Re: Aftermarket Air Conditioning

Posted by DavidPackard On 2021/9/4 17:22:28

Marc Williams

I finally had a chance to measure the coil resistance on the A/C compressor on my ’54 Cavalier. What I found was 3.6 ohms, which is exactly the same as the coil in a replacement compressor I just bought for my ’99 Suburban.

I also went on the fruitless task of searching the web for an A/C clutch designed for 6 volts, meaning one half of the resistance to hold the same current. Just like many before me I failed miserably, however I did find that coils come in ‘one-wire’ and ‘two-wire’ configurations. All are actually ‘two-wire’, and it’s just a distinction on whether the ‘ground’ wire is external or terminated on the case of the compressor. I also found a few sites that mentioned a 12 volt coil will work on a 6 volt car, but speculated that there might be cases where the clutch did not function properly at 6 volts. There was a discussion that at the normal system voltage of about 7 volts the success rate would be better.

There was also a discussion about shimming the solenoid air gap to the minimum allowable. The specification for air gap for a Sanden compressors is typically 0.016 to 0.031 inch, but that value varies with air compressor manufacturer and compressor model. The air gap on my Sanden equipped ’54 Cavalier is 0.025 inch, so there is a bit of margin I could take advantage of if my compressor had problems with ‘pull-in’.

My take a ways are:
1. The resistance of a modern air conditioner clutch coil is approximately 3.6 ohms, and at that resistance success on 6 volts is not guaranteed, but is highly likely.
2. Modern air conditioner compressors are available in either a ‘one-wire’ or ‘two-wire’ clutch configurations, and the installation should provide a clutch coil ground path that has the least practical resistance.
3. Reducing the clutch air gap to the specification minimum would help, but that adjustment may not be required on all compressor clutches that will be operated at 6 volts.

dp