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4.2 D4D "power Heater" - Info, Please


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Under the bonnet of my 2003 4.2, near the Battery, there sits "Engine Room Relay Box No.2", containing three HD relays, and three 50A fuses. I'd like to know exactly what these items control.

My UK owner's booklet refers to the unit on p.326 (Specifications & Fuses), as Fuses 42, 43 & 44, at 50A each, and labels them as Air Conditioning PTC1, 2 & 3.

None of this appears (well, I can't find it) in any of the Toyota engine, body or electrical wiring diagram manuals (that I have).

It's all fitted to Diesels Only (p.326 again), and my guess is that it's the "Power Heater (Electrical type)" that TSB BE-1009 (Apr.2001) refers to - or at least refers to in its Index, but with no further details!

What does it do? Well, with a cold diesel engine, and leaving home downhill for several miles, the engine (i.e. the cabin heater) takes just forever to heat up. BUT, if you simply turn the heater control to maximum, the last few degrees of turn accelerate cabin heating enormously . . . And by that I mean detectable heat within 60-90 seconds! So, are there three hefty electrical heating elements buried somewhere in the cabin heater circuit?

Mr T's workshop literature seems to keep this a guarded secret! Can anyone help?

Chris

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On later models with a diesel engine you have a PTC (positive temperature coefficient) heater. This is an electric radiator that sits in the air inlet and is operated in three stages depending on just how low the outside temp is and what the demand on the heater is. Because of the load, the stages are operated by the relays you have found.

It helps the heater come up to temp during the long warm up period on a diesel engine.

heater.pdf

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They often get much higher spec than we do and different colour interiors. Its down to TGB telling the factory what they want to sell. I think the person that does the interiors for the UK used to be an undertaker - black - black - black.

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Thanks Don, and everyone else, for the speedy answers. So, a PTC (positive temperature coefficient) device . . . These have a low resistance (and therefore high output) at low temperatures, and resistance and output drops as temperature climbs. Perfect! And, as it's warming the heater air intake, as opposed to the water, that explains its very quick response.

Just for the sake of it, I'll measure the current consumption in each of the three circuits, just to see what kind of additional load is involved. 3 x 50A fusing suggests quite a whack, and I wonder if it's ECU controlled to prevent cold-startup-idle heavy discharge. Will try to find out. Odd, though, that there's so little documentation and (seemingly) a complete lack of reference to the setup in either circuit diagrams or repair manuals.

Do we need it in Spain? Overnight this week is 7degC (17 daytime) 6km inland from Algarrobo, and 30km further north in the mountains February morning temperatures can be -8degC.

And yes, choice of trim and bits does seem all down to the importing country. We test-drove in the UK in 2003, and bought new in Spain immediately afterwards - and had to re-think all sorts of things like interior colour (grey here), body colour (anything you like, as long as it's Silver), and "Why would anyone want rubber mats???"

But the diesel is £1.11 (GBP) per litre!

Keep warm,

Chris

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Jedi - Thanks for the photo. No, I can't see the relay/fuse box in the pic. On my vehicle, it sits more or less just where your brake fluid reservoir is (mine's LHD). So perhaps it is market dependent.

Don - Your wattage figures are interesting... If the device was 50 or 60W, then a 5A fuse (or a bit bigger for margin) would suffice. This setup has 3 heavy-duty relays and 3 50A fuses. Assuming that a 50A fuse might possibly run at 30A actual load, then that'd be a total 90A load on the system . . . or 1080W . . . and that's pretty serious stuff for a 12v system . . . and approaching the total output for the alternator! All this is speculation, of course: I'll get an ammeter on the unit on a cold morning a.s.a.p. and see what's watt.

Chris

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How does the battery cope with this heater, I presume these are fitted to the 4.2 petrols also?

Do you know what amp rating your battery is?

Hi Jedi,

These heaters are fitted to DIESELS ONLY - and it appears not to all of them.

I'll measure the current drawn sometime during the next few days, and post the details. Will also come back to you on the rating of my Battery.

Chris

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Hi Jedi, Don

Herewith a shot of my engine bay, showing location of the Relay & Fuse Box for the boost heater.

Believe it or not, it's thundering and raining outside, so I'll leave current measuring 'til tomorrow.

Chris

PS Please ignore all the dusty brown stuff - it's "campo track dust".

