Recently, I posted about my 240 (1991) pulsating at highway speeds. After tightening the ground for the relay, the pulsing was still present. Although I thought it was better, the drive back from work yesterday was noticeably worse than the day before: namely that the car was pulsing and struggling in lower gears.

Needless to say, I panicked about the transmission; however, when I turned the AC off, the car ran smoothly again. Then I did a road test. With the car going about 60mph, I turned on the AC and lo - the car pulsated. Once the AC was turned off, it was a perfectly smooth ride. I'll test again tomorrow, but now it appears that the OD is not the culprit.

If it is the AC, it would be great to know what about the AC is causing the problem. The AC system is too complex for me to work with, but it would at least be interesting. The only maintenance that has been done to the AC, to my knowledge, is that it was recharged 2 years ago. What would cause the car to struggle so badly with the AC on? I know the AC is parasitic but dragging the car down that much seems unusual. Could it have something to do with the compressor? Or could it be wiring? My imagination...? (:

Thank you for your assistance!

Cordially,
Katherine
1991 Volvo 240 Sedan, 126K