Hello, I'm new to the site and look forward to posting question from time to time.

My problem lies in the Heater unit itself. I warn-up the engine and turn the heater on, for the first 5 seconds it puts out great heat ,then slowly gets cooler, till it is cold air. I have flushed the raditator and the engine block. The hoses to the heater coil is very hot. Oh, I replaced the thermostat also. A raditator shop told me that they thought it was the door flap. I did find part of a small spring clip on the floor below the heater. So I need to know is it hard to take the heater cover off and what to look for when I do? If I could find a drawing of the inter parts of the heater - that would help a bunch. Later the butcher
P.S. I have a 92 Ford Van 5.0 L

 

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My first guess would be a partially blocked heater core. It gets hot but when you blow air across it it cools off. If it were the blend door, I wouldn't think it would be hot at first.

By the way did you actuallly mean you have a 5.0L in your Aerostar?

Another possibility is that the water pump is not pumping full force. What does the temp gauge read?

 

Oh man, I almost started drooling when I saw the 5.0 Liter part

 

Sorry, when I use the word van - it means E-150 , Aerostar is a Mini Van.
So I have a E-150 Ford Van 5.0L V8 302 . Also both hoses going to the heater coil are hot, and it does blows hot air for the first 5 seconds. f1butcher

 

I suggest that install a NEW heater core.

 

you have a blocked heater core it results from lack of cooling system maintance

 

Thanks for the info. I believe you nailed it. In August my air stopped blowing cold air, and with not much extra money , I rolled down the windows and made it through the summer. So do I need to get the air conditioning fixed or can I just get the heater coil fixed? Thanks , Butch

 

same problem with my f250. when the truck is driving the heat is great but when i sit idle for 20 min it starts to cool down. the dealer told me the heater core is partially blocked. is this true? why cant they try to unblock it instead of installing a new one? i dont know if they checked the water pump but the engine does not over heat. i kind of hear a high whistle for a few seconds when i give it gas or let off.could that be some kind of vaccum leak? and could that be causing the bad heat at idle??? Please help!!! they want $350 to replace heater core and i am not sure that is the problem. they are known for guessing at fixes.they replaced brake pads and calipers for pull to the right when hard braking only to find when it need inspection the drag link was bad. but didnt admit they were wrong about the pads and calipers!!!!!!! now the after replacing that the truck no longer pulls! PLEASE HELP

 

My fix was to replace heater core. The heat coming out of the vents is now 140 degrees and steady. Hope this info helps you.

 

did you have the same problem? heat was fine when driving but at idle it got cool?

 

Yes, then in about a month or so,it slowly progressed to very little heat. My 1989 E-150 wasn`t hard to change out the heater core. Hardest part was disconnecting the heater hoses from the engine compartment. Once I got the right tool for it, the rest was pretty easy.

 

my 2000 f150 heater doesnt blow hot air my temp gauge is higher than normal my fan clutch seems to stay on more and my radiator don't seem to be circulating also my heater core hoses arent hot. My question is where do I start at fixin the problem theremostat or core. thanks, MEGAFLEX

 

Warm the engine up, stop the engine.

Then disconnect the exit side of the heater core house

Connect a length of hose into a large jug (a few gallons)

With the rad cap open (no pressure in system), measure the flow rate through the heater core... if the flow out is not greatly fast, then:

A) try back flush the heater core (disconnect other hose, feed hot water through it).

B) failing that, replace the heater core.

Before you do B), make sure that there is not a vacuum operated door that is closed or not operating properly causing no hot air to go from the core to the car interior.

 

Ok,

I have a somewhat similar problem, driving the van with it just on 'vent' the temp gauge goes a little past half way. I turn on the AC, MAX and the temp drops to half way.

My question, how do you check the vacuum module that operates the heater door ?

Is there a relay for that function ? If so, where, which one is it ?

Thanks, Greg