Automotive Air Conditioning Information Forum

Kindly post the year, make, model, engine size, and mileage for your vehicle. Is this a US-spec or non-US-spec vehicle?


My question is regarding constantly running ac compressors.
Your topic says, in part: "...re constantly running ac compressors." And your post above states essentially the same ...

grumpy old man wrote: Mon Mar 30, 2026 2:18 pm ...I think it is classic air. Had I known about them I would have gone that route but 20 20 vision is only hindsight.

My thought, too. There are a few of those companies around: Classic Auto Air, Old Air Products, Vintage Air, et al. .

I got it in the available space but with all the ductwork I needed to manufacture with the fan in high it has the air flow of the average unit with the fan speed on 2 of 4. All the twists and turns cause so much restriction that I need a much more powerful fan.
Have you tried larger-diameter ...

The under-hood decal always takes precedence over the manufacturer-published specs. That makes it 1.35 pounds times 16 ounces, resulting in 21.6 ounces net weight of R-134a.

The UV dye, added sparingly, won't hurt anything.

On the decal, does it specify what viscosity of oil your system takes? PAG ...

I also wanted to add there is a rattling noise with compressor running.
A rattling noise when the compressor runs usually indicates that the refrigerant charge is "off"—either undercharged or overcharged—and/or something is wrong internally. Since it's the original compressor with ~156,000 miles ...

Right off the bat, it sounds like the refrigerant leaked out, although I can't explain the clutch still being engaged. (Maybe it's stuck "on"?)

Leaks under pressure can happen even though the system holds vacuum.

When you say extra clicks, do they sound like the clutch disengaging and engaging, or ...

James, The first thing I would check is the amount of refrigerant in the system. It could be something else, but let's start there.

What is the make, model, year, and mileage of your vehicle?

I can't speak for GM Tech . As for the plastic caps withstanding 300+ PSI in MVAC systems, they are indeed intended to withstand such high pressures. In fact, the robust threaded design of the caps is sufficient for more than 400 PSI on the high side. Otherwise, most trinary (safety) switches wouldn ...

I'm not an MVAC designer, but I'm guessing that trinary switch settings would depend on the design engineer working on a particular system.

If I recall correctly, trinary switch pressures are typically set to the following limits: Low-pressure cutoff at ~30 PSI; high-pressure cutoff at ~400 PSI ...

Caps designed for a tire valve and for a Mobile Vehicle Air Conditioning system's access ports are different, as are the pressures, which has been correctly pointed out. On an MVAC system, the caps are the primary seals while the Schrader valves are the secondary seals.