New Owner 1972 - 250 (Heater Does Not Work)

The heater on my 1972 250 blows air, but it never warms up. A mechanic told me that the heater core is clogged. Does this sound right? Are there other possible problems? If it is the core, are these repairable or do you suggest ordering a replacement?

[gmask]

Originally posted by sail-squirrel
The heater on my 1972 250 blows air, but it never warms up. A mechanic told me that the heater core is clogged. Does this sound right? Are there other possible problems? If it is the core, are these repairable or do you suggest ordering a replacement?

First thing you should check is the heater valve which is on the firewall under the hood above the brake booster. It has three hoses running to it and levers on eithe rside. Your control lines to it may be broken.

I guess the coil fo rthe heater could be clogged.. I dunno how easy it would be to unclog it. I guess if you could detach one fo the hoses onthe valve and force water into with a yard hose it might blow it out clean. Otherwise removing the dash to replace it out or otherwise service it is probably at least an all day affair for the experienced.

[psfred]

Heater core replacement is more like a weekend on the W114/115!

Check the operation of the heater valves, and make sure there is no obstruction in the hoses to prevent constant heat from a stuck valve.

The valves can be removed and cleaned by removing the screw that holds the lever on, removing the snap ring, and then scewing an old Bosch spark plug (the little threaded part on the top of the insulator) in the the screw hole and pushing/pulling them out of the case. They will be all crudded up, for sure. Clean, install new o-rings, and reinstall.

If you still don't have flow, try a couple shots of cooling system flush (the ones with EDTA and citric acid in them), poured directly into the heater hoses, or better yet, longer pieces of hose so that you have some head pressure.

If that doesn't work, try some hot white vinegar -- it will dissolve the carbonate scale. It will foam quite a bit if it works, and you need to keep it out of the block. Rinse well, then run standard cooling system flush in the whole cooling system.

If the heater core is still blocked (no flow, return hose doesn't get hot), you can try stronger acids, but be VERY carefull, you can corrode right through the core!

Also check that the AC door isn't still shut, so that the internal fan runs instead of the heater fan. Heat output is minimal in AC mode, and the AC switch knob often comes adrift, so that you cannot turn the vac switch to the off position. The actuator is beside your rigth foot on teh driver's side, make sure it moves up when you turn the AC off.

Peter