A/C(Htr) fuse Intermittently blows

How often does this happen? Within a few minutes, once a week,...? What conditions? Is it just with A/C use? How does the system work when it is operative?

Intermittent faults are the worst to get at.

The A/C compressor could blow that fuse, so I would be looking into that. The diode you mention is to protect the relay from pump motor generated switching transients, and it would be an unlikely candidate, IMHO.

Also, is there any possibility of rodent damage? Frayed wires someplace that are touching?

 

It sounds like you are doing the best for now. I don't know where that diode is located. They are often tucked away somewhere. I would say that it would be highly unlikely for a diode to fail intermittently, sufficient to blow a 10A fuse, and not become a hard fault in the process. So I would continue to focus elsewhere.

When you say you eliminated the water pump as a culprit, does that mean the fuse has blown with the water pump disconnected?

 

Yes, that pump runs only when the engine is *not* running, to keep the hot coolant moving through the heater core. I guess you have put as much logic to the problem as can be, so there is not much more to say until some more cause and effect observations can be made.

 

Pulling the water pump relay for a few days will eliminate the diode and pump motor. I f it still blows the fault must be else ware. I agree with Nh70 diodes do not normally go intermittent short circuit but there can always be a first time.

It is also possible the relay itself could be at fault with an intermittent shorted coil.

John (Britprius)

 

Even the relay block becomes Byzantine on the Prius. The A/C WP relay, and the diode as well, is listed on the engine room relay block *inner circuit*, which I suspect means that "some user disassembly required". I haven't been in there, but it is where the fusible links are located, and involves taking things apart to get to the next layer.

 

The diode appears to be mounted on the underside of the relay connector in the engine compartment fuse/relay box.

John (Britprius)

 

By lifting the wire from the engine ECU that activates the pump relay, that indicates that the problem is with the relay or the wiring going to the relay. No one has come up with where the relay is located in the engine fuse box? I have a 2010 so cannot help with your car.

From what I understand the heat coolant storage is to help with the ICE warmup in cold weather. Without the pump you will be extending your warmup time and cost a little mpg.

 

The heat storage mainly helps the MPG when making frequent stops, especially in the winter. If it is a commute car, one round trip with a long space in the middle, then it won't help all that much. Since it is not used in EU models, it is possibly a small negative effect in some situations, because extra energy is expended to heat the storage system that may not get reused.

 

Hey I've had the similar problem with my 2007 prius over the years, but it won't blow any air when turned on, especially in summer (LA). AC won't turn on at all then may kick in after a few minutes or not all. I've got no error codes and read somewhere that possibly switching out the 12v battery could fix the issue. When it doesn't turn on I can hear a louder buzzing type type sound.

Does anyone know how to fix it? Such a strange blizzard issue. I heard clearing the error codes can fix it but I don't have any in diagnostic mode.

Thanks and really appreciate any advice.