No heat after normal engine temp
 

2003 Dodge Caravan CV 3.3V6, approx 101k miles.

Lately after the temp gauge gets to normal, about at the halfway mark the air from heater is cold. I'll adjust the temperature, turning it completely counter clockwise then clockwise, turn the system off/on. Eventually after about 10 minutes there will be heat, at the normal temperature. I don't know if making adjustment and resets to the system is what activates the heat, or it just comes on for another reason.Then, there may be several seconds of cool or lukewarm air again - then back to hot as it should be. Once underway with sustained hot heat it's fine for the rest of the ride. After parking for several hours the same no heat condition can occur again after the temperature gauge reaches the normal halfway point.

Up until last week there was no trouble. The coolant level is normal. Could it be the thermostat not opening? I wouldn't think so since the temp gauge appears to indicate as it always did. Once underway today after the heat became normal it was good for the rest of the 25 minute trip.

First check the supply hoses for the heater core when the engine is up to operating temperature. If they're cold or luke warm, there is a flow problem to the heater core and it will need to be flushed.

Check your radiator coolant level. It can be low where it will run at the normal temp but not have enough to flow to the heater.

The other day when driving for a while I checked the hoses, the were hot but at that point the heat was fine. The coolant level is between min and max. I have an appointment to have the coolant flushed next week (It's a company van). The last 2 mornings slowly moving the heat control from cold back to hot eventually produced heat. Sometimes it'll briefly get cool for a few seconds, then back to hot. After that happens it stayed hot for the rest of the ride.

Here's a couple other things to check:

1) Check for a cabin air filter - I'm not finding any definitive info on whether or not your caravan should have a cabin air filter so you'll just have to look for an access panel for it either under the passenger side dash or behind the glove box. Sometimes a severely restricted cabin air filter can cause the control module to do some weird things with the actuators. I can't really explain it - I have a few theories of my own but I've not had the time or resources to test them. I can only speak from the experience of seeing this problem and a new cabin air filter somehow fixing it.

2) If the cabin air filter isn't an issue, the problem must be with either the control panel or the temperature blend actuator. Since you're going to have the cooling system flushed, you can ask them to check for DTC's in the HVAC module. That could give you some direction.

Never thought of the cabin air filter. Will look into that. I'm thinking it could be the blend actuator. Sorry I have to ask, but what are DTC's? Today once the heat was present it was consistent for the hour + ride. Ironically didn't need much heat today, but got an early 7" of snow last night.

Thanks for the tips so far.

As scargi01 said above, you need to check the coolant level in the radiator. The level can appear normal in the over flow reservoir, but check low in the radiator.

I did check the radiator the other day - it appeared full but will check again. Once the heat is on for a few minutes it's plenty hot from that point on.

I see you have a Grand Caravan with the 3.3V6. We had a 2005 Caravan 3.3 in our fleet. It was rusted, but running fine when we had to retire it at 300k miles. I tried to upload a photo of the odometer but it was huge. Didn't see a re-sizing option. Anyway - it seems like a great engine. Up until the colder weather recently I was averaging about 22mpg. Mostly highway - but still very good considering it's loaded with equipment.

DTC = Diagnostic Trouble Code. Most people only know them as related to the check engine light, but almost every car these days uses modules to control just about everything, including HVAC. In most cases you can pull a code when something isn't working right.

You're not wrong in believing the blend actuator has something to do with the problem - it most certainly is the reason for the heat to be switching back and forth - the question is why? Off the top of my head, here's a list of possible reasons why the blend actuator isn't working properly:

-Blend door sticking/dragging due to debris (possible result of cabin air filter issue)
-Faulty actuator
-Actuator wiring problem
-HVAC control module faulty
-HVAC control module wiring problem
-One of the passenger compartment temperature sensors is faulty
-One of the passenger compartment temperature sensors has a wiring problem

Are you noticing a pattern? Not only do you have to determine what component is responsible, but you also have to diagnose the related wiring because an open or high resistance on a power, ground, or signal circuit can cause an actuator to malfunction. I've seen it done several times, and made the same mistake myself, of seeing a problem such as this and assuming it just needs an actuator. 9 times out of 10 it will fix the problem - but when I'm being paid to make sure it's fixed right the first time, it's not good enough to just start throwing parts at it. So if I suspect the actuator is at fault, I first make sure sure all the signals to and from the HVAC module are correct, then I replace the actuator. If I find a problem with the wiring, I'm diagnosing and repairing that before replacing the actuator.

I believe it was years ago with my first car, a 1967 Chevy Caprice that the blend actuator was accessible. I vaguely remember a similar situation to what I'm having now, and the no cost fix was to move it manually for no flow to the heater core in the spring/summer - and move it back to the heat position in the fall. That's why I'm thinking it's the actuator - but like you said it may not necessarily be the actuator itself. It could be the voltage going to it.

The pattern I can establish is if I move the heat control many times slowly from hot to cold, and back to hot - I will eventually get heat. Then, it may go to cool again briefly - I'll move the temp control again from cold to hot. Once it's hot for about a minute it stays that way for the rest of the ride - anywhere from 10 minutes to over an hour. Tried the same procedure during lunch yesterday without moving the van - let it warm up to almost normal temp (halfway point on the gauge) but that did not produce heat.I then drove it about a quarter mile - got some heat. Don't know if driving is of any significance.

I wish I could see the actuator, I assume it's in the dash. Another probably unrelated issue I've noticed and definitely confirmed yesterday after filling up is the fuel economy has dropped significantly lately. I'd usually get approx 340 miles out of a quarter or between a 1/8 and a quarter tank. Yesterday I filled up around that mark at only 303 miles.