RestoVette

Thought this story might help prevent a problem for somebody else doing a mid-year restoration:

During the rebuild and total restoration of a 65 roadster, I installed a brand new heater core. While on a short drive after restoration was complete (eight months later), steam started spewing out of the defroster duct and condensing on the windshield. After spending a couple hours removing and disassembling the heater box, I found that corrosion had perforated the hose connection tubes of the new heater core. I returned the core to the local Corvette parts dealer and the manufacturer replaced it on warranty. Even though the engine coolant was still nice and clean, I flushed the system and put in new coolant when I put it back together.

Seven months later, while on another short drive, steam again started spewing out of the defroster duct and condensing on the windshield. After spending another few hours removing and disassembling the heater box, I again found that corrosion had perforated the hose connection tubes of the new heater core. I returned this second “defective” core to the local Corvette parts dealer and the factory again replaced it on warranty. And again, even though the engine coolant was still nice and clean and there appeared to be no corrosion problem with the rest of the system, I put in new coolant (and for insurance, some anti-corrosion solution) when I put it back together.

After this second occurrence, I obviously had concern that it might happen again. As a pre-emptive measure, after a couple weeks I drained the system coolant and pulled the heater hoses so I could inspect the heater core connection tubes. To my dismay, when I pulled the heater hoses from the core, I saw enough green copper oxide to tell me the problem was still there. While pointing this out to my wife, I inadvertently touched a metal screwdriver to both the engine and a heater core connection tube......and drew a spark! In checking with a meter, I found that the heater core was at +12V potential. Obviously, there had to be a short or mis-wiring to cause the heater core to be electrically "hot".

It took me just a few minutes to track down the source of the problem. When I had installed the clock in the non-conductive fiberglass dash, I inadvertently hooked up the hot (+12V) side of the wiring to the case of the clock. (The clock was not polarity sensitive and would run okay with reversed connections.) The clock case was mounted in a metal bracket that also mounted the metal heater controls, which in turn conducted the +12V to the heater core. With the heater core at +12V and the engine block at ground and semi-conductive cooling water between them, I had set up a natural plating bath (electrolysis) that rapidly destroyed heater cores!

To fix the problem, I simply reversed the wires at the clock. I did not change the heater core this time, since the damage to the third heater core was still minimal.

6T7L71CPE

Well, I found out someone hooked up my clock backwards a different way. Although my heater core had the same symptoms I assumed it was just old. I just removed it from the system. I had a small plastic ear plug case (sidepipe car) that had a short cap retaining chain on it (military issue). I had it draped over one of the heater controls on a drive one day and all of a sudden it POPS and falls off smoldering on the carpet. I then found that there was 12+ between the two parts of the control because the clock connection was wrong.

Allcoupedup

Thanks for taking the time to share your lesson.
Brian

Viet Nam Vett

Wow...That's a new one..... Quick..!!! Every one get your Volt Meters ..run out and measure your Heater core..!!!!

Thanks for passing that one along. I'll add this to my Trouble book.. :cheers:

Rogs65

Yikes!!
that would have been a tough one to diagnose..
Thanks for the insight.
Roger

Paul L

That is a useful and informative post! As I have a new clock, and will be installing it in the spring, which of those two terminals is "true" hot. And what is the colour of the wire going to it?

Guest

It’s the one black insulator underneath.

Paul L

Thanks! And the hot wire is black or orange?


[Modified by paul67, 7:48 PM 1/19/2004]

JohnZ

Orange is hot, black is ground; unless someone has messed with the terminals in the "L"-shaped connector, that's the way it goes together (orange/hot on the insulated terminal, black/ground on the other one). :thumbs:

Paul L

Thanks John.

Kid_Again

good info, thanks