Discovery 1 300tdi - no heater blower

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paul williams
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Discovery 1 300tdi - no heater blower

Post by paul williams » Tue Feb 19, 2013 3:19 pm

Why do things always happen at the wrongtime, somebody's law no doubt. During the recent snow I decided to give the Disco a spin, it had not been used for a few weeks as I was enjoyihg driving around in the 600. With the snow I thought the disco might be a better option. For the past few years the Discovery ( 1995 300tdi ES) has been reliable so I wasnt expecting any problems. It started fine but during a brief drive the heater blower stopped. This had happened a few times before when the fan was on the fastest setting (4) and normally a quick reset to postion (1) on the slider control and then back to (4) and all was well. Not this time. Coincidentally during the same trip my daughter complained about water dripping on her feet while sitting in the passenger compartment.

Upon investigation, when the heater slider control was moved from (0) to (1) there was a clicking from a relay behind the glovebox on the passenger side. I investgated further and found that the passenger footwell was very wet, so wet that slight pressure on the mat, on the carpet produced water seeping out all over the door tread. I removed the trim from the passenger footwell, removed the carpet and also the moulded rubber sound deadening. This is basically a rubber cover bonded to about 1 cm of foam which makes a very good sponge. The moulding went over the transmission tunnel and appeared to be in one piece but I was able to make a cut, just below the trim on the tunnel to allow me to remove only the passenger side. This and the carpet were put out to dry and the floor mopped up. There were lots of signs of rust on the floor I dont know at this time if the floor is perforated thats another day.

I located where the relays were, on a hinged panel behind the glovebox where they were very wet, the relays just clip on this frame so I removed them all and let them hang loose. By operating the heater switch the clicking noise was indentified as coming from a larger relay covered with its own rubber shroud.

Image

The print on the shroud identified it as:

Denso 058700-3300 with five pins, arranged in two rows.

I opened the relay up, taking off the rubber cover and the plastic case and it was FULL of black slimy water and metal dust, a bit like wet iron filings, one contact had completely disintegrated.

I went to my local LR dealer to get a replacement, which they had in stock for £55.00 :o , I refused this as I was sure there must be another way to sort it out.

The relevent bit of the circuit.( Note how the changeover works, earthing the blower when off, also the connection numbers)
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I looked at the circuit diagram for the blower and noticed it was a simple changeover or SPDT (single pole double throw) relay. By connecting together the wire from the heater to the feed from the fuse box, the blower came back to life, so hopefully a new relay was all that was needed.

Looking at the pin connections on the relay it seemed a little odd, there were two heavy duty connections and a smaller one, (ignoring the coil connections), it wasnt a standard chageover relay as then it would have equally rated contacts. Re-examining the circuit it showed the heavy duty contacts were used to connect the blower to the supply and the smaller connection was to connect the blower to ground. I am not sure why this is needed unless it is to provide a back emf to brake the blower fan when switched off. It did however show that a normal relay could be used instead.

I needed to know the rating of the relay so I bridged the blower and feed connections with a multimeter set to 10amps DC, the reading was 9.04A on fast(4). So a relay rated at 10A or more would do.

Note the other relays hanging down, and the rusty floor!
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An ebay search found a suitable standard relay with connector and pins for less then £3.00 including postage. So all that had to be done was work out the connections.

Relay and base and connectors from ebay
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For those who are interested the following are the connections required.

The original relay worked as follows:

Relay on (energised - fan on) positions (2 - 4)
Image

The colours are the wire colours from the wiring loom and the numbers refer to the numbers on the circuit diagram.

Relay off (de-energised - fan off) position (0)
Image

Wiring of replacement relay to do the same thing.

Note the numbers, 85,86 which are the coil and 30,87,87A which refer to the changeover switch and are also referenced on the circuit diagram within the relay enclosure shown on the diagram, the wires now have to transferred across.

Image

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Next post:

Making the connections and finding the leak :?

Paul Williams
1929 2litre Saloon
1947 P2 16HP
1951 Rover Cyclops
1974 P6 3500
1998 LR Discovery I
2002 75


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47p2
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Location: Glasgow
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Re: Discovery 1 300tdi - no heater blower

Post by 47p2 » Tue Feb 19, 2013 7:43 pm

Interesting read Paul, I tend to forget that we also cater for modern vehicles here

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lakesrally
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Location: Lake District, UK
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Re: Discovery 1 300tdi - no heater blower

Post by lakesrally » Wed Feb 20, 2013 1:08 am

Good work Paul. Best of luck with the leak though, I had a leak in my previous Disco, which was similar to yours, a few years ago, it was coming from the heater matrix.

Regards

Stewart
Stewart Devlin
1925 16/50 5-seat Tourer
1933 14 Pilot Saloon
1949 P3 75 Saloon

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paul williams
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Location: Telford,Shropshire
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Re: Discovery 1 300tdi - no heater blower

Post by paul williams » Sat Feb 23, 2013 9:17 pm

Just to finish off..

.. having sorted out the connections it was time to put the new relay in. I used the following tools:

Image

Although the connections can be crimped I prefer to solder them. I find the soldering gun the best for car electrics, especially working outside. It provides instant heat hot enough to solder most wires and connectors and has the benefit of cooling down quickly so you can put it down quickly. It works much better than a traditional iron which can be fiddly and underpowered. The solder is original lead solder with a flux core as used by plumbers. The side cutters for clipping and baring the wires.



Image

This picture shows ( not very well) the new connectors soldered onto the wires clipped off the old relay base. When all are done the new connectors push into the new base and click securely into place.

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The finished relay and base connected and all is well, I now have a heater again working on all speeds and the previous intermittency seems to have disappeared so it was probably the old relay arcing over. Instead of £55 I spent about £4 plus a couple of hours and now have the advantage of being able to swop out to a standard relay in case of future problems.

Now for the leak, I dont think it is the matrix as the water doesnt smell of antifreeze and the system has not lost any water.

Paul Williams
1929 2litre Saloon
1947 P2 16HP
1951 Rover Cyclops
1974 P6 3500
1998 LR Discovery I
2002 75


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