BX Air conditioning R134A conversion (all you need to know thread)

[Dragon Man]

Hello, i decided to make a thread on the BX's aircon system specs:

disclaimer, air conditioning systems must only be serviced by licensed personnel. strict laws are in force in the UK regarding the use of refrigeration gasses to be evacuated/filled ONLY by a licensed person(s)/company!
that said, you can do whatever work you want on a already completely evacuated system so long as you do not fill the system yourself (unless licensed).

on to the topic in hand,

Capacities:

the Diesel BX takes 800 grams of R12 refrigerant, and 135ml of Suniso 5GS oil.
the petrol 1.9 GTi 16V (with XU9J4 engine) uses 800 grams of R12 refrigerant and 135ml of Suniso 5GS oil.
other petrol BX's take 1000 grams of R12 refrigerant and 135ml of Suniso 5GS oil.

Oil:

the oil used in the Citroen BX air conditioning system only works with R12 refrigerant so it does need to be changed. normally there is a drain port on compressors but sometimes not. the only way to remove the old oil is to remove the compressor and let the oil drain out of the high or low pressure connectors.

PAO 68 is the oil i would replace the original oil with. this PDF (http://www.behrhellaservice.com/behr-he ... BHS_EN.pdf) has some great info on this oil kind. stating that PAO 68 is an oil that can be mixed with the other oils with no ill effect.
(note that *some* oils in AC systems when doing the R12 to R134A conversion can go acidic if old oil of a different kind is left behind! so the whole system has to be flushed. thankfully with our system, using PAO 68 oil with trace amounts of the original oil, we can get away with this! )

Seals:

next thing to do is change your O ring seals. now you dont have to do this, but given the fact that these are going to be about 20 years old now, and the fact that the R134A molecule is smaller than the R12 molecule it is a good idea to change these.

theres a few kinds of "rubber" you can use, "Nitrile" is one that is used for refrigeration. the one that has the more longer life is called "Neoprene" which can withstand the oil and refrigerant for many years. another is "perfluoroelastomer" seals. these may be hard to find but again fully survive R134A refrigeration.

Replaceables:

replacing the dryer/accumulator is optional, but highly recommended. if you do not change the dryer/accumulator the whole system should be held under a vacuum for a few days to make sure that everything that can turn into a gas - like water is removed(boiled off and turned into atmosphere that can be vacuumed out again later on before being filled with refrigerant). even water being held in the desiccant inside the Dryer/Accumulator can be sucked out to some extent when held under vacuum for long periods of time. the longer the better. this also allows you to check to see if theres any leaks in the system too - if it cant hold a vacuum, it cant hold refrigerant.

if you do replace the dryer/accumulator, it is recommended that you hold the system under a vacuum for a minimum of 45 minuets. then vacuum again.

Pipes:

all original BX air conditioning piping and evaporator/condenser will be fine with the new refrigerant so long as ware and over charging does not occur.

R12 to R134A conversion ratios:

now because of R134A being a higher pressure gas you only need to use 80-85% of the original R12 charge. (say 80% for safe measure)

say we are going to use the 80% ratio,
with BX's using 800 grams of R12, it would only need 640 grams of R134A charge.
with BX's using 1000 grams of R12, it would only need 800 grams of R134A charge.


Feel free to add to this, this is all info that i have gathered doing my own research (and some experience from working in a garage)

i hope this helps someone in the future.

[JayW]

strict laws are in force in the UK regarding the use of refrigeration gasses to be evacuated/filled ONLY by a licensed person(s)/company.

I can't comment on anything else as it's not my speciality, but the above statement is wrong. There is no such law, this is why I can regularly nip to Halfords and buy a can of gas to refill various cars. This I know, because I do.

[Dragon Man]

theres no law on buying a canister filed with the R134A refrigerant, however to fill or evacuate a system though you do need to be qualified to handle F gasses.

the buying of R134A from halfords is a loophole. note that you can return the empty canister and get a slight refund. i do not know the details fully but it is along those lines. my brother works at a local halfords and with both my brother and I having a keen interest in refrigeration technology, we found it funny that halfords actually managed to sell the said gas in a legal manner.

the laws are on the gov.uk website. (https://www.gov.uk/guidance/f-gas-requi ... echnicians)

its funny as it also words it to make it against the law (holding you accountable) should your vehicles air conditioning system ever vent to atmosphere due to lack of service. which is about every person with an older car that has needed the AC re-gassing.

personally if you ask me its a 1% caring for the environment and 99% profit making thing.

[senmathal]

Thanks for this thread!

I planning for this job in the future, maybe next summer. I bought a 16 Valve recently and the car was fitted with AC but the condenser was missing. I tested the compressor by short cut in the pressure switch. No unusual noise and some air was coming out of the pipe so I hope it´s OK. Perhaps I have to change the shaft seal. I planning to fit a new condenser and dryer.

One thing I wonder is if the O-rings for the evaporator is inside the car or in the engine compartment. My car is under some snow here i the north of Sweden so it is a little difficult to look for it I´m a little bit afraid the pipe connections are under the dashboard

/Mats

[Jaba]

Thanks for this thread!

