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Heater problem

10K views 21 replies 11 participants last post by  streetbob 
#1 ·
I just bought a used 02 Ram and the heater isn't working like it should. When I first turn the fan on it will blow hot air for about 5 seconds then it cools off. If I turn the fan off for a few minutes and turn it back on, the same thing happens. The a/c works fine, just not the heater. Any ideas what might be the cause?
 
#4 ·
Its still possible that the themostat is bad(in this case possibly stuck open), even though the truck reaches N.O.T. causing your case of just blowing the cold air...Check the hoses that run from the thermostat, and the heater core to see if they are hot or cold...They should be hot(or fairly warm anyway)...Now if your coolant is at the proper level in the RAD and reservoir(without any leaks from hoses, and the RAD), the thermostat is working properly and its still blowing cold air, check to see if you have a leak inside your truck or a strong smell of coolant coming through the vents, then thats a good indication of a bad heater core...
 
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#8 ·
Do you hear the air diverter valve switching positions when you change from heat to defrost to bi-level?

If not, the little valve in your HVAC distribution box is sticking, the valve may be defective or there's a connection/electrical problem there.

That HVAC distribution box is under the dash.
 
#9 ·
I think it may be the blend door. I know my mode 1 door is broken, air only blows from the vents no matter what the setting is. I suspect the blend door is broken too. I don't hear it change when i change from cool air to warm air, but i can get warm air briefly though so I'm not sure whats happening.
 
#10 ·
Could be a blend air door issue or even a partially clogged heater core . Might try clamping off the heater hoses , removing them from the heater core , then take a garden hose with good pressure and flush the core with water back and forth between both nipples . Reinstall the hoses and see what that does for ya .
 
#11 ·
Ok, so here's an update on this issue. I ordered a Heater Treater Blend Door and when I disassembled the dash it turns out the blend door is fine and working properly. My next thought, as some of you suggested, is a clogged heater core. However, both heater hoses get hot, so I'd think the heater core would be ok, correct?

Thermostat has also been metioned, but it reaches operating temp just fine.

What should I do, go ahead and flush the core and replace the t-stat? Look somewhere else?
 
#13 ·
Another update, flushed the heater core, but it didn't change anything. Still blows hot for about 5 seconds then cools off.

Also, should my passenger floor board be wet after the flush? It appeared to be only water, not coolant. I thought maybe water got through the opening in the firewall where the heater core ends come out. Or could it be worse, like a leaking core? I haven't noticed any coolant smell or wet carpet before the flush.
 
#14 ·
No, you shouldn't have any moisture in the interior. Its possible you may have sprung a leak if you flushed the core with high pressure water. Remember, the cooling system is designed for 16 psi when its new. A weak core would be more susceptible to leaking after a flush.
 
#20 ·
The HVAC system on the RAM is a dual chamber system that is configured as either single or dual control(separate temperature control knob for passenger side). On the single control a difference in temperature between the passenger and driver's side can be due to a temperature gradient across the heater core. The flow through the heater core is a single input that spreads into multiple flow channels then comes back together at the exit hose. Half the channels span the driver half of the plenum box and half for the passenger.

The core tends to build up blockage on the passenger half of the core over time and you'll find diminished heat on the passenger side over time. The diesel engines seem to be particularly susceptible to this problem. The solution is an aggressive radiator flush to clear the core. Prestone makes a good flush kit with cleaning chemicals that is available at Walmart. You can disconnect the heater hoses and flush backwards and forwards to clean it out. You also need to flush the entire radiator system to keep more gunk from just clogging up half the core again. Routine radiator flushing is supposed to be ongoing maintenance and is especially important on the RAM. If it's been more than two years...FLUSH! I got all this information from the guys at HeaterTreater. They are awesome and I installed their Mode 1 door and re-circ door fixes on my truck with great success at signficant savings over what the dealer wanted.
 
#21 ·
To revive this thread, I'm in a very similar situation. No heat in my Ram, and haven't had heat really for about 2 years now. Just never had the $ to fix it, and last year it sat on my driveway while I was away at college. Now I have it with me at college and can't deal with the cold any more. We had it looked at when it first went out, but I don't remember what they said it was, and they weren't certain about anything, it was their best judgement. My truck is doing the same thing as the OP, when it's turned to full heat, and I turn the fan on, it blows hot air for about 5-10 seconds and then gradually gets cooler until it reaches ambient/cool temp. The thing is, I can do this multiple times while driving. For example, I can do it once, and then maybe 10 minutes later I can do it again. And repeat...

Regarding thermostat, radiator flush: This past spring the truck overheated on me and we had the radiator flushed and the thermostat replaced, and still no heat. Would the radiator flush have also cleared out the heater core?

When the air blows, I don't smell any antifreeze through the vents, so I guess that means no leaking core, right? Also, today I listened for the actuator (I think?), and as I turned the temp control from I heard something behind the cupholders, I guess it was the blend doors moving? So a mode door isn't the problem? Although I do notice the air comes out noticeably stronger some vents than others, especially on the driver side vents vs passenger side. But that's a different mode door right?

I'm thinking it's a heater core problem. If it were a blend door problem, I wouldn't be getting that first 5-10 seconds of hot air, right? So does this sound indicative of a clogged heater core or a broken one? Is there any other way to check?

Thanks!
 
#22 ·
Mine had the exact same problem. The heater core is plugged. I used a garden hose with a pressure nozzle and flushed the heater hoses both directions, got some junk out but didn't make a difference. I took it to a local radiator shop and they used something with water and air and flushed the system and it works again.... not 100% but I get about 103 degree air from it. cost me eighty bucks plus coolant. the only other option is replace the heater core.
 
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