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I have a little box like that, buts its Near the air box. When I get time I will open her up. And see what's inside.

Infact you can just see the top of it, to the right of the AC pipe in my pic.........It was not this one these looks like Fan relays Ac fans Maybe

So wait a minute you get electric heaters but no AC by the looks of it.? Maybe your rav was imported from colder climates?

What's the chassis number you don't have to give me if you don't want to. Pm it me :-)

Thanks for the pics

Have managed to quickly take some snaps...........Seems I do have these relays but they are mounted next to the Battery.........

Now I not sure my booster heating system is working, as I dont really notice any rapid heating up of interior.............Or maybe I`ve been spoilt and expect more from them?

Is there any way to test whether these are working, are they accesable from the inside of the car some how? Pollen filter area maybe?

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post-73910-0-03346200-1327673697_thumb.j

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What does it do? Well, with a cold diesel engine, and leaving home downhill for several miles, the engine (i.e. the cabin heater) takes just forever to heat up. BUT, if you simply turn the heater control to maximum, the last few degrees of turn accelerate cabin heating enormously . . . And by that I mean detectable heat within 60-90 seconds! So, are there three hefty electrical heating elements buried somewhere in the cabin heater circuit?

Mr T's workshop literature seems to keep this a guarded secret! Can anyone help?

Chris

Mines got Climate control with buttons not the dials you have? Do I wack the temp up to max inorder to engage boost heating :D In fact its got a !Removed! load of button!!!!! Im pretty sure I know what they all do, but do they have hidden functions? when wacked up to the max?

Will anything be said in the manual....I dont think ive actually read it. :dots:

post-73910-0-74429300-1327676922_thumb.j

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Hi Jedi,

The Fuse/Relay Box you show in your photos is identical to mine (PTC1,2,3 and 3 x 50A fuses), and is simply located on the opposite side of the vehicle, yours being RHD, mine LHD.

My vehicle has AC, but is 3 rotary dials - yours is obviously digital climate control.

There is absolutely nothing in my Owner's Manual about this "electric heating boost". It's just not mentioned. And it sounds as if your Owner's Manual (covering the Climate Control version), also doesn't cover it. My guess is that Mr.T decided not to go into details for the owners, but simply allow them - in all reasonable expectation and blissful ignorance - to get more heat out of their cabin heating systems by simply turning the heat control up to maximum! Do please have a look in your Owner's Manual.

I have a knob that does this (no comments, please) in the last few degrees of turn. It's anyone's guess what you need to do with a digital system to boot it into operation. Presumably a good Toyota engineer / Toyota Technical would know.

Curious, as I've remarked before, that no circuit diagram I can find seems to show this device or its connection into the power source. Don . . . Do we have any TSBs or updates or supplements covering this?

The facility is a good one: cold engine, frosty morning, misty/icy windscreen, and only the prospect (if you're unlucky) of a downhill run to start your journey. By simply setting the heater to max, you get warm air within a minute or so, which you'd never achieve otherwise.

I also have no information about where the (three?) PTC heating elements are actually located. My guess is that they would perform best when positioned in the heater airflow, after the water matrix. Unheated water in the matrix would leave the PTC elements in a cold airstream, their resistance would therefore be low, and their heat output high. As the matrix rose in temperature, their resistance would increase, thus decreasing the electrical current flow. (PTCs can be design-specified to have a maximum operating temperature. As this is approached, their resistance climbs sharply, reducing their output. Clever stuff!) . . . But, this is all just a guess.

Chris

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Whats does PTC stand for? are you refering to the electric heating element or elements...........similar to that in a hair dryer toaster?

Never mind found it in Dons previous post...............

Nice bit of kit..............its not stone age after all :blow:

http://www.beru.com/...bin-heaters-ptc

Looking at that I should feel the heat really.................Hmmmmmm pretty sure mines not working or........Im not engaging it.....................will have to dig out maunal and see if it says anything in there?

Mine definatly does not defrost the windscreen in seconds as mentioned in the link,

Hmmm I wonder if it can be accesed via diags? Mentioned in the link again.

Unless Dons got some PDF`s :)

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Hi Jedi,

You're right - not quite Stone Age, it seems.

