I've just purchased a very clean, low mileage 2003 aviator awd, with a very poorly functioning air conditioner. I'm likely going to put it into a shop/dealer for repair, though I like to have an idea what I'm walking into. No ac gauges or vac pump access, so diagnostics are at a minimum.

Car has front and rear ac units. I put the cheap can-filler with gauge on the low port, there was no measurable charge. I pumped a can of refrig into the system, and the compressor began cycling normally. I topped it off in hopes that it would at least get me through the 1300mi roadtrip I needed to make along the west coast, but it proved insufficient. On max settings, all registers (front/rear, upper/lower) blow just slightly cooler than ambient air. Compressor runs normally with the charge, rarely cycling to off. Air flow is normal. Switching to heat shows the blend doors are capable of adjusting. With the radio removed, I can hear the blend door moving from hot to cold and back.

As far as I can tell, everything is functional, but its not blowing cold. because there was no refrig in the system, there clearly seems to be a leak somewhere, though topping with diy can usually produces a temporary fix for a little while. Since both the front and rear are not working properly, I'm inclined to believe the failure is in a front/rear shared component (condenser/compressor). Is there a common failure point in these two-unit vehicles? Can the compressor cycle normally without producing cold air?

 

Systems using R-134a are quite sensitive to having a correct change. There's not a very large window between under charged and over charged. With the single gauge cans there's really no way to know if you have a good charge or not. Plus, with a manifold gauge set monitoring both the high and low pressures at the same time can tell the tech what's happening (charge condition, compressor health, system restriction, etc.).

If the system has a large enough leak and depending on how long it's been low there could be moisture in the system which will impact how effective the system is as well.

Your best bet at this point would be to have the system professionally leak checked, repaired, evacuated, and re-charged.

-Rod