Heater core recommendation needed + another HVAC issue

[DRM500RUBYZR-1]

Leak is absolutely heater core.

HVAC is losing Vacuum.
It goes into default mode, when vacuum drops, sending air to windshield and floor vents. If vacuum supply is good to the programmer, then perhaps the programmer, but more likely the hose that troubles most everyone that you can inspect when doing the heater core.

Marty

[Matt B]

Interesting comment about the vacuum, I'll definitely check that.
Are there any "usual suspects"?

Also, I already was intended to ask you gentlemen about the following - maybe it relates to each other? When I run her at part throttle, I'd say somewhere between 5 and 20% throttle, I hear a hissing noise pretty much from the center of the dash, I'd locate it below the front window defroster outlet.
It's frequency doesn't vary by engine revs neither by how much throttle I apply, amount of throttle only changes the intensity of the noise.
It's pretty loud, very easy to hear. I already checked the engine vacuum connections and fixed the dual PCV grommet. Noise is still there.

As I said, the malfunction of hot air being blown into the car with maximum fan speed (and HVAC in "OFF" mode) happened during extended WOT conditions in a mountain run.

You think these things are the same animal?

[DRM500RUBYZR-1]

VERY Likely the same animal.
Use the Factory Service Manual to identify vacuum hoses and routing for the HVAC supply.
A smoke machine will assist, although if the leak is big, it will quickly envelope the behind dash area.
It is either a, hose, connector, or the programmer itself.
It is there, just search from origination to the programmer.
Others correctly cite the courtesy light area under passenger side dash.
If the hose has been disturbed, and now rests on the bulb, it can melt it.
Most of the time we encounter previous rodent damage.
Good luck, you will find it!

Marty

[Matt B]

Thanks Marty! Very helpful. It's 2 p.m. here so I'll go and check it this immediately. I assume there is a troubleshooting guide in the shop manual.

Now that the dash is out it should be (relatively...) easy to work on that topic.

I'll give an update later on.

[Matt B]

Okay, I just got back from my shop. I pulled the vacuum connector off the HVAC controller (that little retainer disc is AWESOME!!! *lol*) and tested all lines positive. Each holds vacuum as it should, actuators are moving nicely.
Obviously I could not test the vacuum source as engine is not running. Where exactly is the vacuum drawn from the engine? Id like to test the source line for integrity but have no idea where it ends on engine side.

So... No potential noise source found yet.

The heater core housing is nicely accessible now, next step will be to remove the coolant hoses and pull it out 👍

Well... IMMEDIATE next step will be to prepare a home made pizza and empty some bottles of beer. Cheers!

[nelson007]

Hello Marty,

Off-topic a little, but how do you apply smoke into the vacuum line? I have problems with my windshield wiper cover opening on my 1970 LT1. I use a refrigerant vacuum to check the different devices and listen to the hoses, but I am unable to find the leak. I think applying smoke might be my solution.

Thanks in advance Marty.

Nelson

[DRM500RUBYZR-1]

Nelson,
Using any of the available smoke EVAP testing machines ( the more you spend the better they work) simply go to your initial source of vacuum for the combined headlight / wiper system and hook the machine up to that hose and if needed, use vice grips or a clamp to shunt out the working headlight system although at first I would check all as multiple small leaks spell trouble for that darn door.
The machine pushes the smoke through the system.
Then just look for the escaping smoke and there is your problem.

If you find no leaks, first remember to look in the passenger compartment, as that is often the culprit, i.e. headlight switch, overrides etc.

If no leaks are found, start at the manifold and work outwards through each device both in the engine and passenger compartments, until you again find the culprit.
Make sure your hard to find a replacement door mechanism is not binding.
Also double check that the hoses are properly connected. There was a long production run of wiper control valves that had the colored dots on the wrong ports causing the system to work against itself.
Patience and starting at the beginning always seems to find the problem.

Or send it up and we will take care of it.

Go get em!


Marty

[dredgeguy]

Nelson, ROAD TRIP! I call shotgun!

[Matt B]

Sounds like a smoke machine is a must-have. I'll check my local shops if someone sells them. Old cars are never ending vacuum stories...

Talking about vacuum... I'm still looking for the exact source of the HVAC vacuum. Does it have a vacuum canister? If so that's a potential issue...

[nelson007]

Thanks Marty,
Will see you at Carlisle.
Nelson