1969 Mark III – “Steam” coming out of vents

Hi Bill,

Can you shed any light on why I have steam coming into the cabin through the vents that normally distribute heat, IE, windscreen and dash vents. The AC/heater has not worked properly for years, and it does not make any difference when I move the heater controls. The coolant level drops when this happens.

Thanks

Gerry

Hello Gerard

It is good to hear from you as it has been quite a while. 

Your vapour and steam leakage into the cabin area sounds strongly like a classic heater core leakage in a large amount. Correct diagnosis is of course very important. One way to diagnose this fault is to carefully clamp each of the heater hoses positively shut with a clamp and then operate the engine normally to carefully observe if the leakage has then stopped after a reasonable short period of time. Another way is to disconnect the hoses at the heater core and attach them together in order to bypass the heater core. If the vapours and steam leakage has stopped with either of these tests, the heater core must then be suspected,removed and bench tested. A bench test should be performed by a good radiator shop locally in your area. If they cannot repair the leak and or your core is found to be too rotted out we will be able to supply you with a good tested and guaranteed used one.

The other issue that you briefly mentioned is not uncommon and can be caused by any of several “atc” control problems. One is that over the years if some one has tampered with and upset the factory control setup. Another is that if vacuum is lost to the controls, the system will default to maximum heat/defrost as a safety measure. Lastly and most common is that the “atc” box and or power servo has failed and will need to be bench tested and overhauled. We are well equipped with parts, equipment and knowledge to perform this.  

When this ac/heat climate control option is working as designed it is great operating and welcome feature. Please let us know what you discover and decide to do.

                                                               Good luck

                                                                     Bill