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Old 11-10-2011, 01:23 PM   #1 (permalink)
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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.

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Last edited by SentraSE-R; 11-10-2011 at 04:00 PM..
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Old 11-11-2011, 12:17 PM   #2 (permalink)
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I emailed elabtronics yesterday. No reply.
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Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
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Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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Old 11-11-2011, 12:49 PM   #3 (permalink)
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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.
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Old 11-11-2011, 04:09 PM   #4 (permalink)
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looking at how that works I would use it as an automated alternator kill switch
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Old 11-12-2011, 01:26 AM   #5 (permalink)
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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.

Last edited by 8307c4; 11-12-2011 at 01:35 AM..
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Old 11-12-2011, 02:13 AM   #6 (permalink)
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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?
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Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg

Last edited by SentraSE-R; 11-12-2011 at 02:26 AM..
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Old 11-12-2011, 03:45 AM   #7 (permalink)
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Is this kit the type of thing you are looking for?
"Car Air Conditioning Controller Kit"
Car Air Conditioner Controller Kit - Jaycar Electronics
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Old 11-12-2011, 07:44 AM   #8 (permalink)
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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.
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Old 11-12-2011, 08:55 AM   #9 (permalink)
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Quote:
Originally Posted by D.O.G. View Post
Is this kit the type of thing you are looking for?
"Car Air Conditioning Controller Kit"
Car Air Conditioner Controller Kit - Jaycar Electronics
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.
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Darrell

Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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Old 11-12-2011, 08:57 AM   #10 (permalink)
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Quote:
Originally Posted by SentraSE-R View Post
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 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...

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