Engine/Transmission (1998.5 - 2002) Heat still not hot!

[Beach]

I posted a question about a week ago about not having hot air blowing out of my vent's. I have put a new thermostat in, and now I have backwashed the heater core from both direction's and got nothing out that might have been blocking or restricting it. Everything flowed good both way's. To me that mean's the heater core is O. K. because it should be flowing hot coolant. Someone had mentioned that the fin's could be clogged, but would that make that much difference. I don't want to put a new one in if I can help it. If I do have to replace the heater core, can I just remove the glove box and the plate above it to get it out, or do I have more than that to remove. Also I have noticed that the A/C pump is cycling on and off even when I just have it on the blower setting and not defog! The luke warm heat I am getting out seem's to get warm, then cool, it's never steady. Sorry if this explanation got confusing, I'm just lost on this stupid heat issue. Thank's for any help!

 

[SRossi]

Its normal for your compressor to cycle- it prevents the oil from sitting in one spot in the system and the compressor locking up from not being used through the winter. . Is your cooling system full? If your fins were clogged, you wouldnt be getting any airflow out of your vents, or very little airflow. . Im not sure if these systems are heater-valve systems, but if so, maybe check to see if you're heater valve is opening and closing properly. .

 

[Beach]

That was quick! My coolant is full, but I will check to see what type of system I have and if everything is opening as it should. Thank's.

 

[RAJohnson]

Whats your truck?? Fill in your signature so we can see. It helps to know!

Whats your outdoor temp at? How far do you run it after you go some where. Are you running card board in front of the radiator?

 

[tractorface]

Bad news

Got bad news for ya, changing the heater core is a big job. Involves disconnecting the A/C as well Let me try and help you before you get to that point. I had same problem after changing my A/C evaporator core (think that is what its called)

-Get the truck warm and put your hand up under the dash and fel the plastic housing that encases the heater core. Is it cold or warm? To make sure you are on the core locate the servo motor under the dash on the passeger side and run your hnd back and up the side, the core is bumped out a bit. Coolant flows all the time, heat is controlled by a blend door activated by the servo motor you just found. Shop manual has a nice drawing.

-Assuming your core is hot, which it most likely is, you know need to check the servo motor that operates the blend door. You'l probably need a 90 degree phillips to get the rear most screw out. lay under the dash with the truck running and operate the heat control, you should see the servo motor turning (once you have it in your hand. If it turns and your core is hot your blend door is probably stuck.

-Go get a beer and say a little prayer to the truck gods. The blend door sits in a little bushing inside the plastic housing. Mine was "popped" out of joint and made the blend door too difficult to operate. You should be able to grab the blend door "stem" (what the servo drives" and operate it by hand. If you are a bit of a girlie man :-laf you may need a pair of pliers. This would indicate a problem with the door (most likely popped out of the bushing) or that you need more muscle. Either way you are now discovering how bad it may be.

If you have to "get inside and root around" do a search on my name. I had a not so long ago post about cutting the core out of the housing without disconnecting the AC. It can be done but is not for the faint of heart.



Good luck and keep warm

 

[Bpostel]

Yeah, I got the same problem. Heater will not blow hot air. Changed thermostat, nothing. Backflushed heater core, water flowed right through no restrictions. Took servo motor out and it moves back and forth when you turn the temp knob. The blend door spins very freely. What else can it be? This sucks without a warm heater.

 

[Beach]

Thank's for the great info. I'll try to get to the blending valve/door and see if it's stuck. First I have to help get a buddy's 1st gen put back together to plow. I never have time for my own problem's. Thank's again. Bye the way, how do I show my sig, do I fill it out next to my name. I put all that under truck profile.

 

[59Turbo]

Ok, first I'm assuming the truck is a dodge with a cummins. Second, the t-stat is new, did you get one from cummins (dodge dealer) or is it aftermarket? Third, does the temp gauge go to 190 and lastly are both of the heater core hoses hot when the truck is up to operating temp? The blend air door can be stuck, I've seen it before and it is a big job to remove the heater box. What is the actual temp coming out of the vents? Should be around 130F on a med blower setting. Maybe you can move the blend air door manually to see if there is a temp change.

 

[Beach]

The air coming out if I had to guess is around 50 or 60. Not even near 130, I wish. The T-stat is from Dodge and the operating temp is 190. The top hose's are hot, but the lower one seem's to be not as hot, maybe I'm nut's. But yes both are hot. Coolant is full and I don't have anything in front of the radiator, yet. I'm thinking the blending door could be stuck now! Bye the way I figured out my sig for you guy's. Someday I hope to have a book of go fast part's to put on there. :-laf

 

[ACoyle]

For what it may be worth.



1) I read somewhere in this forum, that it is possible to have an air bind in the heater system after opening it. You need to hook a water source to one end and force eater throught it all till all the air is purged.



2) My '99 Ram was very stingey with the heat in the winter. If you are not out on the highway, it may not make enough heat to keep you warm, especially if it is very cold. Mine never came fully up to temp in really cold weather.



3) Somewhere, I sae einter fronts fopr the grille to keep the water a bit warmer. Problem is that really cold air going through the grille cools the engine coolant which closes (Partially) the thermostat. The result is water not warm enough going through the core. If yoiu have access to one of those nifty IR thermometers, measure the temp of the water going into the core.



Hope some of this helps.



AC

 

[59Turbo]

If both hoses are hot to the touch then the heater core should be hot. My guess is either the blend air door is stuck due to the electric motor being bad or the door itself is broken or the heater control head is bad. Try turning the blend air door yourself. You can put a 16 mm wrench on it right where the motor screws on the bottom of the heater box right above the trans tunnel and move it either way. A pen or some other object might have fallen in through the defroster vents and managed to find it's way to the blend air door and wedged itself there in which case the heater box will need to be removed to repair.

 

[tractorface]

Yeah, I got the same problem. Heater will not blow hot air. Changed thermostat, nothing. Backflushed heater core, water flowed right through no restrictions. Took servo motor out and it moves back and forth when you turn the temp knob. The blend door spins very freely. What else can it be? This sucks without a warm heater.

Are you sure it is actually moving the blend door. Should be able to hear it move. It is possible that the rod is just spinning in the door (stripped). That would be a bad deal.



As already mentioned, removing the entire assembly is a royal pain. Been there done that

 

[Bpostel]

The heater hoses are warm not exactly hot. I don't have an infared gun to check them. I took the blend door motor down and I can spin the door very easy, I haven't done it yet with the heater on to see if it changes anything.