91 Caravan won't switch to defrost

[Force Fed Mopar]

Was thinking of breaking out my AWD Caravan in the snow today, but it has some heater issues. For one, it doesn't seem to get much heat out of the vents, which I think is the heater core, as one hose is a good bit cooler than the other. Any good ways of flushing it? Any kind of flush or acid or whatever I can pour in it and soak it? Or just some kind of cooling system flush? I've used a few different brands from the parts stores but haven't ever had great results. Granted they were always the 10-12 dollar bottles.

Other issue is it won't switch to the defroster vents in the top of the dash. Seems to switch to the others okay. Cable need adjusting, or something else?

[Force Fed Mopar]

Never mind, I'm an idiot lol. It does switch vents properly.

Still has no good heat though. Any solutions on flushing the heater core?

[bamman]

I've always been a fan of taking my old 5/8" garden hose, clamping in on the lines, and letting it rip. Both normal ways and back flushing it. Everyone says that you risk possibly rupturing the heater core, but if you are on the heels of replacing it anyway because it is heavily clogged then go for it.

Many report CLR works great. I've used vinegar before too. For my 1990 Dodge Omni, nothing worked. I ended up replacing it.

Another simple but hopefully successful solution is the reverse the lines going to the heater core. Hopefully this breaks up whatever is clogging it.

[Force Fed Mopar]

What is CLR?

[bamman]

CLR is a household cleaner.

http://www.amazon.com/Calcium-Lime-a.../dp/B00009EFEX

Many report that filling your heater core with it, letting it sit a while, then flushing it out will clear a lot of scale.

[ajakeski]

CLR is a household cleaner.

http://www.amazon.com/Calcium-Lime-a.../dp/B00009EFEX

Many report that filling your heater core with it, letting it sit a while, then flushing it out will clear a lot of scale.

Be careful with this method. Because the scale it removes may be the only thing keeping your heater core from leaking.