Please allow me to butt in and add a few comments of value. I used to have to do this at the dealership, and the cool down test can be rather frustrating. My record is 20 attempts. To add to the frustration, there's a good chance the cool down test won't pass if you follow the service manual procedure exactly.
The mode door calibration test passes very easily, but the cool down test requires the AC system to be operational. If, for example, you don't want to repair a leak in the system, this test will never pass.
The manual tells you to start with the temperature set to "Cold". To pass the test, the computer wants to see an 80 degree drop in temperature within 20 seconds. How is that supposed to happen when it's already cold? Instead, run the system with the heater set to ""Hot" and with the AC system running. The AC turns on any time the system is set to "defrost". As soon as you press the two switches to start the cool down test, move the temperature control to full "Cold". The calibration should complete after 20 seconds.
If the cool down test fails and the lights keep on flashing, be aware the radiators are so efficient, they may prevent the coolant from getting hot enough to start the test, even when the radiator fan doesn't turn on. If that happens, run the cool down test right after driving at highway speed for a good ten minutes or more. That always led to success for the most stubborn systems.
The heater core gets to around 180 to 190 degrees, but it has to warm air that just came through the AC evaporator. Temperature at the duct should be at least 140 degrees. The evaporator is regulated to hold its temperature to 40 degrees, (high enough that condensed humidity won't freeze on it and block air flow through it). Duct temperature on straight AC is supposed to be around 60 degrees but on most vehicles it will be even less than that. There's the 80 degree difference, but that's at the duct openings. The range is larger where the temperature sensor sits, but it can still take multiple attempts to get the cool down test to pass.
Mar 7, 2020 at 7:34 PM