Don't let me mislead you about how good/quick the facility is. On a cold morning (5-10degC) if the engine is started, and then the heater (rotary) control is set to maximum, with the blower fan on Low-Med, there is feelable warmth after about 60-90 seconds. After about 3 minutes, it would begin to shift windscreen condensation - and/or stop your fingertips dropping off.

By the way, my chassis is J T E H G 20V 6000 43744, if you want to explore further. Let me know if it's Siberian or Icelandic!

Best regards,

Chris

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Seems it is specified for Spain, Coutry code=ES Not sure how acurate this software is, but its pretty spot on with mine.

I just thought you didnt have any sort of aircon.....which got me thinking why not in a hot climate???

Does say in spec list you have the LSD in rear diff though............ :D

JtheG20V600043744.pdf

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Hi Jedi,

First, thanks for obtaining and posting the production details of my 4.2 – it all looks pretty well spot-on.

Well, it’s finally stopped raining, and the 12-hour thunderstorm has also gone, and so I ventured outside this morning...

Power Heater, Electrical

Outside air and vehicle temperature was 9degC, after standing overnight. I pulled all three of the 50A PTC fuses, and inserted an ammeter into the first fuse position. Started engine, and set temperature rotary control to maximum. No initial reading on meter, but after about 10 secs meter pinged to a 35A discharge for about 1 sec, and then dropped to a steady 20A, where it remained.

Repeated with the other two fuse locations, which both did exactly the same, except that the cut-in delay varied between circuits, max being about 35 secs.

3 x 20A = 60A = 720W at 12v, or 840W at 14v. Quite a load.

Although the three relay circuits operate “simultaneously”, I can only guess that the cut-in time delay varies between circuits to prevent a nasty sudden 105A surge of all three switching on together, and this at a time (cold start) when alternator load is already very high. Just a guess. And the 50A fusing is to allow for the initial 35A load.

What I haven’t done is to see how the 20A might reduce as things warm up, or cut out (or not operate at all) at normal working temperatures.

(If anyone wants to do their own checking, then it’s easy to connect an ammeter into the PTC fuse locations: Remove fuse, and terminate your meter leads with standard 0.25” female spade connectors, making sure you leave a small gap between them!)

Chris

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Thats some currect drain 60A and peaking at 105A , Wonder what its like when you`ve got the lights on the heated seats etc. :help: There must be some hefty cables going to this PTC.....

I wonder if the ECU`s stagger when everything powers up? I imagine they must do....

I wonder how long does this heater stays on for? Untill engine warms up I presume?

My Fluke meter only has a 10A DC current rating, not much I can do with that :huh: I supose thats one way of testing the PTC if its drawing a current it must be working?

It must come as part of:

87107A / 87107-42140 UNIT SUB-ASSY, HEATER RADIATOR

87107A: for the Diesel engine,, you can see the extra part in the diagram, this must be the PTC

87107: for the petrol engine, without extra part.

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Hi Jedi,

Well, thanks for this. It's the first time I've seen any diagrammatic reference to the PTC. Well done, my friend!

My Toyota Repair Manual is RM777E (May 2000), and this only shows the standard heater radiator (87107 in your diagram). Don did suggest that the PTC facility appeared later on, so perhaps that's why my manual doesn't cover it. And neither does my Toyota EWD416F (May 2000) wiring diagram manual. (I bought all these manuals in early 2004, and they were then the latest available.) Which publication did you find your heater parts diagram in? And is there a wiring diagram detail as well?

So far as current consumption goes, you've come to the same question I did originally: what (if anything) might all this current drain be doing to upset other things?

My interest in the PTC was originally triggered by several folk complaining of poor cold starting, and I've had this myself the winter before last when the Battery seemed able to turn the starter ok, but the engine just didn't want to fire up. I got sidetracked onto all sorts . . . glowplugs, fuel filter, fuel delivery pump, etc etc. Turned out that all it needed was a new Battery (after 7 years!).

But one obvious scenario to avoid, I guess, is to get into a very cold car, and unthinkingly to wind the heater up to maximum, and then to try to start it! This would be made even worse if you'd also put the headlights etc. on too. So the moral seems to be, now we know the device is there, be wise enough to activate it only after you've got the engine running.

My Fluke-alike only goes to 10A too, so I had to dig out a 1960s-vintage Smiths dash ammeter, and use that. What I will do during the week is hook it back in, and see what happens to the current when the system warms up, and also check what happens when you do a restart at full working temperature.

Chris

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