The Toyota T100 is a first-year model of the Toyota full-sized pickup truck line, which was offered with optional air conditioning. The A/C system can leak or become damaged, and troubleshooting the system is complex because it is spread out over the engine bay. The average T100 owner can diagnose the air conditioning system in about an hour.
Many components of the air conditioning system will make sounds when they are about to fail. The sounds become loud when they have failed. The compressor can make a chirping sound, indicating it requires more lubricant. Its attached clutch can make a grinding sound, which means it could fail soon. Failed compressors and clutches will make a horrible racket, and could seize completely. Evaporators and condensers usually simply leak, which makes a slight hissing sound.
UV dye is used to locate a definite leak in the freon coolant system of the air conditioner. On the T100, the dye is injected with a store-bought valve and can, plugged into the low side nozzle of the A/C system near the evaporator. The T100 was built after the switch to 134a freon, which means the nozzles only fit the correct valve. With the car running, the valve is opened, letting the system vacuum in the dye. Later, after using the A/C for a period, a black light will show the leaks and their source. The UV dye will glow green under a black light, and a drip or spray of bright green anywhere on the A/C system is a sign of a leak.
Sometimes, the system can stop functioning due to a lack of electrical power, or the operator controls have malfunctioned. The primary wire on the T100 for powering the clutch, which engages the compressor and the system, is a green wire coming from the top of the compressor. There are two fuses, on at the driver's kick panel fuse box, and another under the hood at the primary fuse block. If these have blown filaments, replacing them will fix the immediate problem; the real reason for a blown fuse may not be apparent.
Using a wiring diagram for the T100, locate the route of the power going to the system, and have the computer checked for malfunction (most auto parts stores will do this for free). The compressor also needs a good grounding wire, so check all grounds in the vicinity of the compressor. Inside, the controls are vacuum-actuated and may be leaking. Listen for proper operation when sliding the controls. If a hissing does not stop with a change in operation, the vacuum system could be to blame.
