Unusual Cabin Heating Failure

[twopenceworth]

Hello Forum members,

 I'm new to this site.

 I very much hope that with your help and feedback I can resolve a problem relating to my Corolla's heating system, or at least reduce the costs to fix it. I have trawled through many previous posts on this site referring to Corolla heating issues to try to resolve, but my vehicles fault symptoms are quite different from those I have read about. I have a bit of expertise (I like to think!) but I have little knowledge of the Toyota climate control system.

 

Car Details: 

Vehicle: Corolla Hatchback, 2006, Auto, Climate Control, 19400 miles. Car purchased 13th April, 2015 at 10 K miles.

 

Fault Symptoms:

• In the summer, and with the heater set to cold, engine just arrived at full temperature, the heater dispenses a huge amount of heat. The heater reverts to cold after 10 - 15 minutes, and stays (correctly) at cold. The cycle again repeats when the engine is turned off, allowed to completely cool, and is then restarted.

 

• Following an overnight soak below freezing, and the cabin temperature display set to 20 degrees. Engine started, and full temperature reached, but no heat is supplied to the cabin. The heater is sometimes persuaded to operate by turning the engine off and then restarting it. An alternative route is to raise the displayed temperature above 27 degrees. I am guessing, but the blown heat supplied does not seem to reflect the temperature displayed on the dash. The velocity of blown air via the fan through all the heater mode options is very good, and it functions correctly.

 

Status Of Various Elements:

 

The cabin filter element is new and installed correctly.

The coolant is filled to the maximum level in the expansion reservoir and is clean and pink. The cars mileage is extremely low, so an issue with the heater matrix is unlikely.

The engine thermostat might be aged and less efficient, but the heaters entry and exit pipes are untouchably hot with the engine at full temperature.

 

Any feedback would be very much appreciated from other members, I suspect, but clearly do not know for sure, that an electronic component has failed, the question is which and where?

Kind regards.

 

[RazzerRazor]

Hiya pal. 

I'd find somebody near you with the same car and swap afew parts to see if anything works before spending (maybe on here and ask who's local to you to help you out). Or find a scrapper and go down that route. 2nd hand Rolla parts are quite cheap now days 

[twopenceworth]

Hi Razzarazor,

Yes, one route I propose to go down. I thought it shrewd if I asked fellow forum members, like yourself first. I live  25 miles from the nearest breakers, and an email to them has had no response. I will make a visit.  I am OK at vehicle maintenance, providing I understand the mechanics, operation and control system of an item, but the Corolla Haynes manual only gives data for the 'rolla manual heating system option, and nothing re the alternative climate control fitted to later vehicles. I can hear what I think may be a servo motor cycling in a repetitive but uncontrolled way, so I also need to remove a few covers. I have two identical spec' 'rolla's the same age so can compare. I am out of my comfort zone fiddling with electronic stuff, but I am happy to change complete units.

I have owned many vehicles over the years, but I am hugely impressed with the dynamic little Corolla. It scoots around bends with barely a concern, but I would appreciate a more torquey power unit for hauling my trailer - the side effect of 16 valves and lower emissions.

 

Best Twopenceworth

 

[oldcodger]

Hi,

You do not mention which engine you have ?

There seems little clear info on the digital heating / cooling system, have not been able to find if the hot water pipe is physically turned off via a valve or the heat controlled just by the flaps.

You should only hear the flaps servo when you change temperature , say changing from 25 to 23 will produce a servo sound for about 1 second, then stop ,( depending on the cabin  temperature)  until the next change by you or (assuming) its own controller tells it to adjust the flap to maintain the correct temp..?

The fact yours is moving all the time could be a broken linkage ( easily viewable from looking under the footwell) or perhaps a faulty temp sensor or control unit, but how and where to check them..?

[twopenceworth]

Hi OC, 

Your comments are sharp and helpful, I am appreciative of your feedback as I am also of Razzarazors. My engine is a 1.6 litre unit and the car is a colour code model, 2006 year.

Yes, I have done searches both on TOC and online to grasp how temperature is controlled on the climate control system but without success. Is the temp air flap movement calibrated direct to the digital temp display or via a thermostatically controlled sensor? My guess is that it is the latter, as the temp display is in half degree increments and a crude air flap control would have difficulty to respond to that degree of precision by direct control from a servo motor alone.

