Got started on this modification. Making the AC high pressure switch kick the fans onto high speed instead of low speed was easy. I took apart the fuse block, popped the relay sockets out, and moved the ground wire from the high pressure switch over:



One tip: When you want to remove one of the terminals from a relay base without having them all fall out pop the relay back in before you remove the locking cover. The relay pins will hold everything in place.

Tomorrow I'm going to get the low speed hooked up to the compressor turn on pin of the Klima relay and the radiator temp switch I installed.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Finished this up tonight. I'm very pleased with the results:

Elec fans run on low speed any time the compressor clutch is pulled in.
Elec fans run on low speed when the lower rad hose temp is 75*c and shut off at 65*C. (This keeps the temp gauge below 90*C)
Elec fans run on high speed when the water outlet temp is 95*C --> added a 1k resistor in parallel with the ACC temp sensor.
Elec fans run on high speed when the refrigerant pressure is over 250 PSI.

The belt driven fan and shroud are deleted.

Getting the compressor output to turn on the low speed fans was easy, I just added another relay to turn the + signal into a ground signal. There were no free relay locations left on my car, so I just tucked it into the bottom of the fuse box. For the extra relay ground I tapped into the ground wire for the power window relay connector (which is why it's loose in the above picture).

I exchanged the 30A low speed fan ice cube relay for the original 40A high speed fan relay, and got a new 40A relay with a replaceable fuse.

What's left to do: I need to top up my AC charge as it leaked out a bit over the winter. I also need to seal up air leaks around the factory pusher fan shroud, and between the AC condenser and radiator to maximize the cooling power of the fans.

As temps get warmer here in VA I'll post an update.

Thanks,

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.