[font size="1" color="#FF0000"]LAST EDITED ON 04-Nov-01 AT 07:56 AM (EST) by StockMan (moderator)[/font][p]Hello Folks!

My first post to the board.... Man, am I glad I found this place! Tons of great info, and it looks like tons of good people too!

On to the matter at hand....

I have a 78 F-150 2WD pick-up..... The truck has definitely seen better days, but is still in pretty descent mechanical condition, and, I have grown quite fond of it.

The problem is with the heater.... When the truck is started (idling) the blower does not blow at all.... It can sit there and run (idle) for an hour, and nothing.... I can even sit in it, tach it up a little, and still nothing....

After taking off down the road, the blessed thing starts working (blowing) just fine.... This has really become a problem with the cold weather (read: frost/fog on the windshield when I leave for work early in the morning).

I had to put a new fuel pump on the truck today, so while I was at it, I put a new thermostat/gasket on it, and that done absolutely no good at all towards curing the mysterious 'not blowing while idling' problem....

Like I say, after I get five miles down the road, the thing starts blowing just fine.... The air is good and hot, it just takes forever to start blowing....

Outside of basic things, I know very little about mechanicing, and this really has me stumped! Any help would be greatly appreciated!

BTW, It has a 351M, and it does have factory AC (doesn't work) if any of that info is helpful....

Many thanks!

Gene








When I die, I wanna go in my sleep like grandpa did..... Not horrified, and frozen with fear like his passenger!

 

Gene, When you say blow, are you referring to air temp or fan motor speed?
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John

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In the cool still quiet of night you can hear chevies rusting away.

 

o.k this may help mabey not. I have a 351w with factory ac and same problem. Its got an new switch and relay. when I would take off from the house and almost always hit this one bump on our street the blower would kick on. so one day I went under the hood while it was not working and tapped on the blower motor itself with the back of my hand and it kicked on. bad blower.

 

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Is this a Manual A/C or Automatic A/C ?

Manual A/C has a dial for the temp you want and auto just comes on.
The heat in an manual A/C unit waits to a proper temp before throwing power to the blower.

Dennis

78 F-150 429CJ 465,000 KM.(Original Owner)
68 Mustang 289 Sunlit Gold 80,000 Miles(second Owner)
64 1/2,260 Pre-World's Fair Mustang #8092
64 Fairlane 500 S/C,waiting for a 390 4-Spd

If The Girls Don't Find You Handsome,
They Should At Least Find You Handy!

 

Gene,
I own a 1978 F150 2WD and there are no fancy controls on it. If you have a fan speed switch and a toggle for Hot/Cold then its probally your fan motor itself.
KingFisher

 

once it starts blowing, does it continue to blow when you come to a stop again??i thought there was a similar problem with mine one time, come to find out the blower didn't work at all...i was getting the air flow from the motion of the truck...just a thought....another thought...if the blower cover uder the hood is held on by screws (mine is, don't know if all are) take it off...try to turn on the blower, if nothing, give it a little spin to get some initial movement, and see if it works then....maybe the air flow from driving is giving the fan a little jump-start...if that's it, i'd say bad blower motor...

 

If you look down on the passenger side of the dash, you will
see a wire connection going into the plenum (heater box).
this is the risistor, which has a set of coiled resistor wires
on the other side of it. These resistors will loose there values
with age.Which will cause a no-blow from heater blower, useless
you are driving down the road, which blows outside air across the failing resistor and causes the blower motor to run again.
You might have a better chance at a salvage yard than the dealer to replace it.


Dre'
1978 F-150, 460ci(750cfm,Edelbrock Performer,Dynomax Ceramic Coated headers,etc.)Auto-C6,3:70.1 - 9" Posi.

 

one other thing. the bad blower I mentioned is on the bronco, however on the 77 w/ac I had a relay for the blower motor. a little silver box grounded to the lip of the dash just under the passenger side. when it went the blower would not work so I had to jump the harness untill I could find a new one, which the dealer was able to get for me(the only place I could find it).

 

Sorry I haven't got back with you folks sooner.... Been working a lot this week, and I haven't had time to check out anything you guys suggested might be wrong....

I'm off all weekend, and I plan on tackling it either this afternoon, or first thing tomorrow.... I'll let you folks know what I come up with.

To everyone who has inquired, when the truck is idling, there is absolutely no airflow whatsoever.... That includes the defroster, vents, and the floor vents.... When driving down the road, it blows good, warm air.... I can drive 50 miles, and as long as the truck is running (going down the road), it's blowing.... Then when I come to a stop, BAM, it quits blowing, and will not work again until I start driving again.... The guy above who said something about a wiring/resistor problem described exactly what the truck is doing.... Perhaps that will be a good starting point for me.... lol

Once again, many many thanks to everyone who has taken their time to help me out.... It is much appreciated!!!!

Hope you folks have a great weekend!

Gene








When I die, I wanna go in my sleep like grandpa did..... Not horrified, and frozen with fear like his passenger!

 

The last post makes a good point. I've had to replace that relay myself. I believe that relay effect more than just the blower. Your better auto parts store will carry it and it cost me $16.00 in 1994. They may no longer be available.
Secondly, from an earlier post, if the resistor goes bad, isn't there a resistor for each fan speed? so this problem would occur on just one speed depending on which resistor went bad? Could all resistors be bad at once? How does outside air cure the problem? I've lost fan speeds from this but, not all and never saw the truck speed have any effect.
Curious KingFisher

 

so again...what about the air possibly just being from the truck's motion???