HEATER ACTIG WEIRD

[barrett86]

alright guys im back to another problem that ive had SINCE it has gotten cold outside. during the summer lol my heater would get so hot it would burn me when my hands get close to the vents, now when i use my heater if i idle for awhiel the heat will come in shortly for like a min or 2 then go cold then hot then cold but if i romp it while in park still to like 4- 4500 rpms instant hot. now while driving its always hot until i come to a stop light if i sit for awhile it goes cold, then when i drive off it heats back up, could this be my heater core going out, if so how hard are they too fix and where are they, and how long of a project, if not then *** is going on hahhhahha. thanks for the help.

 

[Seabronc]

What year is the truck, and do you have A/C?

>-

 

[barrett86]

86 bronco and yes i have A/C but its doesnt work cuz its not charged.

 

[Seabronc]

It sounds like a problem with the vacuum to the controls. Attached is a diagram for you. The feed is from the main vacuum tree to a check valve and from there to a vacuum reserve tank and to the controls. the line is a small black vacuum line that goes in on the passenger side of the truck.

Good luck,

>-

 

[barrett86]

ok there is 4 hoses behind the controls is the black wire behind there

 

[Broncobill78]

Fred's probably right to suggest it's most likely a vacuum problem because that's how the temp is controlled thru the blend door. Just as a wildcard though how's your coolant level ? I've had trucks with pinhole radiator leaks that caused me to lose coolant, not enough to make it run hot in cold New England weather but enough to starve the heater core & cause it to alternately blow hot & ice cold for no apparent reason. It's probably a vacuum problem but checking the coolant only takes a moment.

 

[Seabronc]

Ditto on Bill's comment on the coolant. It could also be that you only get flow through the core when revved. That could be coolant level or maybe a pump problem. Have you ever flushed the system? Could be slightly clogged, or even air stuck in the core. You could put a flush T in the return line hook up a short piece of hose and nozzle to bleed air and check the flow from the core. Air in a heating system will make it either fail all together or operate erratically. If you have plenty of coolant, then you could also try reversing the hoses on the core, sometimes that will clear a clog, but if it is a clog I'd do a good flush of the system and refill with new stuff.

Good luck,

>-

 

[barrett86]

how random is this, my brother goes to skill center (auto tech) and he came home today and told me the same thing, and i was going to hop on here and ask about coolant but i got busy, i think coolant could be low, how do i check though, i always thought fill it up til it gets to the top of the hole right. or is there a better way. thanks guys.

 

[barrett86]

BTW I TOOK A BUNch of pics of things i need answers about, ill post them up later on today after i sleep. lol.

 

[Broncobill78]

how random is this, my brother goes to skill center (auto tech) and he came home today and told me the same thing, and i was going to hop on here and ask about coolant but i got busy, i think coolant could be low, how do i check though, i always thought fill it up til it gets to the top of the hole right. or is there a better way. thanks guys.

Just take of the radiator cap. Please *don't* do this when it's hot, you'll scald the **** out of yourself. Once it's cold open it up & take a look. Should be right up to the neck. Is there anything in the overflow bottle ?

 

[barrett86]

nothing in the overflow, and i cant see any fluid at all under the cap. so its low on coolant, and yah ill get more. lol.

 

[Broncobill78]

Yup, sounds like that's your problem. Refill it & let us know if you get your heat back.