Td5 D2 Seats - Heating Elements

FRONT SEAT HEATING ELEMENTS. 

Pictured above is the heating element for a front seat 'squab' which is the upright back of the seat. Each front seat has two heating elements, one on the squab and another on the cushion. The white connector shown above simply plugs into the lead from the cushion element which itself then plugs into the fitted vehicle loom via the brown connector under the seat frame shown below.

All Discovery models have this brown connector under each front seat. It is wired into the vehicle loom and is used to supply power to the seat heating elements and the electric seat motors (if fitted).

Hx currently has black, fabric-covered, non-heated 

manual seats. It's electrical loom contains the wiring and connectors to enable the manual heated seat option to be easily installed.

Originally I was just going to install the 'manual' heated seat option and bought the above 'manual' element off E-bay. The plan has now changed to install fully electric seats and the above 'manual' element will no longer be suitable....

Although the heating pads for both the 'manual' and 'electric' seats are physically similar they do differ in their resistance and heating cycles and as a result of this they have differing part numbers ..

HGT500020   -  Seat cushion - Electric seat 

HGT500030   -  Seat squab - Electric seat

HGT500040   -  Seat cushion - Manual seat 

HGT500050   -  Seat squab - Manual seat   

These numbers are printed onto the element's fabric covering along with the word 'manual' or 'electric' to avoid confusion. It is important not to mix the heat pads together as that will lead to electrical inefficiencies and the potential of fire and burns!

Land Rover even issued a 'Technical Bulletin No 0130' back in 2004 that addressed this issue and the problem of local 'hot spots' on the seat cushion. ..

THE HEATING CYCLE. 

The operating temperatures are set by the factory and are not variable by the user. I believe that the lower target is 26°C and the upper target is 36°C.

Heated seat elements on an 'electric' seat are governed by a variable resistor/thermostat that automatically maintains or 'modulates' the heating output by varying the current draw as required in order to keep the operating temperature at the defined target.

The 'manual' heated seat is controlled by a simple thermostat that cuts power when the factory set 'max' temp value has been attained. When the lower 'min' temp is reached, the thermostat switches the power back on and the cycle repeats. 

I have read about the current draw being 150 watt which is a lot! The 'Owners Handbook' states that the heated seat option should only be used when the engine is running as the current is then supplied by the alternator. I don't know if that 150 watt figure is for both seats or just one. It also points to the need for the alternator charging circuits and the battery to be in a good healthy condition. I am now wondering what the rated output is for the fitted alternator?

CONSTRUCTION AND FITTING. 

Here are some close ups of the heating element sandwiched between the fabric layers. I photographed them back lit on a window to reveal their structure  

Any malfunction of the heating pads is nearly always due to breaks or creases in the thin wire element or in the connecting lead between the two elements on the seat. The wire is very thin and subject to a lifetime of flexing and compressing particularly on the drivers seat cushion.

There are many online accounts of repairs being undertaken to broken heating element wires by simply soldering and insulating the breakage. Most of the repairs can be done on the vehicle, but removing the seat is the preferred option as it allows greater access to remove the covers and foam pads.

The photo below shows the fitted position of an element on a squab cushion. It is attached to the foam cushion and lies beneath the outer covering. The method of fixing is just fabric glue, one side of the element is 'sticky-backed'. 

The connecting wire can be seen to be routed behind the base of the 'squab' foam. The seat 'cushion' is not shown. The cut-out sections on the element and the visible holes on the foam panel are to locate the 'hog-rings' that secure the covering to the cushion and the cushion to the seat frame.

Update  -  I keep meaning to uploadand insert the LR technical info sheets regarding faulty seat heat pads..  one day I will get around to figuring how to..!