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#539751 - Thu May 21 2009 01:59 PM Re: Trinary Switch schematic [Re: Flxible]  
beltfed  Offline
Shop Shark
Joined: May 2005
Posts: 1,444
Knoxville, TN
I believe the n/o switch closes at a fairly low pressure increase as history tells me there's not much of a time delay between compressor kick-in and fan turn on. On the subject of a/c cooling. Picture show in August in the south where I live. Temps. in the upper 90's with humidity to match, car left in the sun all day. My southern belle bride jumps in the car with several drops of 'dew' on her upper lip. Note: Southern Belles don't sweat, they 'dew'. She rolls up the windows, starts the engine, and turns the a/c on. Knowing that it going to take several minutes for the engine to heat up and the fan to kick on, and during this several minutes the a/c is running very hard trying to get rid of the heat load in the passenger compartment. With no air moving over the condensor coil mounted in front of the radiator, high head pressures will occur and the system will blow or shut down. This in turn will cause my bride to blow up and you just know where she is going to vent all that heat. Some call it self preservation.

#539755 - Thu May 21 2009 02:28 PM Re: Trinary Switch schematic [Re: Flxible]  
Joe H  Offline
Shop Shark
Joined: Feb 2000
Posts: 4,091
Lee's Summit Mo. 64086
The trinary switch has two internal switches as you know. One controls the compressor clutch, and one controls cooling fan for the condenser.

The A/C system has to have at least 30psi in the system for anything to work (compressor protection). Thats the first switch. Under 30psi the switch is open, no clutch engagement. 30 to 380psi the switch is Normally Closed (active), above 381psi, the switch opens again to protect the compressor. So if the system is full, this half of the Trinary will be NC with the key off, engine off.

At the same time the above is going on, the second switch is Normally open till the system reaches 220 psi (normal operating pressure). Once the system reaches 220 psi the second switch turns on the fan relay though the ground side. This switch stays closed (active) as long as the pressure stays above 220.

The idea behind the Normally Closed at 220psi is to keep from spiking the alternator when the A/C turns on. It spreads the load out a bit. The clutch pulls a lot of power along with the cabin cooling fan, you don't need the condensor fan kicking in at the same time, so there is a few seconds delay while the system builds pressure before the fan kicks on.

If you wire the load side of the relay from a battery post, the fan will run anytime the system is at 220 or above. This will keep the A/C system from going into high pressure on hot days once you turn off the engine to park, the fan will continue to run till it has time to cool the system down.

You can add a third manual override switch to the fan relay. Just use the same ground side as the trinary does and run it parallel to the Trinary.

Recheck your switch with the system running, if the fan doesn't run, follow the wires back to the relay, then the trinary. You should find the problem pretty quick. Just remember you could be looking for a ground and not battery voltage, it depends on how someone has wired it.

There could also be a forth switch involved, a adjustable fan control. It would be wire to the fan relay as well. Its used to turn the fan on and off at a desired temperature, but the Trinary will override it when the system calls for it.
The link above shows how it must be wired for it work correctly.

Never run a second switch in line with the Trinary or you could damage the compressor. You can run parallel switches to control the fan, but don't mess around with the clutch side of the Trinary.

Last edited by Joe H; Thu May 21 2009 06:29 PM.

#539895 - Fri May 22 2009 01:51 AM Re: Trinary Switch schematic [Re: Joe H]  
beltfed  Offline
Shop Shark
Joined: May 2005
Posts: 1,444
Knoxville, TN
Thanks Joe H and red 58. I guess I just didn't what to come to grips with the fact I'm going to have to open the system up and replace the trinary switch. Well, as the old saying goes..."On rainy days I work on old tin, on pretty days I drive old tin." Let me see now....When is the weatherman saying it's going to rain?

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