Air con help - TX valve

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mat_fenwick
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Air con help - TX valve

Post by mat_fenwick » Mon Feb 06, 2006 3:08 pm

I have finally got round to working on the air con swap, all the bits are out of the donor car ready to be installed. I remember Tom suggesting I should uncrew (counting the turns) the brass plug on the TX valve and pop in a new green O ring. Firstly:
1. Is this the plug that has the D shaped ring on it?
2. I don't think it is leaking at the moment so am I likely to make things worse by taking it to bits? I would like to replace it but I have a worry of things flying out everywhere!

Also, can anybody tell me the function of the 2 wire temp switch on the thermostat housing on air con cars? One wire obviously to the dash lamp, but does the other wire break an earth contact when it gets too hot, to cut out the compressor?

Thanks!

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Re: Air con help - TX valve

Post by AlanS » Mon Feb 06, 2006 8:37 pm

mat_fenwick wrote:I have finally got round to working on the air con swap, all the bits are out of the donor car ready to be installed. I remember Tom suggesting I should uncrew (counting the turns) the brass plug on the TX valve and pop in a new green O ring. Firstly:
1. Is this the plug that has the D shaped ring on it?
2. I don't think it is leaking at the moment so am I likely to make things worse by taking it to bits? I would like to replace it but I have a worry of things flying out everywhere!

Also, can anybody tell me the function of the 2 wire temp switch on the thermostat housing on air con cars? One wire obviously to the dash lamp, but does the other wire break an earth contact when it gets too hot, to cut out the compressor?

Thanks!
The question about the wires and the sensor, should be answered here:

http://www.aussiefrogs.com/forum/showthread.php?t=9161

Regarding the T/X valve, this is what it looks like on a BX:

http://www.aussiefrogs.com/forum/attach ... entid=2998

These are the types used on all of ours. They're known as an "Eaton block valve" whereas the one Tom spoke of was obviously one of the earlier externally balanced variety. As you can see, the only things on this are actual fittind that screw in and screw up tight to seal. The older types had an adjustment on the valve and this is possibly where you're getting confused.
If the system you have is an R-12 system, then the "O" rings need to be changed wherever possible. The R12 "O" rings were black rubber looking things whereas the later gasses take a green neoprene type. Left in, the black ones simply perish and cause leaks.
You will also need to check gas type for the sake of the oil. R134a takes what is known as PAG oil (around 150mls) and is incompatable with original R12 oils.
Read this in detail as whilst it may seem a long drawn out thing now, it should all make sense as soon as you start doing the job. I deliberately over detailed the report of this project so that anyone doing what you are, can see possibly every trick and trap as we came across them and whilst it does look daunting, you should find most things have been covered thoroughly in the process; it's not as bad as it may first read.

http://www.frenchcarforum.co.uk/forum/v ... hp?t=11605


Alan S
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Post by Way2go » Tue Feb 07, 2006 2:16 am

Amazing in depth knowledge here Alan, which prompts a few questions from me if I am to ressurrect my system which has needed recharging.

1) Would a 1991 GTi with Aircon be R12 or R134a ?

2) How do you distinguish between an R12 or R134a installation.

3) If R12, how many 'o' rings are there to be changed to the new green type and where are they located ?

Look forward to any answers...

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Post by mat_fenwick » Tue Feb 07, 2006 10:08 am

Thanks for the comprehensive reply, my TX valve looks like the picture and he D shaped ring I thought I saw is in fact a D shaped copper tube, blanked off with solder at one end.

I have a supply of green O rings, there is one at every pipe union and I guess ideally you would change the ones in the compressor too.

I have been recommended R49 which I have been told is a drop in replacement for R12, turns out it is R134a which has been modified so that the old non PAG oils can be used. Has anyone any experience of this?

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Post by Vanny » Thu Feb 09, 2006 9:24 am

as best i know all the BX's use R12. Its only a case of draining the coolant, the PAG (lubricating) oil and changing the seals to swap to the R13, you can then buy or fit an adapter to the piping for easy recharge with the R13.


