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I just bought a 92 SC400 that needed the AC charged. The shop I went to recommended converting the AC to r134 due to r12 cost. I had that done and everything was working fine when I left the shop. While I was driving home I noticed a low bass hit that sounded like the compressor skipping. The skip would happen about every two minutes, but when it it did skip, it would skip 1-3 times in a row. When I got home, I left the car in idle and checked the compressor and it was fine. I stood around the car and noticed that the sound was coming from the exhausts as if the engine was misfiring. I'm thinking maybe I need new spark plugs, but I'm not sure. Is anyone experienced with this problem. The car only does this when the AC is on. Thanks for any help.

RPH74

If you didn't have this problem before you had your A/C converted, it would seem hard to believe that your plugs suddenly went bad. What did the shop replace when you converted to r134a? Does it blow cold? Does the misfire hit when the A/C is off? When you are checking the compressor at idle, do you have it at FULL blast-max cold and max fan? Otherwise, the compressor may shut itself off.
I did the r134a conversion on my 91 Eclipse, and it would do the same thing (misfire and smoke) after I vented some of the r134a from the system, after I overfilled it a little. So could you possibly have a refrigerant leak?

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I bought the car last Friday and at the time it would blow some what cold air only when in the evening when the sun wasn't out. Before the conversion I never kept the AC on long enough to notice anything wrong. The engine misfires mainly when the AC is at full blast and decreases in rate when the AC is turned down. The AC does blow cold air now. According to the shop I went to, they said I didn't have any leaks. I checked the compressor when the AC was at max and it never misfires when the AC is off.

RPH74

Well, it sounds like it's got to be related to the A/C system. Was it a reputable shop? I would take it back to the shop and ask for advice. The reason I mention that is because many shops are pushing for r-134a conversions, because it is more $$ in their pockets. If your system was not leaking, they should have simply added more R-12. R-12 has actually gone down in price as of late because of lower demand ( any car using R-12 is now 10 years or older!) I was able to buy a can last week of R-12 for $25 to top off my SC300!! All I had to do was get my 609 A/C tech license online for $15.
Hopefully they put in enough oil, so that the compressor does not blow itself up. Do you know if they used POE (Polyol Ester) oil or PAG oil? They should have used POE for the retrofit. PAG just doesn't cut it with retrofits very well, because it does not react well with the chloride ions left behind from the original R-12 system. You may try going to Wal-Mart and buying the 2 ounce can of POE oil for $3.49 (you will also need a r134a can tap which Wal=Mart sells) and see if anything improves-make sure you add it to the LOW side port, which I'm not sure where it is, since I have the SC300. You will find that the connector will only fit on the low side port anyway, so you shouldn't get confused. That would only apply if it is the compressor making the noise. It's hard for me to link A/C causing misfire, unless there is a bad refrigerant leak, since the A/C is a closed system, and the only correlation to the rest of the car is a little extra work on the motor to drive the compressor. Listen a little closer to make sure it is not the compressor making the noise, and see in a couple of days if your A/C still blows cold to make sure there wasn't a bad leak causing the misfire.

p.hase

i had the same misfiring and dropouts when using the A/C. i changed the spark plugs and its gone. somehow it must be engery consuming.