1978 460cui with A/C

I a have 1978 clubwagon E-250 with the 460 and dual zone A/C. What is involved in retrofitting the A/C with 134a refrigerant?

Is the valve on the curved tube just to the right of the compressor the low pressure fitting, or a high pressure fitting?

Reply to
Steph
Loading thread data ...

Large Hose going into aluminum accumulator is the low side pressure fitting. Smaller Hose with smaller pressure fitting is the high side.

Retrofitting the air conditioner will require changing the oil in the compressor case, for best results do a nitrogen purge on the system to remove any residual r-12 remnants. I usually replace the compressor due to age and not having to crack the system back open again. The thermostatic expansion valve (TXV) or metering tube will have to be replaced due to different pressure tolerances between R-12 and R-134a. I would also replace ALL of the rubber o-rings while the system is depressurized. Lastly pull a vacuum on the system, I usually leave the vacuum pump running for about 30 minutes. Check for leaks by stopping the vacuum pump and closing all valves. If the vacuum does not drop at all after 5 minutes, you are ready to charge the system, make sure you purge the air from the hose lines. Don't forget to install the retrofit low side fittings before pulling the vacuum.

As far as the fitting on the tube, you must compare fitting sizes the larger one is the high side.

Any questions, email me direct, just remove the extra dot com.

TM

Reply to
TM

This is a wasted effort, a good vacum will remove it.

THe p[roblem with this is that it changes the flow rate and prusse curve for compressor if you change orfice size. All though the logic is good, the possible side effects are not.

Another danger here is that R134a is not compatable with mineral oil so some extra PAG oil has to be added to system to bind mineral oil to pag and pag to R134a to move it through system and it can reduce cooling some if too much is added and increase head pressure and reduce compressor life too. ALso given age of vehcile, you should replace recv/dryer and precharge it with PAG as this will let you ad PAG to system without over charging it with oil

When this is all said and done, there will be a lose of cooling capacity because R134a has about 16% less heat capacity than R12 when it is expanded and cooled. R134a systems have larger condensors and evapotars and different compressors and flow rates to help minimize this effect but a lot of time R134 is a R12 systems can provide marginal results especailly if system was not the great on R12 to begin with.

----------------- The SnoMan

formatting link

Reply to
SnoMan

Just how many retrofits have you done Mr Sno Man? I have over 100 under my belt with a less than 5% failure rate. 90% of the failures are a result of marginal parts not being replaced according to my recommendation.

Additional information embedded.

Only if the system has been sealed, hasn't leaked down or succumbed to compressor failure.

The manufacturer of the refrigerant and automobile manufacturers recommend changing the orifice tube. Thereagain, how many retrofits do you have under your belt? I will not waste my time going into specific weights and solubility and long term longevity should best practices not be observed. Sure you can cut corners if you are short on cash, but it will be more costly in the long run.

That was addressed with the changing of the oil. By the given age of the vehicle I would replace the compressor as a matter of principle if it has never been replaced. Compressor manufacturer warranties require you to change the accumulator/receiver/dryer or the warranty is void.

That is precisely the reason the TXV/orifice tube must be replaced or your results will be horrid at idle.

There should be two orifice tubes or TXV's on this particular vehicle according to the service manual more likely the latter.

Reply to
TM

I would not brag about a 5% failure rate, 0% is a lot more impressive. When you change the flow rate as you suggest, with a larger orfice for R134 you change pressure curve and drop accross it since compressor is the same. Using R134 is a R12 system is a bandaid fix at best and there are other options out there that will cool better than R134 in a R12 system and do not require different oil because of incompatabilty with mineral oil like R134 is. Nothing is gained with your purge except maybe something to charge for if you do it for a fee. You could purge it with air if you really feel the need to since it is 79% nitrogen anyway. A good vacum held for a while will remove old freon and moisture but I would change recv/dryer which shold be done here which you fail to mention which casts doubt on your methods. Besides, you do know that R134a is VERY poisonous and that it too will be banned in 2012 too? Replace a banned refrigerant with another soon to be banned one (that is inferior in performance to in a R12 system), Not very wise. Also PAG oil is glycol based so corrosion is a bigger potenail problem in a converter R12 system and that is why you change the drier. (mineral oil in R12 system does not react much with moistur (not like R134a and PAG oil does anyway)

----------------- The SnoMan

formatting link

Reply to
SnoMan

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.