch of time trying to get at this little cretin, I'm not so sure I still think that way.

So, now I guess I'm left with trying to find a break or short in this wire between where it leaves the mix damper and where it gets to the VSV... or stringing a new wire if I'm willing to take the hack method.

Any other connection points / junction boxes / pink unicorns that you're aware of that might be the failure point? I realize that I'm asking for the automotive equivalent of that pony I wanted when I was 6 years old, so apologies in advance.

 

[jetjock]

Then the break has to be between there and the VSV connector in either the wire itself or the two connectors downstream. First make sure you're dealing with the right servo. Are the wire colors right? Pin 12 white/blk and pin 4 blk/yel? Does the ground on pin 4 disappear when the CC head is set to full cold? If so the next step is to check for ground at connector K1 (pin 10) or, if you're feeling lucky, connector B1 (pin 1). K1 is is near the servo (it'll be white) and B1 (it''ll be gray) is near the ECU/firewall:

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=28

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=29

To keep yourself honest when checking these remember the wire color on both connector's pins should be blk/yellow. Test for ground by either working forward from connector K1 or backwards from connector B1. My technique is to go directly to whatever point is easiest to access in the hope I'll get lucky. For example in this case if B1 was easiest to get at I'd go there first. If you find ground at B1 you'll know the problem is further down the line, if not you'll have to go backwards to connector K1. It's a crap shoot but doing this will often save you from digging into a tight place only to end up finding the circuit is OK there.

Check using whatever technique is best suited for the situation: voltage, ohm to the chassis, or ohm point to point. If there's any question about a wire positively ID it using continuity. For example if B1 pin 1 isn't blk/yel disconnect B1 and ohm from the VSV connector to B1 until the wire is identified. You can do that by either extending the meter leads or, easier, shorting the wire to be checked (the blk/yel wire at the VSV connector in this case) to the chassis and using the chassis as the extended meter lead. The point is any time you're doing this sort of troubleshooting you must be careful not to get led astray. If anything doesn't seem to jive with the schematic stop right there and resolve the mystery before continuing.

Finally, gently shake/twist the harness and cycle the connectors even if they check out. It's been a long time since they've been apart and cycling them can prevent future gremlins. In fact doing that first may resolve your problem.

Giddyup

 

[GrimJack]

Thanks for all the help, JJ.

The wire colors check out, as does the ground disappearing from pin 4 when I set the climate control to full cold. The bit about the right servo is definitely justified though, because the first connector I pulled apart turned out to be the wrong one! The correct one was only an inch or so away, but it was even harder to get at, of course.

I've got a can of this electrical connector cleaner that I seem to recall was suggested by you a while back, I always pull the connectors and clean them when I'm there just as a matter of course. An ounce of prevention, as they say...

If I'm lucky I'll find a popped / bent pin in one of the connectors... if not, I guess I'll have to pull and separate a wiring harness so I can re-string that wire.

 

[jetjock]

Good luck with it Dave. It's nice to know there are people in this community who're still willing to do things right even though it takes considerable effort at times.