Truck is in my sig, and I've only had it for a few weeks.

When the AC is on (that's right, SoCal has needed AC this year already. Neener), the clutch cycles every 15-20 seconds. The system blows ice cold (probably still the good ol' R-12) and there are no other issues, but I'm just wondering if this is normal. I know my old 89 with a 351W kinda did the same thing, though I don't recall it being as frequent. Is this a sign that the system has an issue, or is it perfectly normal? My theory is that perhaps the charge is low and the clutch keeps engaging to keep the pressure up?

Thanks!

Mike

 

You are half right.
You are low on R-12 but it is cycling off the low pressure switch.
When the low side drops below the cutout pressure it turn the compressor off.
With the compressor off the low side pressure comes back up to the cut in pressure and the compressor comes back on.

 

So, sounds like a system purge and some fresh R134 (done by a shop, of course) is the right way to go.

Mike

 

If you can find a shop to recharge it with r12 I'd rather go that route.
It is low on charge. But most people on here will say you need a new pump and accumulator and orings when you convert to 134a.
As long as the shop don't rip you off, I say r12.
They usually charge you a flat fee, then by the pound. And hopefully they don't charge you what goes in the system, and only what they need to add. (they are gonna suck out at least half what goes in it) It get expensive quick when they forget they pulled out a pound or so.

 

Sometimes an overcharge will cause this, as the high side pressure increases faster with more in the system. High pressure cut-off switch shuts down the compressor to keep things in check.

You'll need new hoses (barrier hoses), seals compatible with PAG oil, and the appropriate compressor if you switch to R134A. R409-A is as close as you can get to R12 as far as operating pressures and component compatibility.

FWIW you'll be spending a lot on R12, since it is illegal to manufacture. Virgin refrigerant can cost a shop $1500 for a 20lb container. Recycled can be slightly cheaper, and has higher SAE purity standards.