had 2 mechanics check it out at different times and then I ran across this forum, van heater started not heating after putting in a new radiator about 3 years ago, it had started leaking badly and mechanic said it was very, very dirty inside the radiator (wife drives it and she is getting really upset about having to drive in the cold), engine temp seems ok, maybe a little low, heater core has been flushed, new thermostat (twice), water control valve in the heater hose seems to work, took it out and inspected it and it opened and closed ok he said???, flapper arm looks like it's sliding over enough with cable control from dash, he took it loose from cable and made sure it was slid over all the way, mechanic wondered if maybe water pump not pumping enough water correctly through water heater hose, but that was a pure wild guess, he's totally stumped!? Any ideas! I've looked through the forum and seen a few ideas, but we have tried about everything I can think of. Also, my wife did mention she doesn't think the AC cooled as well as it use to in the summer though and she says it feels like to her now it's blowing in the cold air from outside into the interior??? Is there another control we are missing besides the flapper??? Tried cardboard in front of the radiator, it did bring up the engine heat more, but still little difference on the interior heat, she says the more she turned the fan blower up the colder the air got coming inside! Also, blower only works on high and low, any ideas there as well?

 

Feel the two hoses that go to the heater core. If they're both about the same temperature then your problem is a bad heater core.

 

Replace the blower resistor. You have to get it from the dealer and it's about $20.

 

where is the resistor located so I can find it to replace it. Also, don't quite understand about the heater core being bad, you can hook a water hose to one side of it and water comes out the other side, please tell me more, THANKS!

 

Under the hood, passenger side, big black box, about 16 inches straight above the blower motor look for a flat 4-wire connector going to it. It's about $20 for the part from the dealer (only place to get it) and it's held in place by 2 screws. I'd say about a 3 minute job to change it. Inspect the connector while you're at it because some of them like to melt. If that happens you'll have to get the repair pigtail from the dealer (about $55), part #5019941AA.

I know this because I just had to replace both the resistor and pigtail. There is an outside chance that the problem is a bad fan speed selector switch on the dash, but usually the resistor is the first to go.

Regarding the heater core, flow doesn't necessarily mean heat dissipation. If the inside of the core is coated with rust, dirt, radiator sealer, etc. the ability of the core to absorb the heat from the coolant and dissipate it into the air blown through it is significantly reduced. The telltale sign of this is if both hoses are fairly close in temperature because it means that the heat isn't getting pulled out of the coolant as it passes through the core.

Your own mechanic said three years ago that it was, "very, very dirty inside the radiator", did he not? Now add three more years of deposits onto what was already on the core back then and you end up with almost no heat today.

 

When you had mentioned that the heater core was replaced, it was full of nasty stuff. Did you have the cooling system totally flushed then? If so, did you have 50% anti-freeze (NOT long life stuff) and 50% DISTILLED water added??? If regular tap water was added to the vehicles cooling system, those nasties will come back even faster since the corrosion level gets higher. Distilled water is only 64 cents a gallon at Wal*Mart.

And like alloro mentioned when the engine is warmed up; the heater hoses to and from the engine, is one hot while going to the heater core while the HVAC system is set to heater mode and the other hose a little cooler? Likewise, how about the hoses to/from the radiator?

There is a side door air vent to the HVAC system that connects to the inner fender wall on the passenger side. If that door is fully opened or stuck the open postition, then the outside fridged temps will mix with the heater core providing mild heat at best. This outside air door is controled by a vacuum actuator. How are the vacuum lines to the HVAC?

You have a Gen-1 HVAC system.

 

Based on everything you have done so far, and everything you have corrected and/or replaced so far it does sound like a vacuum problem now. Have to agree with stev. Air director probably stuck in the wrong position.

 

Thanks to all! Some more questions if you would please bear with me please, I am in a small town, not very many mechanics, I may just have to try and do this myself. I will check the heat on both sides of the hoses, IF the temp is the same on both sides of the heater core can I flush the system to correct that and if so what do you recommend as the best way to do that, or do I need to just bite the bullet and replace the heater core and if so how do I replace it, it looks like a major job! Also, where is the air deflector on the passenger side at more exactly and how do I get to it, if I can find it and it is stuck open I may just figure out a way to permanently close it. You know what is strange, I have a 1990 Chevy 4x4 pickup (auto w/AC) I had a new radiator put in it this summer and the heat doesn't work very well at all on it now either!? The local parts house didn't have the exact original, the old one didn't have a built in oil cooler, the new one he put in had a built in oil cooler, but didn't hook it up as the truck did't have the hookups, but I doubt that would make any difference, he did put in a thermostat, and I just put another one in myself to make sure, still same results, engine temp seems OK??? I know this is a Dodge Forum, not a Chevy, but I thought someone still might help with that as well...

 

I decided to really check in to it myself (I'm just a wanna be shade tree mechanic sort of). Basically water runs good to the heater core, took hose off other side it just barely trickles out of heater core, (it was hot going in and cool coming out, but I decided to check it out further) sounds like mecahnic didn't do a real good job of flushing it as he told me OR it plugged back up again??? he did tell me he hooked a water hose to the heater core and blew out some gunk and it ran freely, but he hooked it all back up and it still didn't heat good, so it may have had more gunk in the system and pluuged it back up, I now think he did not do a total system flush. Is the Prestone radiator cleaner/flush a decent choice to try or do you guys recommend something else to start out. I can tell replacing the heater core is a major under taking in this Van. Also, finally found the blower resistor, it is in the firewall behind the glove box insert...

 

It seems that you have no choice but to use the Prestone cleaner/flush method for now. The corrosion inside may have already built up and caused too much damage. With the engine running, where does the temp guage sit at? It should sit around 180-220 when the van is warmed up. Once you totally flush the system clean, drain it the best you can. Next run a cheap two gallons of "distilled vinegar" with distilled water through the loop as well. This will help purge the tap water residue from the cooling system. Drain that as well. No you are ready to put the normal amount of coolant and distilled water back in the loop. BUT, make sure the first flush gets everything out. (PS, do not use regular vinegar since it's made from apples. It has tooo much sugar that will lead to other problems.)

As for the Chevy, I don't have much of a clue. To increase the vehicle temp, you will need to use a 195 t-stat for the Chevy.