How to check the quality of your coolant
Coolant of good quality will be brightly colored. As coolant becomes old, it usually turns into a brownish, rust colored liquid. At this point the coolant is past its useful life and must be changed.
If the coolant appears to be in good condition, it may be tested.
Ethylene glycol coolants can be tested with a hydrometer. The hydrometer uses floats to indicate the specific gravity of the fluid; you can read the level to find out if the coolant is still good.
Propylene glycol coolants may be tested with a paper test strip. The test strips are dipped into the coolant and then the color of the strip is matched to the chart to determine the condition. This method measures the pH of the liquid, an indication of the acidity level. When coolant becomes old it becomes acidic and can cause severe corrosion. Readings below pH 7.0 indicate that the coolant is acidic and should be changed.
Any type of coolant may be checked by using a refractometer. Put a couple drops of coolant on the window of the refractometer and close the cover. Point it towards light, look through the eyepiece and read the scale.
When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.