Ok, I need some help here. My A/C quit working and after some testing I found that if I use a test light on Relay/fuse 34 in underhood fuse box, it works! I use test light on ground and touch connector 86 of rrelay and A/C comes on. Otherwise no A/C. Any help out here?

 

please clarify what comes on. the fan inside or the compressor clutch engages. if the clutch is not engaging the pressure is too low to close the pressure switch to allow the clutch to engage. if the clutch is not engaging, remove the connector at the pressure switch and short between the two wires. if the clutch then engages you will know the switch is bad or the freon is low. likely just the freon is low. my 98 is low right now and needs servicing.

 

Clutch does not engage. The preasure switch has 3 wires, what do I short? 2001 Z06. When I ground post 86 on relay 34 the clutch engages and air is very cold. Just can not turn off untill I unground post 86. what else stops A/C from engageing clutch? Outside air temp sensor? How do I bypass it?

 

Anybody got any more info?

 

You last comment indicates you have the Dual Zone A/C which does use the external air temp sensor to determine whether the A/C should be allowed to come on. What external temp is your display showing?

If the EAT reports a temp below ~36F to the unit, the A/C will not come on. It is very common for the EAT to fail due to corrosion around the connector. It's located below the passenger headlamp and extrudes into the radiator cavity just forward of the air dam on the passenger side of the cavity. The best way to get to it is get under the nose and remove the bottom panel, but you can reach it from the top witht he headlights raised and the hood up.

If you disconnect the sensor, the system should default to an external temp of ~57F which would allow the A/C to come on. Be aware that often the connector itself is corroded and shorted which can still report an erroneously low temp even with the sensor disconnected. Try disconnecting the sensor and if you're still seeing a low temp on the display you may need to cut the connector off. But remember - the display temp does not always change immediately if the car has been recently started so I believe you need to drive the car above 45MPH to force the unit to update the temp.

If the sensor is in fact the problem, it's a cheap part (less than $15) and you should also get a new connector. Spray the connector with silicone or electrical grease to keep water out in the future.