The heater core is on all the time, and a lot of this heat leaks into the fresh air plenum. This is a recognized design defect, confirmed by a special meeting with a Toyota Technician. By using thermocouples and an IR thermometer I had found that at 75F with the A/C off the incoming air will eventually climb to 116F. So the evaporator has to deal with this heat leak plus the outside air temperature. When the outside temperature climbs above 85F the A/C becomes worthless in CA. By installing a bypass valve for the heater core from an older Camery ($75 for a $5 valve) the heat leak is stopped and the A/C is quite acceptable except on the hottest of days in the sun. At night it will frost the windshield if the dew point is right.
Is there a TSB or a recall? What year is your Scion? Is it under warranty? If so, we don’t need to know more, you just need to tell them to fix it and keep telling them that until the lemon law comes into effect (save all the documentation for each visit).
If it is not under warranty then find a good independent mechanic to see what they suggest and keep watching this thread as someone may have a better answer for you.
Thanks! Scion xA 2004 model year. Their is no factory fix for it. I would have let it go but I get migraines if the temp gets too high. Toyota actually offered to buy back the car after I nailed them as a goodwill gesture. Their explanation was very interesting. They had built the car to specification which unfortunately had an inadequate A/C specification. Since everything met specification, nothing was wrong with the car from their viewpoint. Though in the next generation they would likely improve the specification of the A/C After clamping off the hot water to the heater core as a quick test with a machinist vise it was clear how to fix it. They never fixed it for any of their xA models to my knowledge.
It would be nice to have the HVAC housing out on the bench and see just why this heat leaks,not really high tech stuff.What is Scion low end Toyota?
Wow, that’s very interesting! Could you be specific about what model year Camry to get the bypass valve from? Perhaps even if you referred to one of those online parts sites. (You can email me if you don’t want to post an URL).
There are lots of cars in which the heater core is always hot. Most cars, actually. Installing a shut-off valve to the core is a good solution to your problem, and it doesn’t cost much, either. I remember my old Camry having a valve to control coolant flow to the heater.
Congratulations on solving your AC problem. The simple solutions are always best.
I was never able to find out, as they go by model numbers, and I had used up every bit of goodwill and patience with the my Toyota dealer in allowing me back behind the desk and to go through A/C exploded P/Ls. I think around 98 maybe older. Many type of valves. Small size is important. I can sent you photo if you want. I used the formed water hoses, absolutely required as in my 96, 328i BMW, cut down a bit, electrical bi-valve. Why? Because I was going to use that valve and control it electronically & fully integrate into factory A/C . Cost little more than the $5 valve from Toyota for $75, amazing. BTW Honda A/C is by far the best on small cars–no pecking order.
one question about this fix. does the scion coolant system require the flow through the heater core to complete a loop for the coolant system?
I hate the ac in my scion and would love to have it work better. also I’ve thought about mounting a fan on the front of the ac condenser to increase air flow. any thoughts?
What is the acceped “level” of Scion? Are they a low,mid,high range auto? I have never even seen one.
No, a simple shut off valve works just fine. Think about it and look at the plumbing in the car. The heater core flow is a tiny amount compared to the radiator flow through. The car would immediately overheat if all coolent went through the heater core. Technically it does increase the load on the radiator, but not significantly. Go back and read my original post.
You cannot significantly increase the cooling of the A/C beyond my fix of shutting off the hot water to the heater core. This is because the cooling within the car is fundamentally determined by the size of the evaporator which is just too small, not the condenser mounted in front of the radiator. And the overall system makes a lot of compromises to keep it cheap. The first one being a very poorly designed heater, A/C air box.
They are based on the old Echo now Yaris and were aimed directly at the Teenager market as a first car with some “cool.” Separate sales group and stores. Thus one of the few interesting body designs out of Toyota. Lots of very over priced accessories, mostly worthless, but neat looking. They changed the shift points on the transmission and, put in better brakes and stiffer suspension. I used to get 40 mpg on the freeway, couldn’t believe at first. Lot of fun to drive. Replaced my BMW 328 when I retired and the economy collapsed.
The xA was very popular with seniors as the seat is high and no squatting to get into the car. Though will beat you to death after a couple of hours. Now replaced by the xD which is more macho. The xB more popular with the teenagers, now also replaced and much bigger.
Thanks very much for the info. I have a 2006 Scion Xa, and am curious to know if the problem you found is also present in my model year. I am not knowledgeable enough to just be able to look under the car and see for myself. Would you be willing to share a picture of your solution? I have tried – with mixed results – bumping in some R134a, and insulating the low pressure hose with pipe insulation. Now that the weather has broken, it’s not so much of a problem. But on the 100+ days, the A/C was pretty worthless.
Thanks very much.
I’m sure you have the same problem, and your changes can’t began to address the fundamental problem. The simplest solution is to take it to an A/C place and tell then that you want a hot water shut off valve to the heater core, they can also easily show you the under-hood plumbing to the heater. In fact just about any mechanic should be able to do it. I didn’t even bring a cable inside the car. I just flip the valve manually by raising the hood, so during the winter season It works as it should. To really fix the problem the heater box requires a completely new design. The heater/AC box is a rather complex assembly.
Toyota’s reasoning was typically bureaucratic. Yes, it does not cool sufficiently. But it is built according to our engineers specifications. Therefore there is nothing wrong with the car. In future versions we may change the design. I suspect they fixed it in the xD, as it was a major complaint for Toyota.