I go along with your argument - a failed or broken control linkage sounds extremely plausible. The way I approach stuff like this is to do my homework first, so I have not dismantled anything yet. One curiosity is that the  cycling servo sound I believe I have heard is intermittant and does not occur every time I drive the vehicle. However, a local independant garage certainly heard it last week and commented that they thought it a servo control motor. 

I would be a happy rabbit if I could aquire a diagram showing the layout and components of the system. A wiring diagram in addition would be magic!

Thankyou for your thoughts,

 

best

 

Twopenceworth

[oldcodger]

Hi,

You can see one of the servosand its gear /linkage on the side of the unit from the footwell without any dismantling, just do not blame me is you dislocate your neck  !

Below is a 2004 service sheet , may be an US model ?  but might give you something to go by.

Can only see reference to the Cooler thermistor, so does that controls everything ??

Perhaps a look at the back of the digital display panel might reveal another thermistor ??

Again, apart from those Damper flaps, what controls the hot water flow ??

As for servo noise, you do get such a noise at ignition on as the headlight beam servos operate.

_Wiring Manual.pdf

55 - HVAC.pdf

[RazzerRazor]

Not sure where you live but I'm in the north west, if you want to pop up sometime I'll take my console out and try it in yours and vice versa! 

[twopenceworth]

Hello All,

You have been most helpful.

A couple of things that I am clearly guessing at: 

I suspect that there is no valve to control the water supply to the matrix from the engine, but that excess heat from the matrix to the cabin is vented to atmostsphere via the heater air flap control. Heater water valve operating loads tend to go up as they age, and with the plumbing they can be bulky, so not technically popular. I have not found a vent to atmostsphere yet, perhaps it is a short element of the lourvres below the windscreen, but that would conflict with forward air pressure. The cabin temperature I think is monitored by a thermister (electronic thermometer) which electronically controls the air flap in conjuction with the temperature called for from the dash digital display. Whether it is this same thermister that also controls the a/c or that the a/c has a secondary unit I can only surmise.

Thank you for the kind offer razorrazor, but frustratingly I live in West Sussex- so a good way from you. With all of your help I will get this sorted!

Best to you all, for Christmas

 

Twopenceworth

[oldcodger]

Would be interested to hear if you find out those answers, seems our Digital model is not well covered, info wise.

That said they generally seem very reliable apart from quiet a few folk with 2001-2004 models having the heater matrix block up, plenty of posts in this forum about that, but never read anything about a control valve or thermistor.

 

And the poochs name is....?

[twopenceworth]

Hi OC,

I will update you all as I progress this. I, like yourself am surprised at the dearth of info on this particular heating system. 

At the expense of sidetracking you, my old friends name is "Ochre", we lost him in April this year at age 13, my family and I miss him a good bit. He was a tall and handsome guy, with a gentle disposition. We have a new 9 month pup, Onyx, who I am training to be a gundog, his dad is a national champion, and his mum competes locally.

Best,

Twopenceworth

[oldcodger]

Hi,

Unable to find anything specifically on our digital controls but did find these links which might make things a little clearer.

Begin to wonder if  our style of digital control were only fitted to our late Uk models, hence so little out there.

http://www.tcorolla.net/components-1266.html

and from p89 on -

http://www.autoshop101.com/forms/ToyEWB.pdf

 

Yes, Labs and GR always such good temperaments.

[twopenceworth]

Hi OC,

Again, thank you, I assure you all the info you send is carefully read and much appreciated. 

My daughter bought an 02 Corolla,when it was almost new, and that had a climate control heating and a/c system fitted, so I think it was always available, but probably for the top end models at that time. It was my first introduction to the car, and I was really impressed with its build quality and relative simplicity. The chain cam completed my enthusiasm, combined with the Honestjohn.co.uk recommendation and review  Like most Corolla's of that period it began to use oil, so it was sold on.

You might be interested in the attached link, which I have had for some time, but gives an insight into automotive oils evolution. What intrigues me about the current oil viscosity's recommended by Toyota for their cars are their low values, most likely for lower emission/lower fuel consumption philosophy rather than for best engineering practice. A viscosity of 20 works of course, but I would want to use a more expensive synthetic product with PAO formulated into it, especially for summer use.

https://www.volvoclub.org.uk/engine_oil_history.shtml

 

Best,

Twopenceworth

[RazzerRazor]

No worries pal. That's what we're all here for! Many hands and heads n all that ha ha