93 FZJ80 Heater Problems (1 Viewer)

[wbrad99]

Done a lot of research and looking for advice regarding my heater.

‘93 FZJ80 - My front and rear heaters blow hot for about 10 seconds then become lukewarm. A/C blows cold and all blowers, modes, and vents work. Heater control valve on firewall is new and opens / closes properly. Back flushed heater core (I have not noticed the passenger floorboard get wet). New thermostat. Pulled most the dash to replace air mix servo motor, no improvement. The cable attached to air mix servo motor moves when I change the temp. Inlet and Outlet heater hoses are hot after running heater, so I would like to assume the heater core is not clogged. I’ve also burped the cooling system and ensured coolant levels are good.

Looking for any advice or direction for where to look next. Any tips are appreciated!

 

[RC51]

How long did it take you to change / get to the servo motor?

Have you checked the FSM that is specifically for diagnosing the AC? Its a separate document.

 

[wbrad99]

How long did it take you to change / get to the servo motor?

Have you checked the FSM that is specifically for diagnosing the AC? Its a separate document.

Took a few hours over two days, wasn’t fun but not as bad as I expected. I checked it out but did not find much addressing my issue.

 

[NeverFinis]

Both front and rear heaters you say?

I would get an infrared thermometer gun and measure the temperature of the heater pipes on the firewall. Make sure it is hot on both sides of the valve.

To me, if both heater cores are doing this, this is either the new valve on the firewall, or something odd is happening at the water pump. There is blockage some where other than the heater cores.

 

[wbrad99]

Both front and rear heaters you say?

I would get an infrared thermometer gun and measure the temperature of the heater pipes on the firewall. Make sure it is hot on both sides of the valve.

To me, if both heater cores are doing this, this is either the new valve on the firewall, or something odd is happening at the water pump. There is blockage some where other than the heater cores.

Thinking you may be onto something with the water pump. Heater pipes both get warm / hot to the touch. I have never had any overheating or reason to suspect cooling issues, but not sure where else to look besides the blend doors, which I would love to avoid.

 

[TheBussman]

perform a block test to see if the head-gasket is leaking and putting exhaust gas in the cooling system. A small leak can do things like this and still run OK, not overheat. The factory water pump has a metal impeller, I don't think it's possible to slip. If it's a aftermarket water pump anything is possible.

 

[Squash]

So,
First off crawl under PS dash look up and find the lever which should move according to where you set heat/cold. This needs to stay where you decide. You are looking for the lever and threaded aluminum rod.
Picture of lever is laying on your back looking up...