Primative AC fan control

[Emit]

Just got my AC working for the first time every - its very cool (!) and I'm delighted, but I have to say the control logic is a bit primative:

The general problem is that the radiator fans are lockstep with the compressor, bitsynchmaster's fan relay would sort that out, but there is another annoying issue that the fans run if you have the AC on but the car hasn't started yet - it is something I can live with, but its a big electrical draw just before ignition and in the very early warm up stages where the fan isn't required yet (at least I assume that the rad fans are not needed in the first ten/twenty seconds while it builds pressure).

So would it make sense to put in a starting delay too, so that the fans don't run for the first X seconds of initial power? Or am I overthinking this?

[Bitsyncmaster]

Your compressor kicks on also if you leave the AC on when starting the car. I always try to turn off the AC before I shut down the engine. You would need to delay the compressor signal.

[Emit]

Your compressor kicks on also if you leave the AC on when starting the car. I always try to turn off the AC before I shut down the engine. You would need to delay the compressor signal.

Ooo that's a very good point, that's quite the load on the engine for a cold start - I've seen folks put noise/voltage feedback suppression and/or a relay so that the clutch load isn't running through all the switches, [thinking out loud] that would be an opportunity to introduce a delay to the compressor when doing that work.

I feel a summer project coming on.

[David T]

Ooo that's a very good point, that's quite the load on the engine for a cold start - I've seen folks put noise/voltage feedback suppression and/or a relay so that the clutch load isn't running through all the switches, [thinking out loud] that would be an opportunity to introduce a delay to the compressor when doing that work.

I feel a summer project coming on.

If you have a good battery this should not be a problem as long as you get the motor running quickly once you turn the key. There are all kinds of things you can do to "modernize" things to make the car act more like a computer controlled car. To some owners these things just make the car more unique and period correct. To others it is just adding another thing that can malfunction. Just because you CAN do something doesn't always mean you should.

[dn010]

While I do have my car set to not engage the compressor when starting (EFI), another thing to think about is the chance for mold from the water sitting in the box. In any of my cars, I shut off the A/C a few minutes prior to arriving to my destination, if I am going to be stopped a while, and just use the fan so the water clears out. In some of them you can definitely smell the difference in the air if it was parked overnight after leaving the A/C on.

[Emit]

another thing to think about is the chance for mold from the water sitting in the box.

Good point, I've just rebuilt the HVAC box so a minimum of mouse bedding and leaves, but you're correct


...Just because you CAN do something doesn't always mean you should.

Oh yeah that's nearly a religious topic, ship of Theseus, what "good" means etc., luckily I've made peace with where my line is on that; and it includes reversible hidden electrical modification to improve the reliability, safety or drivability of the car... and the be honest no sane person "should" have a DeLorean, we're all firmly in the "can" camp.


For reference the flyback diode to stop the battery light from flickering and protect anything electronically sensitive is discussed here: https://dmctalk.org/showthread.php?12203-Electrical-noise-fix-for-AC-compressor-clutch

[Timeless]

While I do have my car set to not engage the compressor when starting (EFI), another thing to think about is the chance for mold from the water sitting in the box. In any of my cars, I shut off the A/C a few minutes prior to arriving to my destination.
I do the same. I also installed stainless mesh under the cowl panel to cover the air inlet to stop debris from falling into the blower box.

[Josh]

If you are concerned, just install a relay between the compressor and the switch. Have the coil tie into the rpm relay so the ac compressor only kicks in when the engine is running.

[Bitsyncmaster]

If you are concerned, just install a relay between the compressor and the switch. Have the coil tie into the rpm relay so the ac compressor only kicks in when the engine is running.

RPM relay turns on with first ignition pulse. You really need a time delayed relay.

[Emit]

I've got a few time delay relays on the way to me already, I'll let you know how it goes. Most of the relays are to delay the OFF time, not the on time, I suspect for things like courtesy lights, keep fans running after key-off etc.

Yes, I have to drive the delay from the ignition to control the call for AC - I can't just delay the AC signal as it would be delayed on every call for AC.

I appreciate that this is overengineering for an issue that isn't actually a real world problem, it's more of a fun project.