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I'm rebuilding a 1972 Cutlass convertible and doing some mods/improvements to the the in the process. I want to wire the AC compressor to a dedicated switch like the newer cars, so I can used the AC in the defrost mode. The stock HVAC controls only engage the compressor in the AC & Max settings.
Here's my question, How much current does the AC compressor clutch draw when the AC is engaged? Can I wire the compressor directly to the ac dash switch or should I use a relay to handle more current? Thanks!
Rodney
... How much current does the AC compressor clutch draw when the AC is engaged? Can I wire the compressor directly to the ac dash switch or should I use a relay to handle more current?
If you look at the schematic in the CSM, you can see that the clutch is controlled by contacts in the dash switch assembly, so... Yes, you can control it without a realy.
I do not know the current draw of the clutch off the top of my head, but I believe it's about 1-2A.
The A/C clutch was switched in a number of different ways over the years, depending on model, and the modification you describe can make driving a bit more pleasant.
The stock '72 A/C control panel *does* engage the A/C clutch in Defrost. I've had 5 or so units, all did the same.
That's interesting, because I thought the same thing when I read this post, as I have had a number of GM cars with A/C over the years, and this has been the usual arrangement, but since I never had a '72, I checked the '72 CSM before I responded, and it clearly says that the compressor is not on in Defrost.
I was surprised, but I went with the manual. I find it interesting, but not that surprising, that your experience has been different. I wonder whether this is the sort of thing that would be credited to a mid-year engineering change, a documentation error, or something else.
Of course, to Rodney, the way to be sure is to remove your A/C controller from the dash (a great opportunity to disassemble, clean, and grease it ) and watch its operation as you slide through the settings - if the switch is designed to turn the compressor on in Defrost, it will be obvious.
I learned another new thing today; 70-71 Cutlass models w/AC did not engage the compressor in the defrost mode; but, 72 Cutlass models w/AC did engage the compressor in defrost mode. Here's a couple of pics to show the difference between the 2 model years.
The first pic is the AC-Heater control I was planning to use in my restoration. See the little tab between the Master switch (upper switch) and the compressor switch (lower switch)? It only engages in Normal & Max modes. The second pic I pulled off eBay. It has 2 little dowels that engage the compressor in Defrost, Normal & Max modes. The Master switch was moved to the bottom of the controller.
So I don't have to re-engineer my car just to engage the compressor in Defrost mode. Thanks Eric, you just saved me a bunch of work!
1970-71 Cutlass AC-Heater Controller
1972 Cutlass AC-Heater Controller
Last edited by cdrod; May 8, 2017 at 05:47 PM.
Reason: typos
Personally, I'd love to know the rationale for these changes, and for differences like these between models and Divisions, but I suspect they're buried in the sands of time.
) and watch its operation as you slide through the settings - if the switch is designed to turn the compressor on in Defrost, it will be obvious.
