AC blows cold air when car stopped, hot when moving

Good place to check but is cold air coming out from somewhere else if the blend door is bad that's just going to put your air out some other vents or something along those lines if the air conditioner will turn on and it's running and it's on truly LO not 77° no heat is being introduced into the system to blend with the cold then somewhere cold should be coming out of some hole One would think anyway I'm starting to have trouble with the door that moves that same air I don't know if that's the blend door or is it called something else I would think the blend door would be the door that would move and allow heat to be added to the cold to come up with a temperature that you want coming out the vents like 77° so on and so forth so what exactly happens when the car is driving the air just disappears?

 

Yes, the blend door is what controls the blend between air that goes through the heater core, and air that goes around the heater core.

Air that goes around the heater core doesn't get hotter.

Air that goes through the heater core does get hotter (except when the heater core isn't hot).

The heater core is always hot when the engine is warmed up and the water pump is turning.

So the position of the blend door controls how much hotter the air gets.

If the door is all the way "around the heater core", the air doesn't get hotter at all.

If the door is all the way "through the heater core", the air gets lots hotter.

In cold weather, when you really want heat, the water pump keeps running even when the engine is stopped, so hot coolant keeps flowing through the heater core and the air stays hot.

In hot weather, when you're trying to cool, there's no reason for the water pump to stay on when the engine is stopped, so the water pump stops then too, and then the heater core doesn't add heat.

So if your blend door is stuck directing air through the heater core when you are trying to cool, you end up getting cool air when the engine is stopped, and hot air when the engine is running.

 

I suspect it's more of a problem with your refrigerant level not being correct than anything else.

 

So the heater core in the Prius is nothing like the heater core in a regular car or the valve that controls it so in other words there's no valve when I turn my Prius down to low lol that's still allowing the heater core to have heat on it in it meaning that heat is radiating from that thing on the firewall but in the cabin seriously well that's pretty fubar. So then the only way to get the heater for to not fill with heat in the summer is to pull the hoses on the firewall and put them together not allowing coolant to flow through the heater core at all in the summer well I wonder what kind of difference it'll make in the car internal heat I've never been hot before in the Prius personally I know some people are and with the heater core staying hot all the time because it has no valve to turn it off for whatever reason that's something I guess there must be some other cars like this too I know my Corollas I turn the heat off heater core is as cool as the inside of the car is.

 

The last car I worked on that used a valve on the water side of the heater core was an ex's 1965 Galaxie 500. (I remember a newer car that worked that way too, a Mitsubishi from the early '70s.)

The always-hot heater core with a blend door that sends the air either through or around it, and no water valve, is pretty common in "a regular car" in recent decades. You feel the temperature change immediately when the blend door moves. People like that.

And in a Prius, "my A/C blows cold when the engine's off but blows hot when the engine's on" is pretty much pathognomonic of a blend door that's stuck in the heating position.

What year Corollas? I looked up a random 2016 Corolla heater core piping diagram ... no water valve.

 

Yeah I generally drive really old cars like 82 Corollas 74 Corollas stuff like that but at least down here in this house I know in a pinch I can just put the heater hoses together outside under the hood and then have no heat anywhere in the cabin isolated insulated or not It just won't be there I mean even in the winter I don't run much heat I'll put it on you know when it's icing and what have you but that's about it I'm in my outdoor clothes. So I just reconnected in about late December and then in May put the connector in and put the hoses together because the summer's long and hot and hotter as the years move forward it seems.

 

Behind the glove box is reasonable access take the shock absorber damper thingy off the lower glove box the right side it's a slips off let it hang squeeze the glove box at its edges and it just falls out and hits your knees lift it up set it behind the driver seat You should be able to leave the upper glove box intact If not be careful taking out the screws and withdrawing it because it's very sun damaged and the hinges and the spring mounts for the door opening up automatically will easily break. Other than that I really not fooled with the motors that operate the damper doors and all that should be pretty straightforward whether you can get away with cleaning
Them internally or what has to happen parts car replacement buying new not sure about that.

 

You could always put the damper door where you want it for the given season and unplug it so it doesn't move no matter what the person in the car does. Probably inconvenient but it'll keep it at one place or the other until you bite the bullet and tear the mess down and replace whatever goes on in there whether it's the potentiometer or whatever the electronic pieces in there that aren't work I don't think it's gears that break but hey maybe so.

 

In some cases some part of the door has busted or come unconnected or jammed inside the heater enclosure. There was a thread here where somebody did some kind of amateur-laparoscopic surgery with skinny screwdrivers or chopsticks or something and got it reconnected without all the expected disassembly.

I'm not sure I can think of an easy way to search up that thread.

 

It's probably the dry heat and intensity of said heat with windows rolled up and so on that's probably helped mess the servo up actually maybe not If you maybe spray some WD-40 on the little shaft or whatever that passes through but creates the lever sometimes you can get it to move if something is broken there and really gotten jammed against something else then not so much.

 

The repair manual will flat out say to take the dash out first. After that, access is easy.

Figuring out how (starting with whether) you can do the repair in less work than that is a personal exercise.