Triany Switch

[lotusrepair]

Has anyone ever changed a triany switch on the filter? Mainly I want to know if the a/c system has to be recovered before changing the switch or if the switch is connected to a valve. If it is on a vale can it be changed without loosing charge?

Chris

[Brit-Car-Nut]

The trinary attachment connection is a schrader valve and it also has a sealing o-ring at the top of the bore but it will leak a little as you get past the seal but still depressing the valve. It is negligible. Much like when you add air to your tires or just check the pressure. Get everything out of the way and do it as quickly as you can.

Why are you changing the trinary switch? I don't remember ever having one fail or stories from anyone else that has... If you can only get the compressor to run by jumping the connection is it possible your pressure is too low or too high (under or over charged)? I know all things electrical will eventually fail, but it has not been a common fault over the years.

There is also a thermal/temperature switch (I believe it is at the evaporator) that could be flaky or outright bad...

Previous discussion: viewtopic.php?f=134&t=24674#p310809

BTW, that is called the receiver/drier, not the "filter".

[Simon_P]

I don't remember it being a schrader valve, I think it is a straight hole that the trienary switch screws in to. Ie under pressure.

There are some pictures of the replacement filters on here somewhere. The one I had I removed a blanking plug and screwed in the switch.

[Brit-Car-Nut]

Every one I have looked at has a schrader valve fitting. I'll pull a receiver/drier from stock and double check.

[Brit-Car-Nut]

OK, to set the answer straight:

The R12 Receiver Drier (A100P0037F) version HAS a schrader valve and the Trinary Switch (B100P0038F)HAS an internal pin to depress it.

R12 parts

The R134 Receiver Drier (A100P6049F) now replaced by (A100P6061F) DOES NOT have a schrader valve but it comes supplied with a Trinary Switch installed.

The R134 Trinary Switch (A100P6050F) is available as a stand alone part and it DOES NOT have an internal pin included.

Sorry, I didn't want to open the new boxes to take pictures of the R134 parts

[lotusrepair]

The reason I am replacing the switch is that the fans are not coming on. The compressor comes on and the a/c works. Pressure is fine. Jump the switch leads for the fans and they work. The trinary switch has two sets of contacts. The second set for the fans is the problem. The fans work fine for cooling but the a/c uses the trinary sw for the fans.

Chris

[Brit-Car-Nut]

That is wrong.

The two switches in the trinary switch only allow/disallow the compressor to run based on low, normal or high pressure If the pressure is low, the low switch breaks the circuit. If the pressure is HIGH, the high switch breaks the circuit. If it is normal, the compressor gets power to run.

There is no control for the cooling fans in the AC circuit.

Here is a link to the wiring diagram: http://www.lotusm100.com/LEC/M100-AC-Diagram.jpg

Here is the full heater and AC wiring diagram for the SE /R12 model:

Click for full screen

There is no provision for the AC to directly turn on the cooling fans at the radiator.

Here is the cooling fan wiring diagram:

Click for full screen

According to the diagram, there is no A/C circuit to trigger the cooling fans.
I thought maybe the ECM was given that task but I don't see that in the diagram as it would most likely trigger the cooling fan relay and it isn't noted.

In the first diagram, I notice a second feed to the ECM with a Pink/Blue feed. Maybe that is supposed to trigger the cooling fans someway? That is assuming the first feed is to increase the idle.

[Simon_P]

Sorry to disagree John. The Trinary switch provides system pressure High, Low and cooling fans on/off.

In a closed system gas pressure and temperature are related so pressure is used for the temperature switch - I think it is shown in the bottom left of the second diagram.

[Brit-Car-Nut]

I stand corrected as to the high pressure component of the trinary switch.

My excuse: In the mid 1970s, Both Jag and MG had Air Conditioning available and used a trinary switch as a way to protect an AC compressor if the pressure was too low or too high.
It was used simply as a safety protection. I was trained how to diagnose and fix those but they used the switch differently than Lotus does.

The M100 trinary switch still protects for pressure BELOW 30 psi or ABOVE 400psi by turning off the compressor but it also switches the cooling fan circuit after it reaches 200psi.

If the AC/Freon gauges are showing 200psi or more, the trinary switch should be turning the cooling fans on. They will NOT come on if the Freon pressure is below 200psi.

The connection between the ground and the cooling fan relay is via the "Left Hand Front Harness Connection" and the wires of importance are the Black and the "Black with an Orange stripe". Verify that the Black wire has a good ground and then jump between the two connections with the ignition on to see if the fans turn on. If the fans turn on, the switch is bad, If not, follow the Black with Orange trace wire to the Cooling Fan Relay through the "Left Hand Front Harness Connection" to make sure the connection isn't broken or heavily corroded.

The Trinary switch can be removed while the system is charged although you need to be quick to get it off without the schrader valve leaking too much Freon. Disconnect the harness and then thread it off as quickly as possible.

The R12 version uses a different Receiver/Drier than the R134 version so the Trinary Switch part numbers are different

The R12 version Trinary Switch is A100P0038F and they are currently on the "Sell Down", liquidation list at around 5 quid, so if you have R12 AC and are in the UK, you should grab one before they are obsolete. In the US, I have a few R12 switches that I got from Lotus UK and they are $25.00 each.

The R134 Trinary Switch are A100P6050H and are £117.05, so no bargain there.