[MDv6man]

Hey all

Like the title says...I'm at my wits end with this no heat condition in my wife's 94 RMW. At this point, almost everything has been replaced... (at least that I can think of). Here's a brief timeline of events and what has been done and replaced.

Back in March, I drained the cooling system and added straight water with the Prestone flush. I also pressure washed the coolant reservoir. Soon after that, the water pump gave up its ghost and it would pump coolant out rather quickly.

I took it to a mechanic friend. We replaced the water pump, thermostat, coolant sensor, and were stumped as to why it would continually boil over after 30 minutes of idling. This led to replacing the radiator and radiator cap as well as the steam pipe.

I got it back a few weeks ago. Pulled the drivers side knock sensor and drained the system and installed a Delphi (AC Delco) heater core. At that time I pulled the electric actuator for the temp door. It seemed to move as it should with the temperature change buttons.

Still no heat...

After about 3 days of driving, the plastic T and coolant restrictor snapped...I replaced them with universal Motormite pieces. Got her running, but no heat.

Finally, this past weekend, I got into the heater diagnostics using the shop manual. Everything seemed to be in spec...I cleared the two stored trouble codes and they have not come back.

Any thoughts would be appreciated...I'd like to be able to drive the thing this winter without freezing

 

[seanu]

If you have hot flow in and out of the core then I would think that it was internal with the vents..maybe the inside flap (that switches from a/c to heat) is broken? I had this happen on an old Surburban, and had to fix it...

 

[Gregg-O]

As stated , if both heater hoses are hot, and the core is new, you have an issue with the vents/doors in the 'box' under the dash.

 

[The Fooser Guy]

As stated , if both heater hoses are hot, and the core is new, you have an issue with the vents/doors in the 'box' under the dash.

'Not always so Tonto'. "New means 'new', it does not mean 'good."

Just had a buddy go thru this senario last winter. Both heater hoses were warm/hot, all the under-dash heater/blend doors worked, the heater core was installed correctly (not just laying on top of the lower cover panel -with no air circulating thru it - because some idiot broke off the brackets that hold it up in place - I've seen that one too), flushed the core both ways, etc., but still no heat on the long drive back from FL to St. L. in the dark of winter.

Turned out that his brand new heater core was 'short circuiting'. The water was going into the core, thru a small portion of the core and back to the block. I'd be for checking for this before installing a 'new' core (rig a way to run hot water thru the core at the sink and be sure all of it warm?) . I could also see this happening if you flushed a core and got some crud stuck inside it.

HTH.