Timer for airconditioning?

[thuur]

Hi,

First of all: sorry if this isn't allowed, I couldn't find anything in the rules that it might be unwanted. If so, just delete this thread or move it to a better place

I've been looking for a DIY schema to make a timer. Well lots of those around, but let me explain my need.
I have a nice car with a pretty good AC system (and sound system ). The weak spot of this system is the evaporator. It costs about 120 euros but it takes 8 hours in the workshop to replace (complete dash has to be removed!). These evaporators literally rot from the outside in due to moist. Expected life span: 2 to 4 years

The only life prolonging thing you can do is to blow the fan on maximum speed for about 5 minutes after you turn off the engine or AC.

So, I'm looking for a timer that actives my fan for about 5 minutes after I turn off the engine (or a 12V supply gets disconnected). I don't mind having an extra switch to choose between the timer or not. I'll just set it on 'auto' (the same as the climate control) by default and incidentally on OFF when I didn't use the AC.

I have all the schematics of my car so turning the fan on and off will not be a problem.

Complete circuits and designs would be awesome, but I'll be grateful with some links or detailed ideas as well!


Thanks for looking!


Regards,
A

[star882]

Charge a capacitor from the A/C compressor power with a diode and use a transistor to turn on a relay that keeps the fan on.

Check your local HVAC supply store. They probably will have a nice little module that does exactly what you want (it's something like an "off delay timer"). Probably wouldn't cost much more than a DIY circuit anyways.

BTW, pretty much all home A/C systems keep the fan on for a minute or two after the compressor turns off.

[Ron E]

You live near the sea?

There are two things you can do other than what you are trying:
Have your evaporator dipped in a coating (Heresite) or
Use a copper finned copper tube evaporator

[thuur]

Thanks for the replies guys!

I do not live near the sea. The evaporators are just bad quality. There is a choice between 2 or 3 brands, but no other materials than some tin can metal.

I will have a look at my local shop.


R,
A

[star882]

Maybe zinc plate the evaporator to protect it from corrosion?

[SoundOff]

A turbo timer would do the trick. These are intended to keep the engine running at idle for a few minutes after shutdown to cool turbo bearings down, then switch off. You should be able to adapt one for the vent fan.

Colin