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Author Topic: Dash ac trinary switch  (Read 411 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 .

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 525, Vicksburg, CAT C13, Allison 4000MH, HydraLift
Orlando, FL

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.

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 525, Vicksburg, CAT C13, Allison 4000MH, HydraLift
Orlando, FL

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

Timothy Weir

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Re: Dash ac trinary switch
« Reply #5 on: August 19, 2019, 04:12:55 PM »
OK, Got it figured out.
I pulled the switch and hooked it to nitrogen and my gauge set ran pressure tests to determine exactly how the switch works. The switch is labeled dc, overide, thermo, comp. There are two switches in there dc and overide and thermo and comp. DC/overide makes at 200psi and when pressure drops it breaks at 150. I ran it to 375 and never broke. Thermo/comp made at 30 psi and broke somewhere around 300 ( I forget that number right now). Once I knew this I knew how things needed to be hooked up. As we all know, when these old coaches get worked on through out the years you never know what monkey worked on it before. Mine only has three wires leaving one of the spades not used. I had 12v, fan and comp. What I determined was that I needed 12v to each switch so I made a jumper from 12v to thermo. I then put the fan on overide and compressor to comp. When I turn on the switch it makes the switch for the compressor and as the pressure rises on the high side it brings on my condenser fan motor to regulate the head pressure, (It's a fan cycling switch like we use to control head pressure). So now if the head pressure reaches 300 it drops the compressor and keeps the fan running to lower the head and when its low enough it will remake the compressor. Like wise if I run the air in colder weather and its not warm enough outside to keep the head pressure up the fan will cut at 150 until the head comes back up to 200 and keep cycling.
   I know I am saying a lot here and some of you say "of course" but finding what a "trinary switch" actually does crucial for me to understand how to hook it up. Maybe someone else could use it. We don't use trinary switches in the ac world but use the same switches singularly for the same results.
   Since my trinary had a bad schrader behind it I had to pull the r12  to do this so I used this opportunity to convert it to 134a. She is working like a charm.
   Thanks for all the input. 

Mike Shumack

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Re: Dash ac trinary switch
« Reply #6 on: August 19, 2019, 05:09:39 PM »
Thanks for the follow up.
Being a "visual guy" I wrote your findings on my "Trinary Switch drawing". If I understood you, this is what you have:

What were your High and Low pressures (at what ambient air)? Do they come close to chart in the previous post?




- Mike

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

Timothy Weir

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Re: Dash ac trinary switch
« Reply #7 on: August 19, 2019, 07:34:23 PM »
Your drawing is correct. I have some photos but not sure how to attach them. When you look at the diagram on the switch itself starting left to right on the pins would be 12v- bypass-thermo-comp. I would have labeled them clockwise 1234. Your drawing is correct though. As far as my pressures I’m probably undercharged but sitting still and just the fan at the condenser my head pressure was running a little higher and my suction was trying to hang about 26. I shut it down and cleaned up some and started again and it settled in at260/26 at87 outside air and I had about 58 degree air and snide. I will revisit it this week when I uncover her to move her to make parking room in my driveway for a family gig.