I have a '96 Civic with almost 200K miles on it. Last year I replaced most of the A/C components: condensor, evaporator, a couple of hoses and the switch in the dash. Finally the A/C was working...until this summer.

When I start the car in the morning the A/C works fine. It can be 80 or 90 degrees outside and it works perfectly. THe car is park in the shade of a large tree.

If I park the car outside at work and then leave for lunch when tempertures are at 100 degrees I get nothing but hot air. The A/C is not turning on. It's done for the day. It will only come on if I can keep the car cool, like in an underground garage. It will then continue to work regardless of outside temperature.

Once the whole car sits outside, which is 90% of the time, and it gets hot the switch will not activate the A/C. What component in the A/C system could be affected by ambient temperatures. Everything else in the system is virtually new.

 

There is a temperature switch in the A/C system but the function of the A/C switch is to detect the temperature of the refrigerant. I dunno if its even possible for the refrigerant to get hot due to the ambient temp but i guess its possible. What you are going to want to do is one day when the A/C doesn't work check if the A/C compressor clutch engages (does the compressor turn). If it does not turn then then you need to find out why it isn't turning. Find and check the A/C temp/pressure switch. If the voltage across the switch (jus 2 wires) is 12v then that means that the switch is open and that is the reason your compressor clutch is not engaged. If the voltage is 0v (or near 0) then you need to keep looking. If the compressor clutch does engage, then you are gonna need to get a manifold guage set and check the pressure on the high side and low side while the A/C is not working.

 

Great I'll check that first thing and report back to you. Also, someone mentioned to me that they thought there might be a vacuum operated relay of some sort and that could be the offending part. Does that make any sense to you?

Thank you.

 

Yea, there is a relay that controls the compressor clutch. I dunno about vacuum operated but anyone that is something i totally over looked so thanks for mentioning it. The #1 thing that i need to know to help any furthur is if the compressor clutch is engaging. If the clutch is not engaging check if the clutch is getting any power. If the clutch does not engage and is not getting power, then you have to check the compressor clutch relay and temp/pressure switch. Also, check to see if the fan is running when your A/C blows hot air.