Condenser fan not running at cold idle with AC engaged. Is the condenser fan thermostat/sensor controller or should it always be running when the AC is engaged? Maybe this is my problem?

 

Went out to my 2000 Disco parked since yesterday. Turned it on at 80F ambient, AC on idle; the electric fan was turning slow from the suction of the belt driven fan, not electrically energized.

 

OK, looks like a condenser fan issue that is causing the overheat. Going to start a new thread, but in case anyone knows about this circuit/system, I am going to reproduce my diagnosis so far here.

Tested voltage on both sides of the 100A fuse that is supposedly for the condenser fan (F4 in the fuse box in the engine compartment) and got 12.7v with engine off and 13.8 with engine running.

Pulled relay (R4 n the fuse box in the engine compartment). See pics below.

Though not the typical 85-87 diagram, it appears that pins 1-2 are the energizer/control and pins 3-5 are the power.

Tested voltage and resistance at the blades/pins

Pin 1: AC off: 0V AC on: 13.7V open
Pin 2: AC off: 0V AC on: 5.7V open
Pin3: AC off: 0V AC on: 0V 14ohms
Pin5: AC off: 0V AC on: 0V open

Based on this it appears that the energizer circuit has voltage-current -- albeit the 5.7v when the was AC on seems weird. There is no voltage-current on either pin 3 or 5 of the power circuit, though the 14ohms on pin 3 seems consistent with what would be expected for the windings on a motor.

I am going to test the condenser motor here next by putting 12v DC on pin 3 and see if it spins (normally, I would do it at the motor connector itself, but I have that foam-ish OEM grill guard, which makes it a pain to remove the grill to get to the condenser fan motor connector).

As there was voltage on both sides of the fuse, I assume that the fuse is before and not after the relay on the power circuit?

Does this mean I have an open circuit somewhere in the fuse box between the fuse and pin 5 the relay? I am guessing there is a wiring harness/backplane on the underside of the engine compartment fuse box, perhaps with a bus bar or similar that provide 12v for the power circuits for the relays?

Am I on the right track here?

Does anyone have any advice?

 

Never had a problem with an AC condenser fan so can't offer any experienced advice there although it looks like you are on the right path to getting the electrical traced out. I usually just go to the fuse box and check at the relay/jumper it.

As far as the thermostat temp, 170 will not throw a code in summer but will in the winter.

For others benefit regarding how thermostats work, there is a special wax in the thermostat that expands as it gets hot. They formulate it so that it starts expanding at a certain temperature. They do in fact expand more as they get hotter than the the setpoint temperature, so that if you have a 170 it is beginning to open at 170, opens more at 180, etc. There is a mechanical limit to how much the thermostat element can open and once reached it cannot open more than that. A 170 thermostat will be open more than a 180 at 180 degrees, so it might run a couple degrees cooler in really hot temps, the problem of course is that in really hot ambients and high temperatures both quickly reach the mechanical opening limit and the engine temp is then limited by radiator capacity, so at 95 degrees F driving 70mph on the highway your are running at 194 regardless of which one your have.

 

Thanks, makes sense, but will probably go with 170 anyhow, as I have always gone with the lowest opening thermostat on all my cars (and I have a bunch). Chalk it up to a superstition thing from living in hotter-than-hell Texas.

Jumpering the relay would be the easy move: if there was voltage on the power blade (Pin5 of) the relay.

Looks like some mud dawbers built a rock-hard mud nest, which in turn burned up the condenser fan motor and worse also the wiring from the 100A fuse to Pin5. Crazy to spec a 100A fuse as the 16g wiring would fail before that.

See my new thread on my diagnosis of the condenser fan.

Still going with an inline thermostat, don't want to deal with sealant (at some point you always need to scrape it off), so should I upgrade to the silicone gasket?

 

@austinlandroverbill I used the silicone no problems, but check for leaks after you get it up to temp. I had tighten the housing a bit more, had a tiny leak at pressure.

 

Lots of users have had really good success with the silicone gasket and no sealant from the tube.

 

Thanks. See my condenser fan post if you want to see what happens to the innards of a DC motor when it gets stuck and burns up.

 

as far as myself using the 170..I do not have any codes from that.

 

Thanks, COSitsWORTHit.

First things first, gotta get condenser back online, need to replace both motor and fuse box -- once motor failed (shorted at armature-brush -- see pics in my other thread), it appears to have drawn so much current that it fried the wiring delivering power to the relay for the motor (why a 100A fuse on wiring that probably can only handle 30A remains one of those "Only the English" mysteries).