Air conditioner disconnect circuit
 

Has anyone done this load-related AC compressor disconnect mod? It seems simple enough with the adjustable low voltage disconnect switch discussed in the article.

Unfortunately, the eLabtronics LVD switch appears to be unavailable from either Autospeed or eLabtronics. The articles are 3 years old, and clicking on purchase links leads to dead ends.

A search for adjustable LVD switches finds plenty of them, but they're all designed for battery switching in solar panel set-ups. None have the 0.1 to 4.5 volt trigger level needed to sense our TPS circuitry. I'm stuck. Any suggestions? I could probably build a circuit if given detailed directions.

I emailed elabtronics yesterday. No reply.

You should be able to make a circuit using a voltage comparator like an LM211 or LM311 to do what you want.

For reference, you can look up autospeed's closed loop monitor circuit. I believe they use a similar circuit to power that. It would work essentially the same.

looking at how that works I would use it as an automated alternator kill switch

I wouldn't fool around with that system unless you know in intricate detail what each part is called, what it does and what it takes to replace it, how it works and how much it costs, which way the freon flows, what type and viscosity of a/c oil your car's system takes, which is the high and the low side and so on...

Maybe the only thing I can tell is you can manually control the compressor from cycling via the wires leading to the dryer / accumulator / receiver but it's generally only used for testing, you see where this is leading in terms of a failure, there exist several components to an automotive air conditioning system and if any of them fail you're looking at several hundred dollars and that's just for starters.

In most cases, the mere diagnostic of an a/c system costs north of $100,
that's just for them to TRY and find out what is wrong with it.

Don't be the next two thousand dollar a/c repair horror story, if you like your air conditioning to work, then don't fix it.

That having been said, by disconnecting the plug at the dryer / accumulator / receiver, the compressor won't come on at all.

Thanks, Daox. I should be able to use the closed loop monitoring circuit by having it monitor the TPS voltage, using the LED light signal as a triggering circuit to a relay to open the AC compressor circuit.

8307c4, I understand from your post I shouldn't shut the compressor alone. If I simply open the AC on/off switch with the relay, that should avoid your concerns, correct?

Is this kit the type of thing you are looking for?
"Car Air Conditioning Controller Kit"
Car Air Conditioner Controller Kit - Jaycar Electronics

On my 1975 Camaro, I had installed a vacuum switch that simply opened the circuit to the compressor clutch. I didn't have any problems with the AC from that setup. As the clutch normally cycles on and off, I don't see any reason why it should cause a problem. But then the AC setup was much simpler than some of the newer systems.

D.O.G.,

Yes, that's it exactly! Thank you. I've ordered a Jaycar kit for my car, and will also order the parts to attempt a scratch build of my own modified closed loop monitor for my wife's car.

I went looking just now and can see your jam-up. I tried changing some search terms, going for fewer, for more, for synonyms. No luck. This is a really interesting idea, though. I wish I could be more helpful. Good luck...

CACivic, D.O.G. found a current kit for me. This is too cool, getting overnight help from a fellow ecomodder in Australia. Autospeed, eLabtronics, Silicon Chips, and Jaycar are all Australian firms, so the Aussies definitely see the usefulness of this mod.

Wonderful. EM is too cool. Post your build when the time comes?

Sure, if it's successful. I'm also looking at LM311 and comparable voltage comparators (e.g. LMH7220) to built my own circuit. Again, you'll get a DIY if it's successful.

Got my kit. I haven't built an electronics kit with PCB & resistors in 40? years. This is going to be a challenge!
http://i1179.photobucket.com/albums/..._0122Small.jpg
http://i1179.photobucket.com/albums/..._0124Small.jpg

One thing I discovered recently: My xB runs its radiator cooling fan whenever the AC is on, regardless of coolant temperature.

Supplies look intimidating. Good challenge. :thumbup:

anyone have a schematic? id like to build one of these

Buy the kit linked above. The developer put a lot of thought into it. He filters and traps the signals in more ways than I ever considered. The main function is to cut the AC compressor when the TPS voltage exceeds a preset limit.

But the circuitry includes a manual override, and three different modes involving high, medium, and idle TPS, interacting with vehicle speed.

Settings include multiplier value, adaptation setting (modifies the length of the cool-down period), logging period, and retrigger period.

The developer says there are 1500 lines of code in the EPROM. Way too complicated to do myself.