Trying to get the air-con working.

[bx petrol auto saloon]

Dear Vanny,
Firstly, thank-you so very much for your very kind reply Vanny
Secondly, I fully understand what you are asking and tomorrow I will get my test light out and see if I have a live at the block connector right next to the compressor, I have already taken that connector apart yesterday to clean and lub the terminals. And I will report back when I do that Vanny
Thank-you very much indeed
Vince,

[bx petrol auto saloon]

Dear W2G,
Firstly, thank-you for your very very kind replies
Secondly, I realised yesterday when I was fiddling about with the potentiometer, when the air-con relay started working and the twin fans at the front, that they appeared to be ignition fed. I am giving the potentiometer the benefit of the doubt at the moment The good thing about getting the air-con relay and the fans working is I have a new toy to play with now
Thirdly, I have just now been out and had a shufty around the air-con system under her bonnet, and I have noticed a small circular type pressure switchy looking thing that is connected to the drier receiver, it has a small electrical block connector attatched to it and it is located behind the n/s headlamp in front of the air filter housing Are you saying that this may be faulty and may be not allowing the system to work correctly Tomorrow I will check it for a feed aswell, and have a play around with it etc.
Thank-you so very much for all of your very kind advice and help
Vince,

[bx petrol auto saloon]

Dear Mat,
Firstly, thank-you so very much Mat for your very kind replies
Secondly, thank-you for kindly advising me on the type of potentiometer at least I may be to find another one at some point in the future
Thirdly, thank-you for kindly looking for one for me Mat to me it was seeming as if the point at which it broke, the plug had just fallen off at the back, and I had pulled the plug out of the way so it wasn,t causing a problem getting the circuit board back in, when it all went a bit difficult going back in around where the spade connectors come out of the back of the white plastic housing
Many thanks Mat
Vince,

[mat_fenwick]

small circular type pressure switchy looking thing that is connected to the drier receiver, it has a small electrical block connector attatched to it

If you want to test the function of the rest of the system, i.e. by replicating the action of this pressure switch, there are two things you can do.

On the four way connector, short out terminals 1 and 2. This is the signal for correct pressure in the system. If the compressor clutch now cuts in, either the system pressure is truly low, or the pressure switch is falsely indicating low pressure. If you short out terminals 3 and 4, this is the signal for high pressure, so the radiator fan(s) should rotate at full speed.

[Vanny]

/\ As I understand it that is not all. R12 is quite a high pressure system and as such has a pressure microswitch in the system to detect when the gas pressure falls below a threshold. The purpose of this is so the clutch does not engage when the pressure is low and hence damage the pump by making it potentially run dry.
The alternative refrigerants I believe are not such high pressure as R12 and IIRC there may be an issue then requiring a change of this pressure switch.

So ........ switching the system on does not mean you will get power to the clutch if the refrigerant is no longer fully charged irrespective of a hiss from a quick tap on the schrader valve?

But how does the system know it's low on pressure if the compressor never turns? My understanding of this simple system is that it will fire up for a short time regardless of what the sensor sees initially. Could be wrong mind but I thought the pressure switch is to ensure a minimum and maximum operating pressure rather than charge pressure.

[Way2go]

But how does the system know it's low on pressure if the compressor never turns? My understanding of this simple system is that it will fire up for a short time regardless of what the sensor sees initially. Could be wrong mind but I thought the pressure switch is to ensure a minimum and maximum operating pressure rather than charge pressure.

My BX needs its AC charging. I have also had AC on Saabs and Volvo's & on none of these does the AC compressor kick in at all when gas pressure is low, presumably to protect the system until action is taken.

The BX is a simple system but is equipped with "relay logic" to control the system from the few electrical sensors that it does possess. The high side sensor will by virtue of the relays give information on both low and high operating pressures but the dedicated low sensor I would think would be primarily to detect residual charge pressure.

[Jaba]

But how does the system know it's low on pressure if the compressor never turns? My understanding of this simple system is that it will fire up for a short time regardless of what the sensor sees initially. Could be wrong mind but I thought the pressure switch is to ensure a minimum and maximum operating pressure rather than charge pressure.

Its a simple inline pressure switch. On a charged system which does work there is always a residual pressure (>36psi) in the system with the compressor off and this is what is effectively being measured and enables the compressor to kick in or not as the case may be when it is switched on by the cool BX fanatic in the car.
The high pressure switch has an additional contact on factory aircon systems for a medium pressure connection when the fans will run at high speed and the compressor is left running. Unlike the full high pressure switch which cuts out the compressor and just runs the HSFs.

[Vanny]

Fair enough, i think my understanding is a little skewed by variable displacement compressor logic which works rather differently to fixed displacement compressors, in my mind at least.

[bx petrol auto saloon]

Dear Jaba,
Firstly thank-you so much indeed for your very very kind reply
Secondly please excuse my late reply , Today I went out to do a few checks on her air-con sytem. I tried to get the pressure of the air-con system, but unfortunately my tyre pressure gauge doesn,t fit onto the valves, as they appear to be a tiny tad larger than normal type of tyre valve. I thought it would be great if I could get a pressure reading from the system
Is there any way I can do this ? or is this specialised equipment
Many Thanks Jaba for all of your kind advice
Vince,

[bx petrol auto saloon]

Dear All,
Today, I managed to carry out a few vital checks on her air-con sytem. I tested the two wire plug at the compressor, which has no lives at all ( I tried it with the ignition on and also with air-con switch switched on and both fans on aswell and the engine running aswell )
I also checked for lives at the four pin wiring connector on the electric valve by the air filter assembly ( Only no 3 pin connector has a live ) all the others are nothing.
I also tried to bridge no 1 and no 2 pin to get the air-con clutch to cut in, but to no avail. I also tried to bridge no 3 and no 4 pins in order to get the fans working at full speed, but no avail. I did these tests with the engine running on idle and with the air-con button switched on aswell
Could the above results, may be the electric valve by the air filter not working very well
Many thanks indeed to everyone for all of your very very kind and invalueable advice and help
Vince,

[BX Bandit]

My BX needs its AC charging........

What do you charge yours up with? Is it a drop in replacement or have to converted?

[Jaba]

Fair enough, i think my understanding is a little skewed by variable displacement compressor logic which works rather differently to fixed displacement compressors, in my mind at least.

Err, yes, that's logical Vanny

[Way2go]

My BX needs its AC charging........

What do you charge yours up with? Is it a drop in replacement or have to converted?

Its still R12 in my system so after some quotes for the conversion to R134a, I decided to leave it be until I was ready to do the conversion myself. I bought a new receiver/dryer in readiness but still need to get the rest like the green 'o' rings, pipe connectors & PAG Oil. After that outlay I guess its then to the recharge station for about £70.

To be honest we haven't had the recent summers to miss it. Its been missed more in the winters because it was ace at immediately demisting the screens before setting off.

[Vanny]

After that outlay I guess its then to the recharge station for about £70.

Make sure you warn the garage/tech that it has R12 in when you book the work. A lot of places won't touch R12 because they don't have the facilities to dispose of it.

And if you can afford it and find it then ND8 is the dogs dangly bits of PAG oil. Or better still ND12!

[Jaba]

I put mineral and pag oil and R134a compatible ester oil in mine when I did the conversion as I thought that this would mix with the small amount of mineral oil that will be left in the system.
Then when it needs a recharge I will let them put pag oil in as this will mix with the ester oil.