Hi all! Recently I bought myself a cheap, high mileage Prius II 2005 and I absolutely fell in love with it. I do all the maintenance myself and since the car came with no history I already among others did; oil and filter, replaced coolant, gearbox oil change, spark plugs, air filters, ‘new’ drivers seat, all brakes. The Prius drives great now and sometimes even manages to get 3.9l/100km (60MPG)!! Anyway, there is one thing left that is keeping me up at night, the AC. I went to a local shop to get the refrigerant vacuumed out and replaced (with the correct refrigerant and oil!), since the AC was not working great. After that, the AC still doesn’t work as it should. When the car is stationary, the AC just blows warm/outside temp air. I can hear the compressor kicking in and it sounds to my untrained ear, healthy. When I start driving and coming up to speed (minimum ~50 kmph/31mph) I can start to feel cold air, which will become colder when I drive faster. I connected my laptop with Toyota Techstream to the car. When I do tests on the compressor speeds, the compressor gets to the selected speed (RPM) no problem. When I check the data, I can see the evaporator temp come down from 30 degrees celsius (86F) to around 10 degrees (50F) when I’m driving. Coming to a stop it climbs fast to 30 degrees again. There are no error codes. Since the AC cools when there is enough air going through the condensor, I suspect that the ECU is not sending the signal to the fans to spin at high speed, but I’m a bit at a loss as to where to go from here. The fans spin, but not fast. The direction is correct, tested it with a sheet of paper and it gets sucked towards the car/engine. Any help would be greatly appreciated, especially since we're going on holiday next week to Italy. PS, today when getting in the car and stationary, the AC blew cold air for the first few minutes (5 degrees C (41F) evaporator temp) before getting hot again...
Small update. Checked both fan relais with my multimeter and they check out fine. Drove on the freeway today for around 20 minutes and the AC was supercool. After getting of the freeway, the temperature climbed a bit, but still ok. When getting to a stop the temperatures unfortunately climbed again. So to me this really sounds like an airflow/fan issue. Anybody has some suggestions?
What does the condenser look like - what is the condition of the fins? If the fins are corroded and crumbling (or clogged with dirt or debris), that will reduce the ability to dump heat. Try spraying water on the condenser when it is blowing warm air, see if that helps. The radiator fans turn on LOW with A/C function. The fans turn on HIGH only when the ECM senses high engine temperature. Posted via the PriusChat mobile app.
Thanks for the reply! The condensor looks like I think you would expect after 20 years, but could be worse I think. IMG_0491 by Michaelz posted Jun 22, 2025 at 2:51 PM IMG_0494 by Michaelz posted Jun 22, 2025 at 2:51 PM I already did the test with water, but didn’t seem te effect temperature much. Maybe I was not spraying enough water. I could test again. When the AC works for a while (at idle) after it has been sitting a few hours, the fan does sometimes turn on high for a few seconds. I don’t think it does that anymore when the AC doesn’t cool. Maybe the airflow is bad through this old condensor and can’t overcome the heat coming from the radiator anymore. I could try cleaning it a bit more and maybe straighten some cooling fins.
Straighten the fins and then clean it from the front once or twice with a can of AC cleaner (the ones used on the outside condensers on home AC units) and then rinse with water. That is, a light spray of water to wash away the remaining soap and dirt, preferably distilled - don't aim a hose at the fins through a nozzle. One of those canister sprayers which is filled and then pumped up and has a nozzle with a fine spray will work. Pressure sprayers are a complete and total no no. I could feel the difference on our AC after cleaning it. It was working pretty well beforehand, but better after it was cleaned. What worked best for me for straightening the fins were plain old wooden toothpicks, the type that are cylindrical with a point at each end. Put the tip in at the wide end of each triangle and slide it up (or down) to restore the triangle shape. Doing that with on two adjacent triangles, one from the top and one from the bottom, is also good. It more often bends both triangles into close to the original shape, whereas doing one at a time it is easy to spread it out too far. This is exceedingly tedious, hours of work, and the bumper should really be off to get the best access. If the OP has skinny hands it can be done through the openings in the plastic in the front. There were a lot of tiny little rocks stuck in the triangles. Those can be vacuumed out if they cannot be picked out with the toothpick, but use a lot of caution because bumping a vacuum nozzle into the fins will bend them. Also, keep your fingers well back from the business end of the tooth pick. There will be torn fins sticking up and those little suckers are as sharp as razor blades. I also used a very small metal pick with a 90 degree bend near the tip to start lifting up fins in sections which were severely mashed. Sometimes the fins are so close together you cannot get a toothpick in. The fans should be coming on pretty much any time the car stops and the AC is on, at least on a hot day. If they aren't doing that after the cleaning then there is some problem there.
