I searched this issue, but it seems like most of the results were issues with diesels or the automatic climate control- the rest were never really carried out to completion (thread-wise, meaning no follow up). Bear with me, this is long and detailed...

The truck in question is my e99 with the 5.4 gas, standard heater controls. The truck is always on the road now that college is in session, so I either have limited time to look at it, or it's just not here. I got to my college (just started! Woohoo!) in the morning, and I live close enough that it doesn't fully warm up before I get there anyway. I come home around noon, then the wife takes off for her college- it's after dark when she gets home.

Issue #1- My wife has reported that it's only putting out heat under load. If she lets off the throttle, comes to a stop, or coasts down a hill (even at freeway speeds- it quits blowing heat and blows cool air. She also says that when it is blowing heat, it's just "warm" air, not "hot" air like it used to. She says the temp gauge is in the normal range, in about the same spot it's always been.

I don't know if this problem just started or if it's been slowly degrading, because prior to the cold snap a couple days ago, it hasn't been that cold out PLUS we weren't driving as much prior to this week (before our schools started).

ALSO, last week when it was warmer, I did a little bit of PM to the truck, anticipating the extra driving once school started. From that little bit of PM, I can add the following information:
1) There was no evidence of coolant in the oil.
2) There was no evidence of oil in the coolant.
3) The degas bottle was right at the full mark.
4) All the hoses were in good condition with no evidence of leaks.
5) Truck parks in the same spot every time- there has not been, nor is there now, any coolant on the ground.
6) There is no issue with a leak in the ESOF system: When I switched to manual hubs, I removed those lines and sealed their ports.

Like I said, I haven't looked at it yet, as I didn't notice the issue with my short trip time to school. But since it's dark and cold when she gets home, I'd like to make my time looking into it as short as possible.

Issue # 2- This one I did notice: It doesn't seem like the fan blows as strong as it used to. I still have all fan speeds, but now on high, I can barely feel the heat out of the dash vents if you hold your hand about where the steering wheel is. Last winter, when my hands were cold, I'd aim the two dash vents towards the steering wheel and it'd be like my own personal blast furnace on my hands. Now I can barely feel the air movement.

Last year, I had installed a brand new blower motor assembly, and when I had it apart, the area looked free of debris or obstructions. At the same time, I replaced the blower motor resistor. I would think the resistor would be fine, as I still have distinct blower speeds.

My best guess is that these are two separate unrelated issues. I say that because even if I had hot air all the time, it's still blowing at a reduced volume, AND I would think that even if my blower speeds were normal, it'd still be cooling off when not under load.

Obviously, issue #1 is the most important to me. Last year, you could leave the blower on low and it would still heat the truck fine- it just took longer to do it. Right now in this weather, we can't seem to get the cabin warmer than about 45 degrees. And there's no smiley for freezing and shivering....

 

water pump going bad.. or impeller is damaged. or radiator is starting to clog up.


heater motor going bad... or is loosing power or its ground...
all speeds work but at a slower rate???


Good Luck

 

I just came here because the same thing about the heat, on my wife vehicle, I changed the Thermostat think that! LOL Cold again! Same thing! I was wondering about the water pump going! Nice too see some one else thinks that is a issue! but I do not have a garage! For the fan speed! Does the vehicle have a cabin filter!!!? That would cut down on air flow!!! Had that happen on one of my daughters car!

 

Could be air trapped in heater core or what i've found most likely is the heater core gets clogged a bit so it doesn't perform well. I would pull both lines off and let whatever you can drain out. Then i like to put a funnel in one end and pour clr in and let sit for a couple hours. Flush out with a garden hose afterwards and reconnect the lines. Helpful if you do it with the engine hot I've found. Usually get some gunk out. If thats not it then perhaps working towards the water pump like chuck recommended or even the radiator. I've seen air trapped in the line though that would give you luke warm air out of only one vent. Took some work to get it free had to keep pulling the heater core lines off while the vehicle was running and squishing the upper rad hose until it started shooting out then quickly put it back on the vehicle. Best of luck.

 

Sounds like either a clogged heater core, blend door is not actuating correctly or heater control water valve that regulates water flow to the heater core is faulty. If it is a water pump or radiator problem, you should see spikes in engine coolant temps.

 

I would check the thermostat for fun, those can be problems for heating. easy enough to check and cheap enough to replace.


Other than that my guess is your heater core and or your blower motor is bad.

 

No spikes on the temp gauge- it reads out like it normally does.

 

Did you replace the blower motor with a Motorcraft unit, or something aftermarket?
I put an aftermarket blower motor in my old van and it never had the speed that it had before.

 

Go check the temperature of the two heater hoses when the engine is hot and when a idle. You need to determine if there's adequate coolant flow through the heater core before jumping to any conclusions.

Since the resistor isn't used in the circuit when the speed is set to HIGH, a faulty resistor CANNOT affect the volume of airflow when in HIGH. Scratch that idea.

Does it sound like it's running as fast as it once did?
Does it matter if you've selected MAX AC or one of the other modes?
Can you tell any difference in either the volume of the airflow or the sound of the airflow when switching modes?

 

Thermostat for the heat level.

Check the vacuum system. Make sure it works like it should and isn't blowing out defrost when you select vent.

 

I agree. Just had a similar issue with my 2003 Cadillac. Engine ran at normal operating temp. Even ticked up & down a few degrees while driving every so often, indicating to me that the thermostat was OK.
Did a flush on the heater core only, not the entire system. Heat returned with a vengeance.

 

Sounds like you have a vacuum problem to me. When under load there very little or no manifold vacuum, so a cracked or leaky vacuum line could lose vacuum and cause blend door issues.

How well has the cooling system been maintained?

 

Vacuum problems will be limited to ONLY inlet and outlet selection and usually manifests as the airflow defaulting to the windshield. The blend door is not vacuum-driven, it is operated electrically. There is no indication of a vacuum problem in the stated symptoms.

He has two separate but seemingly related issues, he needs to do the checks I described above.

 

I'll be able to check it out tomorrow, but until then, here's some answers...
I did put an aftermarket blower motor in, but I had great speed up until just recently.

No, it does not sound like it is running as fast as it did. Just a week or two ago, everything sounded and felt normal. You could really hear (and feel) it on high. Now you can't even hear it at all unless you put your ear right up to the vent. I haven't tried MAX AC, so I'll have to get back to you on that one. When you do put your ear & face (or hand) up to the vent, you can hear and feel distinct separate speeds, but what is high now is what low was like before.

All the air directs to where it's supposed to according to where the switch is set. All of it is reduced volume though.

Coolant was changed and the radiator flushed when I got the truck, what- 3 or 4 years ago? Since then, I've checked the level and mixture since then. Level was last checked last week.

Thanks for all the advice- I'll be checking it out tomorrow and I'll report back what I find.

 

if we're voting, I vote pay attention to this. A lot of the advice you've gotten in this thread is not really right.