Heater core recommendation needed + another HVAC issue

[Matt B]

I just got back from feeding the beast at a local gas station and realized that my heater core is most likely leaky. Symptoms are fog build up at the windshield after stopping the engine and moisture in passenger footwell. So... Seems obvious, no?

Rockauto offers a variety of cores. Can anyone recommend any of these? Or are they all the same cheap Chinese crap?

Second issue I have is with the HVAC. Here I found 2 symptoms. First: sometimes, usually upon starting the car, the system sort of "resets" itself to 24 degree celsius, all automatic mode and in few cases also turns on the rear window defogger. Last weekend this happened while I was driving with the system turned off (targa roof was off, so no airflow needed).
Second: with the system in "Off" mode under hard acceleration (not sure if that is relevant) the fan started blowing full power, outlet air was maximum hot. As I don't expect an emergency engine cool down function I suppose my HVAC controller module (??) has an issue.

No LED lights are flashing, no codes present either. What do you think?

[GOLDCYLON]

Originally Posted by Matt B

I just got back from feeding the beast at a local gas station and realized that my heater core is most likely leaky. Symptoms are fog build up at the windshield after stopping the engine and moisture in passenger footwell. So... Seems obvious, no?

Rockauto offers a variety of cores. Can anyone recommend any of these? Or are they all the same cheap Chinese crap?

Second issue I have is with the HVAC. Here I found 2 symptoms. First: sometimes, usually upon starting the car, the system sort of "resets" itself to 24 degree celsius, all automatic mode and in few cases also turns on the rear window defogger. Last weekend this happened while I was driving with the system turned off (targa roof was off, so no airflow needed).
Second: with the system in "Off" mode under hard acceleration (not sure if that is relevant) the fan started blowing full power, outlet air was maximum hot. As I don't expect an emergency engine cool down function I suppose my HVAC controller module (??) has an issue.

No LED lights are flashing, no codes present either. What do you think?

Matt I believe they are all Chinese crap however you are correct your heater core is toast. The passenger footwell wetness and the moisture out of the defroster vents is the symptoms of a failed heater core indeed.

No idea on the HVAC a problem but the controller is indeed suspect

[Dynomite]

Originally Posted by Matt B

I just got back from feeding the beast at a local gas station and realized that my heater core is most likely leaky. Symptoms are fog build up at the windshield after stopping the engine and moisture in passenger footwell. So... Seems obvious, no?

I concur as always with GC

Many Heater Cores for C4 Corvettes on Ebay.

Post 135 - Replacing the Heater Core and Heater Hose Connection

[Matt B]

Thanks for sharing this! The guide looks very helpful and thoroughly made!
I'll also check Ebay though it's not as easy for me to deal with as many sellers don't ship to Europe or at least charge a fortune for it. Rockauto doesn't...

2 more questions: is an aluminum core to be preferred over a brass version? In my understanding aluminium is first and foremost a CHEAP solution. But is also a GOOD (in terms of fit and durability) solution?
I remember from replacing my Lincoln Mark III heater core that the replacement part (aluminum, too) was about 1/2 inch thinner the the original and doesn't properly seal against the walls of the housing. I had to add a lot of alien material and also do some modifications to the housing to ensure proper fit and air blending.

Second, when reading your guide - is it really that much easier than just pulling the dash? I removed my CDM twice and I know that even with all the skills gathered during the first attempt working down there is a PITA due to the absolute lack of space.
Due to the total lack of personal experience: is this really a shortcut that saves significant working time (which is not paid off with bleeding hands and a mental breakdown )?

[dredgeguy]

Matt, one word of advice, whatever heater core you get test it first before install to be sure it does not have any small leaks. We tested mine with air pressure and it was good. It took several of us almost 8 hours during Wazoo maintenance day to do mine. We pulled the dash. As the guys took out screws, I would bag and tag them so we put them back in the right spot. Pulling the dash was stressful, I remember it would not come out and Nelson said, "just yank on it". On the count of three, pop, it came out about the same time my heart jumped out of my chest. Still cannot believe it all went back together without any broken plastic clips and without any rattles. No left over parts is good!

[Matt B]

8 hours by professional corvette guys... That sort of scares me (and answers the question whether doing the job without pulling the dash might be more time efficient...)

Pressure testing is likewise a good advice! Thanks, I'll definitely do.

For the moment I'm considering to bypass the core and fix it later that year. We have STUNNING weather and it's a shame to not run the targa ZR because of a broken heater core she definitely doesn't need...

With that I could also invest some time to go through all the pesky noises my dash produces...

[secondchance]

Originally Posted by Matt B

8 hours by professional corvette guys... That sort of scares me (and answers the question whether doing the job without pulling the dash might be more time efficient...)

Pressure testing is likewise a good advice! Thanks, I'll definitely do.

For the moment I'm considering to bypass the core and fix it later that year. We have STUNNING weather and it's a shame to not run the targa ZR because of a broken heater core she definitely doesn't need...

With that I could also invest some time to go through all the pesky noises my dash produces...

Matt,

Having done this work on dredgeguy's 92, to remove and install a new heater core in one piece will require dash removal.
I think a short cut would be to cut the protruding supply and return line at the outside bulkhead for easier removal. New heater core supply and return line can be cut just enough for splicing back on after installation. This strategy might negate wholesale disassembly of the dash.

[Matt B]

Thanks, Yun. I'll definitely take this into consideration. I already started today by taking out the drenched carpets. I ordered a "TYC" replacement core from Rockauto. Most likely it's china stuff but I will have my OEM piece fixed by a specialized radiator welder so I can put it back in at a later stage (if ever needed).

So later this week I will pull the dash... Get s**t done

[Matt B]

So, upper dash is out. Went surprisingly well, less than 1 hour incl. permanent cross checking the shop manual and searching for tools

Now that I'm in there... What can I do to improve my rattling, squeaky little diva? I remember that someone mentioned a GM Service Bulletin that covers squeak and rattle in early ZR-1. Can anyone share this? Thanks!

[secondchance]

Originally Posted by Matt B

So, upper dash is out. Went surprisingly well, less than 1 hour incl. permanent cross checking the shop manual and searching for tools

Now that I'm in there... What can I do to improve my rattling, squeaky little diva? I remember that someone mentioned a GM Service Bulletin that covers squeak and rattle in early ZR-1. Can anyone share this? Thanks!

I am not aware of the bulletin. My experience with 91 and 94 has been squeaks and rattles originated from places other than under the dash.
I would examine and look for suspects since there already. Combination of foam wrap, zip ties might help.
Also, check the condition of vacuum connections at the HVAC controller. Again, since you already have the dash out.