Trinary Switch

[Luckyone]

I want to try & find out if there’s any pressure left in the A/C system, but the radiator & pipe work plus a load of other stuff is out of the car right now, so can’t do the easy check of the compressor clutch. So I was thinking I should be able to take a reading from the trinary switch with a multi meter, any one know I’d go about doing that?

The A/C has been in it’s usual non operative state for quite some time now so I guess there isn’t any gas left, but I don’t want to go disconnecting the A/C pipes if the system is still full of nasty gas. Also I can’t do more than 200 miles with out having to clean an oily film of the inside of the windscreen, which make me wonder if it’s the cooler box inside the wing that has a slight leak of refrigerant, that’s the only way I can think oil could get to the inside of the windscreen.

[SimonJ1966]

I'm not sure that a reading from the trinary switch will tell you if the system is completely empty - iirc it will go open circuit if the pressure is both too high or too low. Just because the pressure is too low it doesn't guarantee that the system is empty...mind you if it hasnt worked for some time it is likely there is nothing in there.
Oil on the inside of the windscreen sounds like you could have a leak in the evaporator - the heat exchanger inside the cabin where the warm air has it's heat extracted by the refigerant?

[Tanguero]

You need to put a gauge on the low side port (by the compressor) without the compressor running if you want an actual pressure reading.

If you suspect that the system is completely empty and just want to check you can (AT YOUR OWN RISK!!) nudge the schrader valve core in the low side port with a narrow screwdriver and see if it hisses. Do not put your face near it to listen, wear gloves and preferably stand so the port is pointing away from you. You seriously do not want a face full of refrigerant.

[Luckyone]

Thanks very much for the replys, quite right no messing with any measurements needed. One tiny puff of gas then nothing. So now I just have to try & remember what I uesd to connect the compressed air line up with when I was chasing leaks in my other car.

The only problem is the A/C was one of my main reasons for not lifting the body totally off the chassis, off to find a block & tackle now.....

[Demondad]

SimonJ1966 said:

Oil on the inside of the windscreen sounds like you could have a leak in the evaporator - the heat exchanger inside the cabin where the warm air has it's heat extracted by the refigerant?

Ahh I have been wondering what this oily film is. Is this leak relatively easy to repair? It's a right nuisance to clean the windscreen every journey.

[Luckyone]

Demondad said:

SimonJ1966 said:

Oil on the inside of the windscreen sounds like you could have a leak in the evaporator - the heat exchanger inside the cabin where the warm air has it's heat extracted by the refigerant?

Ahh I have been wondering what this oily film is. Is this leak relatively easy to repair? It's a right nuisance to clean the windscreen every journey.

In a word NO! The oil on the screen is a right pain though isn't it, glad to hear I'm not the only one.
Now I've established there is no gas left in the A/C I'm going to pressurise the system with free(ish) compressed air & then listen for a leaking hiss from the OS inner wing.
If it is the heat exchanger in the cool air box, then assuming it can be fixed once out, the pedal box & steering column have to come out. Then the A/C pipe work is disconnected & the cold air box is removed from the footwell, threading the pipework back through the inner wing behind it. The manual says to use the inspection hatch in the wheel arch but I haven't got one, may have to break out the jigsaw, but don't want to cut the pipes
Don't forget you'll need to be sure all your bleed nipples are ok before draining the brake fluid
I can let you know how I get on if you like.

[Tanguero]

Don't forget that you must change the receiver/dryer (inside the front nearside wing) if you open the system or put damp compressed air into it.

[Luckyone]

Tanguero said:

Don't forget that you must change the receiver/dryer (inside the front nearside wing) if you open the system or put damp compressed air into it.

Ah thanks, I had forgotten that. APM Andy had told me that a long time ago, he also said it is meant to be changed every so often anyway, but it hardly ever is.
My air should be dry as my line comes right from the filter / trap, but I will be opening the system.

[Demondad]

Think I'll carry on cleaning my windscreen daily!!! Aircon works fine, so if it aint broke......

[SimonJ1966]

Don't put compressed air into it - if you can get it, pressure test with oxygen free nitrogen (dry nitrogen). The less moisture in the system, the better.

[JensenA]

I doubt very much that you will be able to 'hear' any leak. Bite the bullet and take it to an Air Con specialist and explain what's happening. they may even do it for free. They will Re-gas it and put a Dye in. The Dye is visible under UV light, that's the only way to check for a leak. There is an access hatch in the rear of the wheel arch for the hot air fan, It's well hidden by sealant, just scrape away the crap and you'll find the self tapper heads.

[Luckyone]

JensenA said:

I doubt very much that you will be able to 'hear' any leak. Bite the bullet and take it to an Air Con specialist and explain what's happening. they may even do it for free. They will Re-gas it and put a Dye in. The Dye is visible under UV light, that's the only way to check for a leak. There is an access hatch in the rear of the wheel arch for the hot air fan, It's well hidden by sealant, just scrape away the crap and you'll find the self tapper heads.

That would be the easiest way, but the body is half way off the chassis now so taking it anywhere is not an option. I took my other motor to the local place to have that dye put in & they charged me £90 to tell me it was leaking somewhere down the bottom, but they couldn't see where with out spending me lots more for them to take more bits off it to see. I got it home, used compressed air to find it was the condenser & fixed it with a £50 second hand one.
APM Andy had to cut a small hole when he replaced the Cerbs A/C pipes years ago, he said there should have been a hatch but there wasn't one, didn't seem to think it was odd there wasn't one, it is a TVR after all...