1989 Toyota Celica GTS A/C Heater Control Problem

I am on my second control unit in 2 years. The fan works fine, but
the heat turns on and off at its own will. I forced the water valve
open, but that doesn't fix it as I believe there is an air flap that
would need to be forced open. Does anyone know where I could find a
wiring diagram or know of a repair for this. Searching through
threads this seems to be a common problem. Thanks!

Vince
Calgary Alberta Canada

"vinnie" <vincekim@hotmail.com> wrote in message
news:1160690535.036647.308470@i42g2000cwa.googlegroups.com...[color=blue]
>I am on my second control unit in 2 years. The fan works fine, but
> the heat turns on and off at its own will. I forced the water valve
> open, but that doesn't fix it as I believe there is an air flap that
> would need to be forced open. Does anyone know where I could find a
> wiring diagram or know of a repair for this. Searching through
> threads this seems to be a common problem. Thanks!
>
> Vince
> Calgary Alberta Canada
>[/color]

I don't know if the 89 is similar to the 86 of not but in the 86 the systems
are worked by cables from the back of the unit. These are held in place with
dodgy little clips which I have seen break.
Did you change the first controll unit?
I would be doing two things I would pull the unit out of the dash to see if
any of the cables are are not conneced correctly and to pull on any that are
connected to the heater temp controll and see if that gives you constant
heat.
Secondly I would check to see if water is actually flowing through the
heater system. The tap could be broken internally or the pipes clogged,
after all no water flow no heat.

Nicholas

On the ''89 everything is controlled by solenoids so there are no
cables. I can see the water valve in the eng compartment and when the
control unit is acting up I can see it close the water valve and I can
hear flaps closing. I still have the original unit and there is a
slide type reostat that I think is the issue. If I can figure out the
wiring I may just jumper around it. I may have heat all the time, but
then I can always open the windows. It's getting pretty cool here at
night and in the mornings so I would prefer being a little warm to
freezing.


Nicholas Bourne wrote:[color=blue]
> "vinnie" <vincekim@hotmail.com> wrote in message
> news:1160690535.036647.308470@i42g2000cwa.googlegroups.com...[color=green]
> >I am on my second control unit in 2 years. The fan works fine, but
> > the heat turns on and off at its own will. I forced the water valve
> > open, but that doesn't fix it as I believe there is an air flap that
> > would need to be forced open. Does anyone know where I could find a
> > wiring diagram or know of a repair for this. Searching through
> > threads this seems to be a common problem. Thanks!
> >
> > Vince
> > Calgary Alberta Canada
> >[/color]
>
> I don't know if the 89 is similar to the 86 of not but in the 86 the systems
> are worked by cables from the back of the unit. These are held in place with
> dodgy little clips which I have seen break.
> Did you change the first controll unit?
> I would be doing two things I would pull the unit out of the dash to see if
> any of the cables are are not conneced correctly and to pull on any that are
> connected to the heater temp controll and see if that gives you constant
> heat.
> Secondly I would check to see if water is actually flowing through the
> heater system. The tap could be broken internally or the pipes clogged,
> after all no water flow no heat.
>
> Nicholas[/color]

vinnie wrote:[color=blue]
> On the ''89 everything is controlled by solenoids so there are no
> cables. I can see the water valve in the eng compartment and when the
> control unit is acting up I can see it close the water valve and I can
> hear flaps closing. I still have the original unit and there is a
> slide type reostat that I think is the issue. If I can figure out the
> wiring I may just jumper around it. I may have heat all the time, but
> then I can always open the windows. It's getting pretty cool here at
> night and in the mornings so I would prefer being a little warm to
> freezing.
>
>
> Nicholas Bourne wrote:[color=green]
> > "vinnie" <vincekim@hotmail.com> wrote in message
> > news:1160690535.036647.308470@i42g2000cwa.googlegroups.com...[color=darkred]
> > >I am on my second control unit in 2 years. The fan works fine, but
> > > the heat turns on and off at its own will. I forced the water valve
> > > open, but that doesn't fix it as I believe there is an air flap that
> > > would need to be forced open. Does anyone know where I could find a
> > > wiring diagram or know of a repair for this. Searching through
> > > threads this seems to be a common problem. Thanks!
> > >
> > > Vince
> > > Calgary Alberta Canada
> > >[/color]
> >
> > I don't know if the 89 is similar to the 86 of not but in the 86 the systems
> > are worked by cables from the back of the unit. These are held in place with
> > dodgy little clips which I have seen break.
> > Did you change the first controll unit?
> > I would be doing two things I would pull the unit out of the dash to see if
> > any of the cables are are not conneced correctly and to pull on any that are
> > connected to the heater temp controll and see if that gives you constant
> > heat.
> > Secondly I would check to see if water is actually flowing through the
> > heater system. The tap could be broken internally or the pipes clogged,
> > after all no water flow no heat.
> >
> > Nicholas[/color][/color]

Buy yourself a Chiltons manual from Amazon - covers most things, inc
full wiring diagrams, for the 88/89-93/94 models.

Vinnie, Did you ever find out what the problem is (was)? I am having
pretty much the same issue on an 87 Celica, it also has the cableless
control unit. I have had the radiator flushed twice within a week to
see if it was a clogged heater core. No change, I disconnected the
wire that controls the heater core bypass valve so it is always open.
I never could find the blend door so that remains an issue but I am
curious about what you found out with the electronic control assy. Did
it solve you problem initially?? Have you changed any of the heater
solenoids?
Thx,
Roy

"vinnie" wrote:[color=blue]
> I am on my second control unit in 2 years. The fan works
> fine, but
> the heat turns on and off at its own will. I forced the
> water valve
> open, but that doesn't fix it as I believe there is an air
> flap that
> would need to be forced open. Does anyone know where I could
> find a
> wiring diagram or know of a repair for this. Searching
> through
> threads this seems to be a common problem. Thanks!
>
> Vince
> Calgary Alberta Canada[/color]

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I’m having the same problem with my ’88 Celica - on and off operation
of heat regardless of control settings at high. I believe there’s a
vacuum assist to the system that could cause the problem. Has anyone
run into this?

"Roy" wrote:[color=blue]
> Vinnie, Did you ever find out what the problem is (was)? I am
> having pretty much the same issue on an 87 Celica, it also has
> the cableless control unit. I have had the radiator flushed
> twice within a week to see if it was a clogged heater core. No
> change, I disconnected the wire that controls the heater core
> bypass valve so it is always open. I never could find the
> blend door so that remains an issue but I am curious about
> what you found out with the electronic control assy. Did it
> solve you problem initially?? Have you changed any of the
> heater solenoids?
> Thx,
> Roy[/color]