A/C stops working above 90°

Hi,

You need to check the evaporator and see if it is freezing. I suspect you have an expansion valve issue. Basically, this controls the amount of expansion/evaporation the refrigerant does in the evaporator and when this fails, it allows the core to freeze and then it blows warm air because the ice does not allow the air to be cooled as it can't flow through the evaporator.

The evaporator is located in the HVAC housing behind the dash. More than likely you will be able to see it by following the AC lines in from the engine compartment and then looking through the fresh air inlet. Also, if the AC lines going into the firewall look like they have ice on them then you can be safe to assume the evaporator is frozen.

Last thing you can do is get the high and low side pressures while it is blowing warm. So drive it around until it starts doing this and then hook the gauges up to it. If you hook them up after it has sat, they will probably be normal because it takes about fifteen minutes for the evaporator to freeze and if this is it, we want to see what the pressures are when it is acting up.

Let me know what you find. Thanks

Okay. That is great. The unfortunate thing is when you have equal pressure around 100, this indicates the compressor is not operating.

Before you go back to where you got the compressor from, I would just hook your gauges up and let the vehicle sit there and run while you monitor the pressures. I would guess that the pressures are closer to normal when it is blowing cold but if the compressor is not functioning at all then they will be about 100 on both sides all the time.

Let me know what you find and we can go from there. Thanks

Yeah. Sounds like the compressor is not operating. Here is a chart that shows the proper pressures based on ambient temps. When they are equal it just means the the compressor is not pressurizing the system so the high and low side become equal. In other words, it is a static system.

You will want to make sure you have voltage going to the compressor before you replace it again. There is a fuse and relay that control the compressor so if you measure power and ground at the compressor when it is on then they are both okay. If you do not, then check both and test.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit