Help! No heat! Freexing my arse off!

[500-comanche]

I have an 89 MJ with a 4.0. A few weeks ago I rearended someone and had to put a new rad in it. Everything went fine and seems to work fine. The engine temp seems to be cooling fine. It takes about the same time to warm up as it used to. However, since then, I get very little warm air out of the defroster, and no warm air blowing through the lower heat ducts. If I turn the selector to defrost, moderately warm air comes through the defrost vents at the correct level of flow from 1-4. When turned to heat, no air flows through at any of the levels, but the defrost still works (esentially no difference between defrost and heat settings).

 

What would cause:

1) only moderately warm air to come out of the defroster on defrost

2) No air to be pushed out of the lower heat ducts on heat

[chicofuentes0224]

There's a ball under the passenger side front bumper. It controls some vaccum for the heater controls I think. Make sure that's still there and the two vaccum lines are still connected.

[JeepcoMJ]

you crushed the little black ball that's behind the front right hand side of the bumper. it's called a vacuum canister. without it, you both have a vacuum leak, and no vacuum buildup for to run the heater controls (which are vacuum actuated).

 

also, the reason it's not getting too warm is that you have a heater control valve in the heater lines of your truck, that is operated by vacuum sent through the heater controls. now that this is not getting vacuum, it cannot open. if it cannot open, you cannot get the coolant to flow through the heater core, and therefore, you will not get heat (you'll get just a small amount from energy/heat transfer in the liquid that's sitting there, but that's about it.

 

 

also check that you've bled the coolant system properly...your problem is most definitely lack of vacuum, BUT if you haven't "bled" the cooling system of all air, it may not get warm and may burn up the motor

[Rokhound]

that cool tomorrow i will have heat in the MJ dang thats nice I thougth i would need that ball thing I am glad i saved it I just never new what it did. Thanks for the question and sorry about your truck. :oops: Now I just need to go dig thru about 12" of snow to find it now that should be fun. :nuts:

[undercoverwalrus]

huh, never thought a bum heater could be the result of a vacuum leak... very good to know! having no roof on my MJ sucks when it's misting and 35 degrees out and the heater doesn't work. it'll feel like a luxury car now