AC issue

I found early in the am and evening the Prius knows the air outside is cooler than inside and uses it to cool.
It doesn’t mean your compressor is working or that there is Freon (or its equivalent) in the system.
For example if the air is 73 Outside and the temp is set to auto A/C 73
The fan will be on low both in the cabin and in the engine compartment. Lower the temp to 70 and the cabin fan increase speed and continues to do so with each decrease in temp to high.
When it is on max you can go to the engine compartment and if there is Freon and also a working compressor you will find the Hi and Lo pressure Lines to be hot and cold respectively.
If the compressor is running without coolant or with little you will notice that the fan and the engine come on more frequently to satisfy the power for the compressor (it’s electric not belt driven), than when the A/C is off.
Easy right?
If you find the compressor is on and there is no difference in the temp. at the H and L lines then you have no 134 a refrigerant. Or you have too much.
Fix it.
Remember you ad coolant to the Low pressure side with AC on max. And you need a gauge to get it to the correct pressure given the temperature that day.



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Your brothers Prius problem sounds like he has a refrigerant leak. Which you can measure with the new gauge you get with your refrigerant.


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The fan system uses an ac pressure switch so if the refrigerant is low the fan does not come on in high mode. Fans should go max speed the second you turn on the ac to cool the condenser. If no high fan speed you are low on refrigerant and you most likely have a leak and need a die test done.

This switch is on the passengers side of the front condenser.

 

The wiring diagram shows the control of the fans to be a fairly elaborate scheme.

Powering "FAN NO. 3 Relay" is what puts both fans on at low speed, and adding "FAN NO. 1 Relay" and "FAN NO. 2 Relay" is what kicks them up to high speed. (NO. 1 and NO. 2 always operate together, their coils are wired to a common junction).

Powering NO. 3 to put the fans on low can be done by either of:

• The hardwired engine water temperature switch, or
• A direct signal from the A/C amplifier's "CF" output pin

Powering the NO. 1 and NO. 2 relays to kick the fans up to high can be done by any of:

• The hardwired A/C pressure switch, or
• Direct signal from the A/C amplifier's "RF" output pin, or
• Direct signal from the engine control module's "FAN" output pin

So it's tricky to say exactly why the fans are running, on low or on high; there are a couple of simple switches involved, but also a couple computers that get to cast votes based on what they think is going on.

If I understand correctly, the setting of the hardwired A/C pressure switch is for "higher than you want", so it's there as a fail-safe, but under normal circumstances if the fans go to high it will be because one of the computers said to.

 

Hello all. I have a 2006 Prius and the AC isn't working. The mechanic (Firestone, not a Toyota dealer) "recharged" it with freon and claimed the pressure was good, the compressor is working, and they don't suspect a leak, but they got the B1421 code and concluded that the solar sensor needs replacing. They said it was reading the inside car temp as -200 degrees and thus, the AC wasn't getting kicked on. I'm therefore not sure how they know the compressor is working, if the AC isn't getting kicked on, but they assured me that they forced it to come on (somehow).

They quoted me 2.5 hours of labor to replace the sensor, because it entails removing the dash. Does any of this sound fishy? What am I or the mechanics missing? I don't really want them to remove the dash and replace the sensor and have the AC still not work...I'd be out $500 and still have no AC. And I'm nervous that the dash won't get put back together properly. I guess I don't trust that they know what they are doing, though I'm trying to trust them. Please help. Thanks.

 

Brake clean is not recommended but even if I was in a pinch I would use it too and I have.

 

That's entertaining.

B1421 is essentially a code that is useful for figuring out whether the solar sensor works or not. If the sensor is working right, you will not have B1421 if you pull the codes while in bright sunlight, and you will have B1421 if you pull the codes while indoors or in the shade or at night.

I've never heard of one failing. It is pretty tedious to get to for replacement.

The solar sensor is not responsible for reading the inside car temp. That's a separate thermistor, usually kind of in the lower dash panels above the driver's right knee. (In Gen 1 there was a little louvered spot in the plastic showing where it was.) Not nearly as much work to get to.

There is a narrow ribbed plastic hose leading to it, and an electrical plug to connect. (The hose leads back to the HVAC blower, so when it is running, a stream of moving air gets sucked over the thermistor to make sure it is really reading the cabin temperature and not just some stagnant air above your knee.)

Leaving that electrical plug unplugged is a common mistake any time somebody has been working in that area of the dash. Then you get the telltale effect of the inside temp reading some crazy number and the heat or A/C not doing anything at all except at the most extreme temperature setting.

 

Thank you for responding so quickly. I have an appointment to bring the car in tomorrow, and my gut tells me it's a mistake to replace the solar sensor without further investigation. Thus, my post here. It sounds like whether the solar sensor is working or not has nothing to do with the AC not working. Is that correct? In your opinion, ChapmanF, should I ask the mechanics to look into the thermistor instead to rule out why its reading the -200 degrees? (I'm not even sure what reading they are reading.)

The car is also making a strange buzzing noise. I think I read in an earlier post that that could mean the compressor is not working.

 

Yes, that's exactly what I meant.

If there was any recent work done near the driver's side lower dash, there's probably nothing really wrong with that thermistor either, other than having been unplugged and not plugged back in. Familiar story around here.

 

I'm not aware of any work done in the lower dash. They recharged the AC, but otherwise, I don't know why or how it would have gotten disconnected. ??? I'll look at it myself and see if I can see any disconnected wires. Thanks.

 

I can't see any disconnected wires. I guess my next question is should I go to a dealer to diagnose this problem?

 

I'd forgo going to a tire place and go to a specialist auto a/c shop. When your Firestone guy "recharged" it, did he evacuate the system first before adding a precise charge of R134a refrigerant?

 

Good question. I have no idea. I will ask.
Also, I’m not sure how to go back to them to tell them the solar sensor isn’t the fix, because what do I know? What does the solar sensor do anyway?
Also, the car does make a new buzzing noise. Could that be a different part, like the condenser or compressor?

 

Yes, it could be the compressor. That is why I asked about whether the charge was done correctly. Topping off is the number one reason compressors fail.

 

It makes the fan speed up a little when you drive out of shade into bright sun, and slow down a little when you drive into shade.

 

I asked...they said they did evacuate system and put in “R34A”....presumably he meant R134A.
He also said the compressor kicked on at first, thus they concluded that it works. I mentioned the thermistor and he wasn’t familiar and said he’d talk to the master tech.

 

If you read the cabin temperature as -200 over the diagnostic connection, there is a problem with the cabin temperature sensor whether or not you noticed anything in a quick check for loose wires. And that's enough to give you your issue, because how much heat or A/C you need is based on that reading.

 

I changed my compressor with used one and a new condenser. Had the rest of the system flushed. I vacuumed for about 30 mins. Blows cold but only getting 60 degrees out of the vents with out side temp around 80 degrees.

Edit: okay...took a drive and the temp gauge dropped to about 44 degrees. It's blowing nice and cold

 

Firestone never did call me back. Weeks later, my AC still does not work. Dealer will charge $150 just to diagnose the problem. I don’t know of any auto AC specialists. I’m stuck.

I normally drive with the AC on all the time, even in winter. (Not sure if that’s good or bad.) I’ve noticed better gas mileage lately with the AC turned off. Is that normal?

The other day, I needed the front defroster, and I noticed the same new weird buzzing noise that happens when the AC is on, but this time, it was the defrost that was on, not the AC. The defrost didn’t seem to work either. What could be running amok here that would cause both the AC and the defrost to not work and make a weird buzzing sound?

 

A/C is automatically turned on behind the scenes when you select defrost, to dry the air so it defrosts better.