One thing I wonder is if the O-rings for the evaporator is inside the car or in the engine compartment. My car is under some snow here i the north of Sweden so it is a little difficult to look for it I´m a little bit afraid the pipe connections are under the dashboard

The evaporator orings- 4 in all are on both sides of the expansion valve which is mounted on the LH side of the central part of the dash. They are accessible if you are flexible enough, just follow the hoses. The steering column on LH drive might make it more tricky. Then depending on the set up there are also usually 2 seals in the engine compartment where the aircon hoses enter the bulkhead. So that makes 6 in all, 3 each of the two different sizes.

[senmathal]

Thank you for the answer.

It seems that the engine radiator is different on BX 16 Valve with AC? Do you know what is different? I´m afraid that the radiator has been replaced and that this is the reason why the condenser is taken away.

/Mats

[Vanny]

For the seals, Citroen carry a generic kit for all older vehicles, costs around £12 and covers all the seals you need and plenty of spares.

It is good practise to replace seals every time you uncouple a pipe as this is normally when they get damaged.

R12 to R134A conversion ratios:

now because of R134A being a higher pressure gas you only need to use 80-85% of the original R12 charge. (say 80% for safe measure)

say we are going to use the 80% ratio,
with BX's using 800 grams of R12, it would only need 640 grams of R134A charge.
with BX's using 1000 grams of R12, it would only need 800 grams of R134A charge.

I'm not sure where the data for this statement has come from, but I don't agree.

Pressure is generated by the compressor (pump) and released by the thermal expansion valve. The TXV releases pressure to maintain a constant expanding flow of refrigerant across the evaporator surface. The control and feedback pressures are set by a spring in the TXV and the strength of this spring is called the tonnage. As you wont be changing this, the optimum operating pressure of the gas is irrelevant.

The performance of R134a is generally comparable to R12. The correct charge weight is determined by soaking the car in a 40 to 45c ambient then turning on the AC and timing how long it takes to pull the cabin down. You repeat this until you find the optimum charge/pull down rate, takes a couple of days and I doubt any one here would bother.

[Dragon Man]

this is true, but so i have been told it is the best way if pressures are not originally known.

hmm.. how about this?

if anyone on here is still running an original R12 charge, could the system have a set of gauges hooked up to it to read the pressure the pump gives out?

it would be nice if there was some kind of R12 to R134A calculator which compensated for the different gas loads/pressures

[senmathal]

Have got my BX AC filled with R134a recently an it works perfect. When I bought my car the condenser was missing and hav been missing for some years. The one I bought the car from did not know there have been AC in the car. The information in this tread was very helpful for me.

What I have done is mounting a new condenser, new dry filter and a new expansion valve. All O-rings was replaced and the compressor was drained on old oil. Then I filled 120 ml new ester oil and took the car to the workshop where it was filled with 800 gram R134a. Everything worked perfects directly. An the first hot summer days in Sweden arrived just now. Nice to drive a cold BX.

/Mats

[Dragon Man]

glad this helped you out! i have just cleaned the AC radiator with some "outdoor AC condenser cleaner" which is like a foam spray (like shaving foam) that covers the coil, then you just wash it off with a hose pipe after a few mins of letting it soak. it has cleaned out my AC really good! check this out...

dirty:


clean:


product:

[senmathal]

I observed that the high speed mode on the condenser fans not activates. Is it normal that the presssure don´t come up to the level needed to activate the high speed mode. It´s not very hot here in Sweden. Around 17°C

The cooling is still good and with the engine at idle and the coupe fan at low speed the compressor only run fore a short time, maybe 30 sec and then stop for up to a minut or so. But with the coupe fan at high speed the compressor works constantly.

I have replaced the pressure contakt with a new one. Can I have lost some gas or did it work as it should?

/Mats

[Jaba]

Bit confused here a you say the high speed mode does not activate then later you say that when it does run at high speed then the compressor runs continuallly.
I rarely see or hear high speed mode for the A/C it only comes on when the pressure is above 19bar, normal pressure is > 2.5bar. At very high pressure >26bar the compressor should be off and high speed on.
The fans are only there to get rid of excess heat. So as long the cooled air is 5 to 10 degrees you do not have a problem. In other words they could be left off altogether while the car is moving.

[Way2go]

Bit confused here too, are you confusing cooling fans with blower motors? The rad cooling fans will come on at low speed when the a/c switch is set to on. They will only go to high speed when triggered by the high temperature switch of rad temperature?

Jaba, the BX can take air from outside or can recirc. Blowers must come on in recirc mode whether or not the car is moving.

[senmathal]

Thanks for answering and sorry for my bad English, Way2go is right, I use the wrong word for the blower motor. When I say "coupe fan" I mean the blower motor. So what I say is that the compressor runs continually when the blower motor is set at full speed.

As Jaba says the high speed will come on when the pressure is above 19 bar and do so if I short circuit the pressure switch pin 3 and 4.

But as I understand it is no need to worry. I thought the high speed should come on more often.

/Mats

[Dragon Man]

sounds odd the system may be over or under charged. it may also be an issue with the blower speed controller. i have yet to fix mine. when i put mine on max speed the blower turns off :/