1978 XJ6L A/C cycling?

I don’t where the fan relay is on a Series II, sorry.

On a Series III it’s the red, round relay on the radiator mounting panel, just to the left of the radiator. Might be the same?

Cheers
DD

yah it is the same, that’s the one i changed i am just double checking, i truly wanna see this thing turn on so i know the circuit works, is the temp sensor on the radiator just a resistance or an actually switch i am trying to find out a way to just turn it on and see if it works and i may just hard wire it to a button/switch

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The temp gauge should read a tad under halfway, ColdDna - straight up is around 90C…

With the temp reading steady; you are not overheating. The gauge reading is caused by a wrong two-wire sensor with wrong resistance - the gauge is served by a single wire, as Doug fully explains.

That said; with suspect cooling problems - get an infrared thermometer. It will accurately measure temperatures, removing all doubts - and direct efforts to areas that may need them…

The temp sensor on the radiator is a switch - activating the fan relay. Nominally; shorting the two wires together should start the fans? The fans are usually supposed to come on at 95C - and the sensor should be tested.

If it works as it should and the fans doesn’t come on except in extreme situations - your cooling system is working as it should. No need for a manual switch control of the fans in that case…

Frank
xj6 85 Sov Europe (UK/NZ)
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There are a couple of different sensors with different calibrations.
When I replaced mine the new one was showing 5° warmer than the old one.
You should measure it’s resistance and compare it with it’s resistance / temp chart.
Even better, check the actual engine temperature with an IR thermometer.

These are the charts I have, I think they are more or less correct:

DAC3105
0° 1.1 kOhm
10° 871 Ohm
20° 680 Ohm
30° 530 Ohm
40° 412 Ohm
50° 319 Ohm
60° 245 Ohm
70° 187 Ohm
80° 141 Ohm
88° 112 Ohm
90° 105 Ohm
92° 99 Ohm
100° 76 Ohm

DAC2583
20° 980 Ohm
30° 600 Ohm
40° 400 Ohm
50° 290 Ohm
60° 210 Ohm
70° 150 Ohm
80° 105 Ohm
88° 80 Ohm
90° 75 Ohm
100° 56 Ohm

Servicing your radiator is a must regardless…

Best,
Aristides

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