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Author Topic: Dash ac trinary switch  (Read 145 times)

Timothy Weir

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Dash ac trinary switch
« on: August 15, 2019, 03:32:21 AM »
I am stumped. I am working on my dash AC and found that the trinary switch has 12v to it but never makes the switch to power the compressor and condenser fan motor. I jumped the switch to power them and charged the system to zero bubble with a low side of 30 psi. My arms are to short to reach the high side port. I have replaced the trinary and it still doesn't make the switch. I do ac for a living so I understand it all but am kerflempt on the pressure switch not making. If I have 12v when i place a call for cool to the trinary but no voltage to other terminals is it likely I just got a bad switch? or am I missing something. It is a red dot trinary on a 93 contessa. Thanks .
Tim
1993 Beaver Contessa Signet 38'
Cummins C8.3-300, 300hp
Gillig Chassis

Mike Shumack

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Re: Dash ac trinary switch
« Reply #1 on: August 15, 2019, 11:04:04 AM »
You could have a bad switch - but without knowing the high side pressure it's hard to diagnose.
The Trinary switch protects system from too low AC pressure (30 psi and under) and too high pressure. And it turns on the Condenser fan (for those coaches with a front mounted Condenser).
Without the switch closing the fan wont run and that means much higher "high side" pressures - and possibly so high the Trinary switch is opening to shut off compressor (protect system). See the attached PDF file.

I assume you are using R134a refrigerant. On a warm day (85 degrees) you would expect to have around 50 psi low side and 230 psi high side. You didn't say what the air temp was, but you cant charge by "bubbles" (that was for the older R12 systems and not too reliable then). You really need to know gauge pressures.



- Mike

'05 Beaver Patriot Thunder, Vicksburg, CAT C13  525HP, Allison 4000MH, HydraLift

Timothy Weir

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Re: Dash ac trinary switch
« Reply #2 on: August 15, 2019, 02:39:34 PM »
Not knowing my high side is why I went to zero bubble. that would just insure that I had a steady flow of refrigerant to the txv. I did for get to mention it is r12. I'll be switching over in the near future since I don't have a large quantity of 12. I actually metered the switch as I added and that portion of the switch never made, high or low. This is one of those things like condemning a circuit board in a residential system, I make myself crazy before hand. There seems to be so little information on those trinary switches and some it conflicts. I wanted to run this up the flag pole before unloading a parts cannon. Guess I will order a new switch and see. Thanks for the input.
Tim
1993 Beaver Contessa Signet 38'
Cummins C8.3-300, 300hp
Gillig Chassis

Mike Shumack

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Re: Dash ac trinary switch
« Reply #3 on: August 15, 2019, 02:57:40 PM »
You said you already replaced the Trinary switch once. It would be odd to have that new switch fail (of course it does happen).
As you know R12 pressures run lower than R134a, so I wonder if the Trinary switch you bought is setup for R134a pressures (meaning the 30 psi low side pressure you have is too low for the Trinary switch to remain closed). Although the PDF on the switch specs says the low side range is 15-30 psi (so does the switch open at 15 and close at 30 psi., or does it open anywhere below 30 psi?)

I'm told our Coaches use the "Red Dot" switch. http://firewall.reddotcorp.com/mobile_ecomm/find_truck_part.asp?oem=VOLVO/WHITE%20GMC&model=RC&catid=71&catname=CONTROLS%20(ELECTRICAL%20&%20REFRIGERANT)
There are two variations - a normally open "fan relay" contact, and a normally closed contact. Otherwise they are all the same (expect the mounting thread).

Good luck.
« Last Edit: August 15, 2019, 03:05:29 PM by Mike Shumack »
- Mike

'05 Beaver Patriot Thunder, Vicksburg, CAT C13  525HP, Allison 4000MH, HydraLift

Steve Huber Co-Admin

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Re: Dash ac trinary switch
« Reply #4 on: August 16, 2019, 12:53:30 AM »
Tim,
Keep in mind that if the fill ports are in the front of the coach, charging to the values shown in the chart will problbly result in overcharging. The chart is applicable to systems where the ports are relatively close to the compressor.
Steve
Steve
2015-          07 Contessa Bayshore C9,  400 hp
2013-2015: 00 Marquis Tourmaline, C12, 425 hp
2005-2013: 01 Contessa Naples, 3126B, 330 hp