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Old Dec 7, 2005 | 10:30 PM
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Heater questions

I have a 78 Supercab with factory AC. The AC does't work, but the heater seemed to work fine when I tested it when it was 50-60 degrees out. However, today, it was 20-30 degrees (in south Texas no less!!!), started the truck, let it idle for a couple min, and then drove it for about 15 minutes. However, with the heater on, it never seemed to heat up!

I was just wondering if some of you guys could let me know how long it takes your trucks to heat up and if there are any common ways of improving heater performance.
 
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Old Dec 7, 2005 | 11:47 PM
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Check for plugged Heater core.

Touch both heater hoses to see if they both are scalding hot
If one is really hot and the other isn't,the heater core is plugging.

You have add extra time the colder the coolant gets over night

Come further north for addition training
 
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Old Dec 7, 2005 | 11:52 PM
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check the vacuum valve on the heater hose.
 
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Old Dec 7, 2005 | 11:54 PM
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I don't remember seeing a valve on the 78

Maybe a 75 or 76 ?
 
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Old Dec 8, 2005 | 01:23 AM
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If you have AC, there should be a vacuum controlled heat valve on the heater hose coming from the water pump to the AC unit on the firewall. When your engine is warm, feel the hose in front of and behind the valve. Make sure you have vacuum there. It might be stuck. I used to open and close mine with a pliers as the seasons changed. NAPA sells them. The heater on an AC unit should feel like the Amazon in your cab. If you have to change it, clamp off the hose on both sides of the valve and you won't have to drain anything.That's how I did mine. I don't have AC now but my truck heats up fairly fast. The temperature has been in the single digits at night for the past week. When I start it up, the temp guage starts to move after about 5 minutes.
 
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Old Dec 8, 2005 | 07:39 AM
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Originally Posted by 78f-150Supercab
However, today, it was 20-30 degrees (in south Texas no less!!!), started the truck, let it idle for a couple min, and then drove it for about 15 minutes. However, with the heater on, it never seemed to heat up!
Wow, I just called time and temp and if you hit 20, you are 56 degrees warmer than it is here right now!

Make sure your radiator is full. Low antifreeze will also cause the problems your having.

20 to 30. Tropics I tell ya.
 
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Old Dec 8, 2005 | 08:22 AM
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Originally Posted by Mil1ion
I don't remember seeing a valve on the 78

Maybe a 75 or 76 ?
I don't know about 78's. Definitely on '76's. I would have thought they would be on 78's with factory AC since the core and the evaporator are so close together. They would kind of be working against each other.
 
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Old Dec 8, 2005 | 12:30 PM
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Old Dec 8, 2005 | 12:34 PM
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Looks like a valve's there to me.
 
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Old Dec 8, 2005 | 12:42 PM
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I replaced my vacuum valve with a ball valve. I just shut it off in the summer and turn it back on when the weather is cool. Of course I've also pulled my AC all together now.
 
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Old Dec 8, 2005 | 01:06 PM
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Welp, I was going to go check, and I went out to start the truck, turned the key, and nothing. The seatbelt and brake lights came on, but nothing else... no starter... nothing.

Guess my truck doesn't like the cold weather either and I don't want to go out and find out why right now anyway! *burrr* There were icicles on my truck! Icicles! Down here, we’re thrilled when we get ice cubes from the freezer!

I know 20 degrees isn't that cold to a lot of you, but consider this: 100 degrees is a nice cool day to me!
 

Last edited by 78f-150Supercab; Dec 8, 2005 at 01:08 PM.
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Old Dec 8, 2005 | 01:17 PM
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We're in the negatives now and I'm not happy about it. The cold weather knocked out my car battery last week. 20 degree weather can take its toll on a weak battery so I don't know what condition yours was in but if the battery is alright look at the solenoid on the passenger's side. They are notorious for having problems. If that's the problem you can always do the redneck think and use a battery jumper cable to feed from the battery to the output side of the solenoid just to get it started.
 
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Old Dec 8, 2005 | 02:07 PM
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That why up here we buy batteries with the highest CCA rating.

Mine is a 1000 CCA battery.

A 650 CCA battery will be toast when the temp dips.
 
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Old Dec 8, 2005 | 02:10 PM
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thats the valve i am reffering to in the picture. it was on all the trucks with a/c form 73-79
 
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