No Heat, '03 Ram 1500

Hey guys, I've noticed lately that my '03 Ram 1500 isn't blowing much heat. Either on window defrost, window/floor, or the vents. What I can't understand is why. I've only had the truck for two years and I had a new heater core installed pretty much when I got it. Couldn't imagine it's clogged already, but I wouldn't discount it either. And I've also read the blend door on these trucks can sometimes cause issues. But I'm hoping that's not the issue as I do get a tiny bit of heat, but it's not much of anything. Is there any chance the thermostat could be causing the issue..? Or does this sound more like a rad/system flush kind of thing..? Any and all help is greatly appreciated.

My guess is broken blend door..

Did you go with an aftermarket HC? Aftermarket HC's are known to fail shortly after install, I always use OEM. The blend door could be the cause, you can check to see if you hear it moving at all by taking the glove box out, you'll see a plug going into the servo just to the left. With the in the ON position with the air temp set to the coldest setting, move to the hottest setting and listen if the door pops or makes any movement. You could also have a bad servo which can be diagnosed at the same time.

Does your water temp gauge come up to operating temp normally? If so then your thermostat is ruled out. See if your water level is low, this could mean that the HC is leaking, but you would still get heat.

Thanks for the replies guys. As for the heater core, I have no idea if it's aftermarket or not. My father in law ordered it, so I couldn't tell you. Plus if I asked him he probably wouldn't know or remember. And he would probably give me a little lip saying it doesn't make a difference. He's like that. What I do know is I have a very slow anti-freeze leak someplace. Because I find little green/yellowish spots in my yard from time to time. More easily seen in the snow. Where it's leaking from I don't know. But I recall it leaking when I bought the truck, and still leaking after I had the heater core replaced.

As for the temp gauge, it climbs and stays steady a little bit before the halfway mark on the gauge. So I'm assuming it's working correctly. I just wish I had a gauge that displayed the actual temp reading. I'm honestly thinking it's the blend door, but I'd rather not have to get the dash completely removed again to have to fix it. Already went down that route once with the heater core replacement. Luckily for me the mechanic I bought the truck from did the labor part of the job for free. A 7 hour job supposedly. So I lucked out there. But if I have to get the dash removed again to change or fix the blend door I don't think I'm going to get lucky twice.

Anyway, yesterday was a milder day out. So I got my wife to drive and I checked the heat distribution around the truck. Coming from the windshield defroster the heat was just warm. But when I put the heat on the windshield/floor the results were a little bit different. On the windshield the heat was still warm, but on the floor on the passenger side it felt hotter, (Strange). So I checked the floor vent on the drivers side and it felt cool, or slightly warm. But not as hot as the one on the passenger side. Right there I thought blend door. But i couldn't understand why the heat just on the windshield was just warm. Anyhow, if anyone can shed some more light on this situation with the information I just gave that would be great.

Here's a diagram of your HVAC box so you'll have a little better understanding...


1 - NUT 2 - PASSENGER BLEND DOOR ACTUATOR 3 - NUT 4 - INLET BAFFLE 5 - RECIRCULATION DOOR ACTUATOR 6 - RECIRCULATION-AIR DOOR 7 - DRIVER SIDE BLEND DOOR ACTUATOR 8 - HVAC HOUSING 9 - BOLT 10 - DEFROSTER DOOR ACTUATOR 11 - MODE DOOR ACTUATOR

Your "Mode 2" (#10) door controls your floor/defrost, your "blend door" (#2 & #7) control your cold/hot air flow. If you do not have "dual zone" climate control then #2 is N/A and #7 controls it as one.

As far as the coolant leak goes, does it leak when it's warm or just cold?

Thanks for the diagram. And I do not have dual climate control, so just #7 it is. As for the coolant leak, it leaks if it's warm or cold out. And it's not a very fast leak, I believe it only leaks when the engines warm as I only find a few spots here and there on the ground.

Anyone know where in relation on the temperature gauge that the needle should be sitting at on the '03 Ram 1500 4.7 when the engine is at it's proper operating temp..? Is the one in the following pic the proper operating temp..?

