Freelander 1 PTC Heater TD4

teddywood1 said:

thank you Jayridium yesterday i pulled the top off the relay and got the wife to turn ignition on and it worked i need to do a check if the voltage it getting through to the pct heater or rather the sone in law will as my back does not bend good .

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Nodge68 said:

Be aware that the PTC element will only gets power when the engine is running. I'm not sure where this originates, but from the CCU would be a good guess.

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Jayridium said:

@teddywood1
The system is set up using something of a dieing art - electromechanical engineering, nowadays most stuff like this is just programmed into a microcontroller, however this is done with sequential switches and relays, quite cute and quaint, but the specifics are:

• The first switch is in the dashboard, operated by a cam lobe on the heater control, when the temperature is moved to hot, 1 o'clock onwards, this sends power as the signal to the first relay (logic thusfar - occupants want more heat)
• The first relay, located in the cabin, receives its control signal from the switch in heater control, and on it's controlled side, opens an earth path for the signal side of second relay (logic thusfar - occupants want more heat enabling next relay which will check if engine running to power heater)
• That second relay, which is located on the bulkhead in the engine bay beside the ECU box ventilation corrugated tubes to the scuttle panel, gets its control signal live from the signal to the fuel pump relay. (when the switch is closed, the first relay is energised, and the earth path for this relay's coil is created). This second relay, once actuated/controlled links the 80amp fusable link to the 3x 30amp fuses (logic thusfar - occupant wants more heat AND engine running THEREFORE send power)
• After passing the logic tests above, ie occupants want more heat and the engine is running, the second relay is energised. The second relay supplies controls power from the battery, via the 80amp link, to the relay, then from the relay via a thick(er) single black wire that runs under the ECU and Fuseboxes in the engine bay, this then splices to three thinner wires under the engine fuse box, and they become the feeds for the aforementioned fusebox.
• Assuming normal PTC operation, ie: fuses reinstated, those three fuses then feed the three wires to the heater elements. Those wires, again, run under engine bay fusebox, going into the bulkhead, behind the dash and to the drivers side to feed the PTC elements.

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guineafowl21 said:

As you suggest, most likely to be corrosion in the fuse holder leading to poor connection leading to heat. I find either silicone spray or silicone grease helps avoid this.

The PDF does suggest three separate elements (labelled ‘3,2,3’ - mistake!) so you should run ok at 2/3 power. If it’s just one element, the fuses would have to be in series, which is unlikely, or parallel, in which case the two left will blow quickly.

You could either re-link the missing fuse with an inline car fuse carrier (ebay) or even get a scrap fusebox from a scrapyard, or online from 1stchoice.co.uk.

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Nodge68 said:

The PTC element is in the heater assembly, so the dash needs to come out, not the radiator.

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Jim Lloyd said:

Where is the ptc fuse box so I can check the condition of it please?

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