Packard Forum Index » Post-War (1946-54)

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Most MOPAR compressors from the '70s and early '80s V8 engines were dual pulley.

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That belt arrangement makes more sense but goes contrary to what you said in your first post. Granted it won't be NEEDED unless AC is on but the alternator WILL be running all the time with this belt arrangement-- but the compressor won't unless AC is on.

HH56: With a dual pulley groove arrangement like in the photo, are BOTH grooves being driven ONLY when the AC compressor clutch is engaged? or, does the dual pulley get driven all the time, and the clutch only disconnects or connects the compressor itself?

That is, when the compressor clutch is NOT engaging the compressor to run, is the alternator being driven by its belt or not?

Not a big deal if it IS being driven all the time, but less efficient.

Jim G

Dual pulley is just a single pulley with 2 grooves for 2 belts. It is driven off crankshaft and turns ALL the time but just freewheels. So for this application since the alt. is using the other groove, it will turn all the time the engine is running. When AC is turned on or when thermostat is cycling to regulate temp, the clutch magnetically engages the compressor crankshaft to the pulley but alternator is being driven before that action. Am not sure on a fully charged battery how much extra load the alternator will be. It will be turning but not being called on for much output--until the AC on & fan is on high, then that will pull approx 20-30amps.

Can someone with a regular 12 volt car with A/C measure how much current the clutch draws? Seems that 99% of the need for converting to 12 volta is the A/C clutch. Everyone seems happy with the rest of the car being 6 volts. shouldn't be too hard to design a power supply with a 6 volt input and a 12 volt output. Don't laugh yet.

I think most of the amp requirement is going to be the blower motor. If you'll check out Vintage Air schematics, on most there's a 30 amp circuit breaker directly to the blower speed control switch with some minor variations. In some 70-80's GM products, there was even a separate fused supply for high speed blower operation.

Here is a Sanden clutch spec sheet for a 12V dual groove assy. This is from their latest FLX7 modular series, and all clutches in this series ran 43-49 watts at 12V. Using the formula Amps = watts/volts the draw will be 3.5-4.08 amps. Even their older less efficient units probably won't go over 5.

There are commerical 6 to 12 volt converters available but most aren't geared to run more than a few amps for radio or tape deck type things. Largest one I saw doing a quick check was 8 amps.

EDIT: I did try to measure current but don't have the adapters here to complete circuit on dual pin plug on Ford and can't access the Dodge compressor without a lift. Also found a resistance value for Sanden clutch coils. Should have a resistance of 2.8-4.4 ohms. This also calculates out to max 4.5 amps at 12V.

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Does an air conditioning compressor clutch draw power:

1. ONLY when engaging or disengaging? or

2. All the time when engaged?

I'm trying to figure out how LONG that 5 amps is required - brief bursts or continuous for minutes at a time?

Jim G

Power draw is all the time while engaged. The duration will depend on what temp you have called for and how hot the ambient is. Watching the Ford cycle, with it about 90 degrees ambient, car temp set to what I think comfortable, the clutch was on about 30 seconds and off 10-15. On cooler days, it would be less on time and vice versa.

Also be aware that when a coil is energized there is a surge current for a few milliseconds that can be substantial, as well as an increase in voltage or back EMF when it's turned off. On older cars or basic systems with relay and switch logic it's not an issue. On newer cars or electronic systems these spikes are controlled by various means. Just be aware and take that into account if you're thinking of using anything solid state to run the clutch.

this is an old thread but here's a link to the 6/12 volt batteries. look under "products" then "cables and accessories"
www.antiqueautobattery.com

See pic in post #30 above. It's a slick idea but one potential problem. There is only ONE belt providing INITIAL driving power to BOTH AC pump AND alternator and maybe even water pump. No doubt the drive belt to the pump was originaly for generator. A LOT of load is placed on the belt by adding AC to it.

USUALY, the AC pumps are driven by ONE belt from the crank shaft. The alternator and water pump from a seperate belt.