LR-hobbs · Thursday at 13:30

Hello everyone
Since I took ownership of my 1999 P38 my electric cooling fans have not once gone off even with air con or in stop start traffic.

I've hooked up a separate supply off the battery to test if the fans work which both of them came on.

the only visual issues I can find are both engine bay relays have discolouration on the tops of the relay, other than that the wiring looks ok.

Thanks for reading.

pwood999 · Thursday at 14:39

If you look in RAVE it's all explained. HEVAC enables the fans, but unless pressure-switch-2 engages (247psi) they will be off. The exception on petrol is when the engine gets really hot, the fans will also be turned on.

The dual-pressure-switch only changes the fans from series to parallel to change the speed. This only happens if the AC gas reaches 305psi.

Generally the AC only reaches 200psi unless you're in a particularly hot country !!

pwood999 · Thursday at 14:57

also test the relays

Datatek · Thursday at 17:11

Discoloured relays? Fuse box problems leading to discolouration are not uncommon. Ground the blue/black wire at the tri state switch and see if they run.

LR-hobbs · Thursday at 18:46

pwood999 said:
If you look in RAVE it's all explained. HEVAC enables the fans, but unless pressure-switch-2 engages (247psi) they will be off. The exception on petrol is when the engine gets really hot, the fans will also be turned on.

The dual-pressure-switch only changes the fans from series to parallel to change the speed. This only happens if the AC gas reaches 305psi.

Generally the AC only reaches 200psi unless you're in a particularly hot country !!

View attachment 349162

Ah so generally they won't run, I had fitted a new radiator, hoses and thermostat a few months ago , so the temp gauge doesn't move , it won't have even got up to temperature.

I will get new relays to rule out any mistakes on my end.

Possibly look into a new fuse box if they are even available.

Datatek · Thursday at 19:32

LR-hobbs said:
Ah so generally they won't run, I had fitted a new radiator, hoses and thermostat a few months ago , so the temp gauge doesn't move , it won't have even got up to temperature.

I will get new relays to rule out any mistakes on my end.

Possibly look into a new fuse box if they are even available.

Temperature gauge doesn't move? Something wrong there, sounds like the thermostat is stuck open, lots of faulty ones about, did you test it in boiling water before fitting and fit with the bleed hole at the top?
Fuse box problems can be fixed, often it's just the connectors are slack.

LR-hobbs · 2025-09-05T12:33:54+0100

Datatek said:
Temperature gauge doesn't move? Something wrong there, sounds like the thermostat is stuck open, lots of faulty ones about, did you test it in boiling water before fitting and fit with the bleed hole at the top?
Fuse box problems can be fixed, often it's just the connectors are slack.

Maybe I worded that wrong, the temp needle gets up to the center of the gauge and stays there . Doesn't move at all

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