1993 E350 Club Wagon R12 to R134a

:banghead: I just finished converting my A/C system from R12 to R134. I sucked it down to a good vacuum and held it for at least 20 - 30 minutes, then shot the system with a good brand of R134 that included oil and leak seal ( just in case). I have a R134 gauge set but I am having trouble understanding the results. I have ice cold (or nearly) air in the back of the van, but the front air is mediocre at best.

I am reading about 37 to 42 lbs on the suction and about 180 on the high side. It seems to me that the compressor should be cycling but the compressor seems to just stay on all the time. On top of that I believe that these pressures are too high but I can't find any good reference materials on the R12 to R134 conversion. If I leave it run at idle the low and high side pressures eventually creep up to about 45 on suction and as much as 230 on high side.

Both heat exchangers seem to have plenty of condensation dripping from them, I am using a box fan on high speed in front of the condenser to simulate driving speeds for incoming air. Although this is a 93, it is in really mint condition mechanically - only 64,000 original miles on the clock. When I cut the vehicle off I notice that it only takes a few seconds for the suction side pressure and high side to equalize at about 90 lbs. Shouldn't there be an internal check valve system or something that would prevent such a quick equalization? Pressures were taken with both the front and rear units on high fan speeds.

Could it just be the excessive heat build up in the vicinity of the front unit because the vehicle is sitting still (despite the box fan?). What should normal pressures be after a conversion? How many ounces would be a correct shot for this system? Anybody else done this conversion?

You sound a little lost. The pressure in the system changes with ambient temperature, the hotter it is outside the higher the pressure. As your A/C runs and gets cooler the pressure of the low side should get lower and the pressure on the high side should get higher. When you did the convertion did you drain the old oil? If not you should have. Once the system hits an all time low in pressure on the low side it should not rise unless the compressor starts cycling off. It sounds like you may have a gummed up front orifice tube.


:banghead: I just finished converting my A/C system from R12 to R134. I sucked it down to a good vacuum and held it for at least 20 - 30 minutes, then shot the system with a good brand of R134 that included oil and leak seal ( just in case). I have a R134 gauge set but I am having trouble understanding the results. I have ice cold (or nearly) air in the back of the van, but the front air is mediocre at best.

I am reading about 37 to 42 lbs on the suction and about 180 on the high side. It seems to me that the compressor should be cycling but the compressor seems to just stay on all the time. On top of that I believe that these pressures are too high but I can't find any good reference materials on the R12 to R134 conversion. If I leave it run at idle the low and high side pressures eventually creep up to about 45 on suction and as much as 230 on high side.

Both heat exchangers seem to have plenty of condensation dripping from them, I am using a box fan on high speed in front of the condenser to simulate driving speeds for incoming air. Although this is a 93, it is in really mint condition mechanically - only 64,000 original miles on the clock. When I cut the vehicle off I notice that it only takes a few seconds for the suction side pressure and high side to equalize at about 90 lbs. Shouldn't there be an internal check valve system or something that would prevent such a quick equalization? Pressures were taken with both the front and rear units on high fan speeds.

Could it just be the excessive heat build up in the vicinity of the front unit because the vehicle is sitting still (despite the box fan?). What should normal pressures be after a conversion? How many ounces would be a correct shot for this system? Anybody else done this conversion?

Nope - I did not drain the old oil - so two questions - where is the appropriate drain point for the system oil (besides just picking a low point on the condenser) and I have pretty much traced out all the lines and have yet to figure out where these orifice tubes are located. Is it reasonable to assume that both the front and rear lines would have individual orifice tubes even though they use the same compressor? If there is only one for the entire system then why would the rear be good and cold but the front be so-so?

Also - and I'm not giving in to pride here - but I am not THAT confused about pressure / temperature relationships. The "Old Nuke ET" name comes from 9 years operating a reactor on a sub...

Thanks for any help you can give.

Most of the system oil sits in your Accumulator/Drier. Its always best to remove the accumulator and drian the oil that was in there and replace the same amount of oil that came out of there. Too much oil is no good. Most times the accumulator is cheap enough just to replace. The system should be flushed with a/c system flush solvent to get all of the old oil out of it.

Your van has one orifice tube that is located in the front evaporator core inlet tube. I'm not 100% sure but I think that ford uses an expansion valve instead on the rear. I know that GM only uses one orifice for their rear a/c systems on their yukon. so having just one on a dual system is normal. With the use of only one orifice tube the rear would work better because the orifice tube is located at the front evaporator core inlet tube, if it is dirty it will restrict flow going to your front evaporator.

As for charging the system, This is to give you an idea of the charge pressure needed on the low side.

Ambient Temp vs PSI

65F 25-35PSI
70F 35-40PSI
75F 35-45PSI
80F 40-50PSI
85-90F 45-55PSI
95-110F 50-55PSI

Do not ever charge.

Hope this helps.


Nope - I did not drain the old oil - so two questions - where is the appropriate drain point for the system oil (besides just picking a low point on the condenser) and I have pretty much traced out all the lines and have yet to figure out where these orifice tubes are located. Is it reasonable to assume that both the front and rear lines would have individual orifice tubes even though they use the same compressor? If there is only one for the entire system then why would the rear be good and cold but the front be so-so?

Also - and I'm not giving in to pride here - but I am not THAT confused about pressure / temperature relationships. The "Old Nuke ET" name comes from 9 years operating a reactor on a sub...

Thanks for any help you can give