COLD AIR BUT SURGES WHEN DRIVING

[SpeedMetal]

Air is cold but motor surges while driving. Just replaced lines and compressor and updated to 134. got most of the old oil out but some remained in the condenser. I added 7oz of PAG, new compressor stated that it already had 3oz. I assumed that at least 1oz remained in the system. 7+3+1=11oz. at idle everything seems fine but feels like brake is dragging intermittently when driving at any speeds. makes a weird little squelch when engaging and feels like a substantial power draw. I put about 38oz of 134 into system.
Lets see if the wizards on this board can save me a trip to the big shop.
1970 c10 big block factory AC

Thanks for Your help!
-jeff[/color]

[bohica2xo]

OEM compressor was an A6. What did you replace the compressor with? Was anything else modified during the 134a conversion?

The original A6 / POA / TXV systems are usually very smooth. But they require good technical skills to convert them successfully to 134a

[SpeedMetal]

Reman Four Seasons A6 and got the new lines and 134 poa and exp valve from ClassicParts. I dont have good gauges but the free gauge on the refrigerant cans shows 48-22psi when kicks on/off. Truck sat for years and all freon was leaked out, decided to do update cuz R12 scarce in Cali. Im afraid of hydraulic'ing the new comp. Its my 16yo daughter's daily driver,...with 427 rat.
Thank you for Your time!

[Dougflas]

Did you use a POA elimination kit? A6 compressors were not meant to cycle on and off. GM tried that on some models and changed to the R4. R4 did not have an oil sump worth a damn so they were not a good choice. We will need high side pressures as well as low side pressures at 1500 RPM Reman'ed A6 from 4 seasons....good luck

[SpeedMetal]

Bought the late model tube style POA with pressure switch. Ive been screwin with the pressure adjusment but still get the cycling /surging at about 1000-1500rpm. Now 48-35 psi. Air plenty cold still. Seems backward that the pump cycles on when pressure gets high.

[Mr Bill]

Seems backward that the pump cycles on when pressure gets high.

Not weird at all, it's probably cycling off on LPCO at higher RPM's, so when it cycles off, the pressures equalize and rise, closing the LPCO and bringing the compressor back on. I would find me a decent set of gauges, and you might try temp. just bypassing the LPCO and see if it still cycles at higher RPM's if not, your either undercharged, or have the LPCO adjusted wrong.

[SpeedMetal]

Will Do!
Thanks for the tip and Your time!
-jeff