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probably not.
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Posted by sloopjohnb (more from sloopjohnb) on Tue, 31 Jul 2007 05:25:22 Share Post by Email
In Reply to: is it o.k. to temporarily bypass the a/c relay ?, John Daikhj, Tue, 31 Jul 2007 02:38:16
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The relay just handles high current..you could use a 30amp switch instead but the problem is that there are several other controls that work the relay...your finger just ain't gonna get it.

1. low pressure switch...shuts off compressor if refrigerant pressure drops too low. saves compressor. If you don't car about low pressure, ok.
2. high pressure switch...does same thing if pressure gets too high. Too high pressure can burst pipes or condenser although no shrapnel generally. If you don't car, ok.
3. full throttle cutout..chops compressor at full throttle...if you don't care, ok.
4. Depending on your system, the capillary tube/thermostat cycles the ac compressor relay...bypassing the relay causes continuous operation of the compressor and possible evaporator freeze-up from moisture in the air. This happened to me on a regular basis when crossing the Chesapeake Bay bridge from the East to the West on Sundays coming back from the beach. Drove me nuts for four weeks before I finally figured out the increased moisure and continuous operation (and a dislodged capillary tube) from Rehoboth Beach to the bridge was enough time for the evaporator to freeze solid. Took maybe 20 minutes with ac switch off to thaw the coil and then another 2 hours to freeze it up again. Point is that if you bypass the relay, you remove the capillary tube/thermostat control over the evaporator temperature which will probably freeze up (a block of ice for an evaporator makes a poor heat transfer device).

Lastly, I'm not sure the relay doesn't shut off the compressor when the ignition is off or the engine is starting...there might be a main relay that supplies power to everything but you'd have to check if the feed to the ac relay is hot with the switch off. If the feed is hot, it wouldn't be a good idea to bypass the relay because then the ac compressor clutch is hot all the time which would kill your battery, probably overnight.

On the other hand, except for the last item (and you could probably finesse that one if you remember to shut off the AC when you shut off the engine) you could, with some risk, bypass the AC relay. I'd probably do it if I were on the road and couldn't replace the relay.

posted by 140.185.5...
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