Yes but do the AC Condenser fans also run if the engine water temp is too high? I don't think they could run in high speed AC off so I think the electric fans are AC only.

A lot of the AC Cooling fan operation descriptions and diagrams don't seem to be correct or very clear in Rave. Only that fuse box relay wiring schematic gives you the true operation (thank you). Pretty sure the electric fans can only run high for AC because you need the pressure switch over 21Bar. Do you think that's correct?

So a manual two 'speed' switch means they could be used in low and high rather than an aftermarket fan unit.

If they're just AC fans (No engine cooling requests) a dual position switch could earth pin2 RLY 18 (for low speed) and then pin2 on RLY13/14 to run high speed.

Turns out it's the HVAC Controller C244 pin8 (output) not sending 0V to GEMs C507 pin30 (input) when AC on engine running. The GEMs should then send C505 pin3 (output) to pin2 of Relay18 running the fans in low speed. I get no earth on Relay 18 pin2 AC on engine running but if I ground externally the fans run low speed. The GEMs ECU is working and will drive the low speed fans via a NanoCom request. Also whatever the NanoCom check is for AC Request is, it's misleading - it doesn't seem to relate to the output of the HVAC Controller as I get a 'Yes' for AC request but no ground out to GEMs.

I'd like a working HVAC Controller but the easy fix is to put a Relay18 pin2 ground switch in. The fans will still run in high speed like this for AC.

I'm intrigued now about how engine cooling fan requests work. Low speed would be the same as AC low speed but does anyone know how High Speed engine cooling works since AC Dual Pressure switch won't be in play?

Thanks, I'll check Relay18 but confused. On Nanocom you can run low speed fans from GEMs (both run low speed so relay 18 must work?) and you can also check the AC Request from HVAC which also works - I have both except no low speed fans AC on. Guess I check the relays anyway.

Thank you. Yes they stay at 4.6 to 5V - two new sensors needed then. I expected an O2 sensor error but it's early system I suppose. Guessing the max short term trim is 38 then? Anyway thanks very much for your help.

Hi, thanks for your reply - that description helps a lot with relay operation - I really struggled with that and couldn't figure out the basic operation - thank you! So now I know the LHS motor should run low speed as soon as there's an AC Request HVAC to GEMs, and the RHS motor should run low speed too if the X315 switch goes over 21 Bar, I know I've got to check the HVAC panel plug C244 pin 8 blue/black wire (condenser fan motor control). This is the HVAC request to the GEMs ECU for fan motor control. If I drive the fans from the Output Options on Nanocom both fans run at low speed - not sure why both run (faulty close X315 pressure switch?) but anyway at least I know they both work! Now I can measure HVAC C244 pin8 to see if it's high or low and if it's high (no request) with AC On I know the HVAC panel is faulty. I can even feed a 0v to pin8 wire and see if the LHS fan runs. Thank you! Hopefully this sounds sensible!

I've read RAVE, I've looked at the confusing high speed/low speed fuse box relay circuit and still have no idea why my low speed fans don't run. If I jump 13/14/18 relays both fans run, if I use Nanocom (GEMs ECU Output Function) to run low speed AC fans they both run. On a 40degC days here stuck in traffic my high speed fans run but never the low speed. My AC works well but even with a new fan viscous coupling the performance drops at idle. As far as I can tell there needs to be an HVAC low speed fan request, a GEMs fan request (for 12V and Ground) and the the two way/low speed AC pressure sensor needs to be closed. Suspecting the HVAC controller output but does anyone know when the HVAC is supposed to request low speed fans so I can check the output? Thanks - going crazy on this one.

Hi All, new member here so hope this post is okay. I've got a 1997 GEMs 4.6L that runs very rich. Using a Nanocom I can see my short-term trim is 38 and my long term trim is zero. Both O2 sensors appear to be working and with light driving they run at around 4.6V to 5V and both banks run in a similar way. The MAF seems fine - sensible voltage and mass flow numbers and so does the TPS. I've tried resetting the adaptive, but the P38 always returns to this high short-term trim number. I always run a minimum of 95Ron but 98Ron makes no difference. Any idea what I should try to fix this? So far I've cleaned the MAF (with MAF cleaner), changed all the plugs for NGK plus OEM leads - the original plugs were the richest I've ever seen on a fuel injected car! My next step would be to change the O2 sensors except they seem to both be working. Any help really appreciated!