If your vehicle is blowing hot air for the first time in a long time, try refilling the refrigerant first. You could simply need some fresh refrigerant.
It’s not that expensive to get an AC leak repaired by a pro. It may not be worth your time or money if you need to buy a manifold gauge just for this. [5] X Research source If your vehicle was made before 1994, it probably uses Freon, not modern refrigerant. Since Freon is a toxic substance and you can’t buy the version of Freon your vehicle needs without being a licensed mechanic, you’ll have to take it to a shop. [6] X Research source If you’re thinking about working on your home AC system, don’t. Just call a technician. The results of DIY central air repair can be disastrous. [7] X Research source
The location of your pressure ports is going to be unique depending on your make and model. If you can’t find the ports, look for small tubes with caps labelled “H” and “L. ” Take the caps off and hook your lines up to these ports. The high pressure line and low pressure lines are different sizes. If you don’t have labels on your pressure ports and your manifold lines aren’t latching on, you probably have them backwards. [9] X Research source
Wear gloves to keep the dye off of your hands. Wipe the nozzle off to remove any minor splatters. The dye isn’t dangerous or anything, but any excess dye will make it harder to find any leaks.
You must bleed the yellow line before starting the vehicle. To do this, hold the manifold gauge away from the engine bay and use a flathead screwdriver or key to push the valve stem where the yellow tube meets the body of the gauge. Keep your eyes away from the gauge and release the pressure you’re putting on the bleed valve once liquid starts to come out. If the high and low pressure lines aren’t open, the refrigerant won’t travel through the AC lines. Just turn the knobs on your manifold gauge counterclockwise to open them up. Refrigerant is not universal, so consult your owner’s manual to see what kind of refrigerant you need to refill your vehicle.
If you have to ask yourself, “Is this the UV dye?” the answer is almost certainly, “No. ” The UV dye will be exceptionally bright and obvious. If you’re working outside, wait for it to get a little darker out. If you’re in a garage, turn the lights off. It can be hard to spot the leaks if it’s super bright. A regular blue or violet lightbulb will also cause the dye to light up so long as the bulbs are LED.
The good news is that almost nobody manufactures UV dyes with co-solvents in them anymore. Unless you have 10-year-old bottle of UV dye, there probably aren’t any co-solvents in there. Common co-solvents include Aromatic 200 and NMP (N-methylprrolidone). If the bottle of dye says “co-solvent free,” you’re good to go.
There are multi-colored UV testing kits that come with a bunch of different colors if there’s something specific you’re looking for. [16] X Research source
UV dye injection is considered the most accurate way to identify AC leaks by many mechanics. It’s basically foolproof since it’s impossible to not notice the dye if you do have a leak. [18] X Research source
