89 f250 5.8 heavy duty 4x4

Where is the heater control valve i think it is stuck open because when tune the temp to cool it still blows hot air not cool air from outside. seems as if the heater is always on.

I know my A/C dose not work but still should blow cool air out from the vent position right?

Thanks in advance!!!

 

If your application uses a control valve, I'm not 100% sure if the 89 does, it will be in one of the heater hoses between the engine and firewall where the heater hoses go inside the truck..

I know the later trucks don't use a water control valve, they use a "blend door" to route the air through or around the heater core.

 

There is no control valve on this vintage truck it's all done with the blend door and it sounds like yours is stuck closed.. which is uncommon. The door is controlled by engine vacuum and to get to it you first remove the glove box and then the heater core cover and it should be visible.

 

Hey Paul, does the 89 have the issue of the white vacuum line that goes bad like the 90's do?

Another quick question. If the vacuum is lost, does the blend door default to heat or cool? Or does it just stray where it was the last time there was vacuum?

 

I thought the temperature control was operated by cable and only the fresh air door and vent selector were vacuum operated.

My '87 uses a cable for both the temperature control and vent position selector, but uses vacuum to control the fresh air door - I know that changed, but I'm not sure in what year.

 

'89 and '90 trucks should be the same though we know how that goes.

I know there is at least one vacuum actuated device in the heating system on these trucks but I couldn't tell you with 100% certainty what it is now, but in any case I bet the OP's problem is with either the vacuum or cable operated components inside the heater box... or with the controls themselves.