Theres a guy online who does all the parts you need to convert/regas yourself and its stupidly cheap. Better still i spent an hour on the phone to him the otherday and i can now totally rebuild and service mine for around £90 which is WAY cheaper than paying someoen else to do it!

www.carairconditioningsupplies.co.uk
or www.autokool.com


He's advised that as my aircon system has been U/S for quite some time and is sat in a box adsorbing water, that the dryer will be useless and can supply a new one for £50! Bonus!

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Post by AlanS » Thu Feb 09, 2006 9:46 am

Vanny wrote:

He's advised that as my aircon system has been U/S for quite some time and is sat in a box adsorbing water, that the dryer will be useless and can supply a new one for £50! Bonus!

The receiver dryer has almost to be changed every time the system is opened particularly in a wet climate, but I question his quoted price.
Most of them are made in Denmark by Danfoss and I can buy out here at A$60 whih is well below half the price you've been quoted.


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Post by Way2go » Thu Feb 09, 2006 7:37 pm

An aircon specialist locally has quoted £75 to service & recharge the aircon system on my BX. However if needs an R12 - R134a conversion that will be an extra £58-74.

As the system has not run recently, they say they also do a nitrogen fill & pressure test included within the service.

I guess as a one-off job there may not be any savings to be made by the diy approach, or is there? :?

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Post by AlanS » Thu Feb 09, 2006 9:32 pm

If it hasn't been charged with 134a previously, the problem is the O rings as they will eventually just rot and leak, so to not change them at conversion time is just putting off a job that will eventually have to be done. Difference is that when it leaks somewhere down the track, then you'll have to put up with all the usual bull of filling it with tracer dye etc which in the case of one of my sons car, ended up with more tracer dye than bloody gas in the system. It's a last resort way of tracing leaks anyway, not a fdront line attack as too many of these characters treat it.
The replacing of "O" rings is not oly a good DIY job, but a recommended one as an owner will often change the ones the guy doing the air/con will turn a blind eye to.
The receiver/dryer MUST be changed at a conversion due to the new gas requiring a different dessicant. If the T/X is needed, they can be bought as being suitable for R12 or R134a, so naturally you go the 134a way. If however, the R12 T/X is there, it will work OK on 134.
Look for oil stains around any connection, or anywhere on the air/con system; that's your clue to there being a gas leak and often these are found around places like the bellows of the t/X valve which means then that the T/X must be replaced.
The old story of operating a compressor every month or so is in reality a load of bull$hit. Over the years I've seen a few leak but the story about oil lubricating the seal and stopping it from drying out is a myth. Almost all compressor seals are not a rubber lip type as we know them in an automotive application; they are usually a couple of carbon and/or ceramic faces mated together under a spring pressure that requires a few bolts to clamp together. They are normally dry anyway, otherwise the gas would all leak out and the only ones I've ever seen that leaked have usually done so through incorrect fitting, a spot of dirt finding its way onto the mating surfaces or are worn out. Can you honestly imagine a lip seal holding back a pressure of say 150psi? Because on a hot day, sitting just above the road surface and if either not operating or when the car is parked, that kind of pressure and more is possible when the backpressure builds up due to heat. (Last weeks episode where I was in a Town where the outside temp showed 50 on my cars thermometer being a good case in point) and I had one car that hadn't had the air/con used for at least 5 years that didn't leak at the compressor, so that's more of an exception than a rule. If the seal happens to be stuffed, don't swallow that they can't be fixed. An hour, two at the most, just take your time and keep everything spotlessly clean.
If you DIY the T/X receibver dryer and "O" rings, don't leave the system open any more than necessary and if the repairer then wants to fluch it with nitro, evacuate and regas, that's about all that should be required to then get it all running.
I also have a write up on using a variable thermister to control the temperature much better than the original and the cost of the part is under A$1 and can be located to allow for easy future access and is best done whilst you are either converting or fitting the system and will save a days labour if needed to be done in the future.

Hope that fills in a few gaps.


Alan S
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