Rambling said:

Anyone know where in relation on the temperature gauge that the needle should be sitting at on the '03 Ram 1500 4.7 when the engine is at it's proper operating temp..? Is the one in the following pic the proper operating temp..?

Click to expand...

The gauge is where it's supposed to be.

That's actually not my temperature gauge, it's an online picture I took from the web. I just wanted to know if the needle position in this picture is representative to where it should be at operating temp. Mine today when I checked it was in between the lower line and the middle line. Then again temps where hovering around -12C today. Didn't try it out on try highway though to see if it would of climbed a bit.

I know you asked about a 4.7, but FWIW, my 5.7 temperature gauge (stock-temp thermostat) has always registered like in the picture above. About the width of the needle to the left of center.

Thanks for the information guys. But I'm going to try and do a couple cheaper fixes first before I venture into the blend door realm. I'm hoping either a new t-stat or a rad flush/fill will cure the problem. I'll keep everyone updated.

Watching with interest. I just picked up my 2003 SLT from my son who has been driving it for four years. Drove from WV to Texas with absolutely no heat. And the temp gage stays in the middle unless I go 70-75 then it climbs to 80%.

Son claims heat was fine the last time he drove the truck. Might take out the glove box this week and see if the blend door actuator is working.

Topping off the coolant to the correct level didn't help. It was a bit low, so I topped it off as per my mechanic's first suggestion. But no luck. So I'm going with his second suggestion and I'm going to get a new t-stat put in and get a full system flush and fill. Hopefully that'll cure the problem. If not, that only leaves the blend door left. I'll keep everyone updated.

Update: I got my coolant system drained, heater core flushed, and a new thermostat installed. And I'm happy to say I have way better heat now. It's not really hot but at least I won't freeze. Mechanic suspects I still have air in the system, and he valiantly tried several technics for a couple hours to get rid of it, but it was giving him hell. So he decided to send me home (40 Minute Drive), hoping the air would work its way out. Told me once I got home to park my truck on a slight uphill grade and vent the bleed valve overnight hoping the air will work it's way out. So I did just that. Beyond that, my thermostat was also part of my issue. Instead of my needle sitting near the half way mark on my gauge, mine would stay roughy in between the middle and first lower line on the gauge. So now it sits were its suppose to.

Now, my only other issue I have is slightly different air temperatures on both sides. The passenger side is warmer, and the driver side not so much. So he determined it's most likely a broken blend door. Another task for another day. But at least now I have heat were I'm not literally freezing my ass off.

Sounds like you may have an air pocket. That's usually what happens. Air in the cooling system will get stuck in the Hester core and cause poor heating.


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So what tenp Tstat is OEM? I just ordered the 180deg because it.was the more expensive of two options and usually I dont like to go for the cheapest option (which was a 203deg) when buying parts.

2003 1500 QuadCab 5.7 4x4

SilverStreak88 said:

Here's a diagram of your HVAC box so you'll have a little better understanding...

View attachment 65255
1 - NUT 2 - PASSENGER BLEND DOOR ACTUATOR 3 - NUT 4 - INLET BAFFLE 5 - RECIRCULATION DOOR ACTUATOR 6 - RECIRCULATION-AIR DOOR 7 - DRIVER SIDE BLEND DOOR ACTUATOR 8 - HVAC HOUSING 9 - BOLT 10 - DEFROSTER DOOR ACTUATOR 11 - MODE DOOR ACTUATOR

Your "Mode 2" (#10) door controls your floor/defrost, your "blend door" (#2 & #7) control your cold/hot air flow. If you do not have "dual zone" climate control then #2 is N/A and #7 controls it as one.

As far as the coolant leak goes, does it leak when it's warm or just cold?

Click to expand...

So when I turn on my AC, air starts blowing and then there is a loud clunk from what seems like under the truck, and then the air gets cold. Is that chunk from one of these doors?

Also there is minimal air coming from the passenger side at all is that the passenger blend door that is faulty?

2003 1500 QuadCab 5.7 4x4

That's what mine did for a couple months before the recirc blend door gave up.