Fan blows out of vent on right

[farrisl]

I am the recent proud second owner of a metallic blue 73 240z. I am amazed at how complete this car is. I live in Kansas and while this car is not going to be a daily driver, I still want Airconditoning. I plan on buying the compressor upgrade kit from MSA.

Before I can upgrade the airconditioner I have to fix a problem with the vents. When I have the heater controls set to vent and turn the fan switch to low all is well. Air blows out of each vent in the same volume. When I switch the fan to medium the air blows out the same for an instant, I hear a muted clicking noise and then all of the air is blowing out of the right vent. While my passenger might really appreciate this I know I will feel slighted.

Everything else about the heater controls seem to work normally. Air blows out the defroster, heater etc.

I have searched the forums for something similar to this problem and can not find anything.

I suspect that the dash will have to come off, but I did not want to do that unless necessary.

Any help will be much appreciated.

[EScanlon]

First off, welcome to the club.

You mention that the left "eyeball" looses the air to it when the fan is on medium, I presume on High as well. What about the center vent?

A note of explanation here: The 240Z ventilation system, when on the VENT position, will only blow air through the two "eyeball" and the center vent. In order to get air out through the defrost or floor vents the heater must be set to HEAT.

I'm not sure about the A/C operation, but I presume that it would do it in the VENT position. (I've never owned one.)

Now, that you are hearing a noise and then the left vent is cut off, I think points directly to something loose inside the heater box that is in turn blocking the left tube. Either that or something in the left tube. That is the reason I am asking about the center vent. You should almost be able to see directly into the plenum that divides the air between the center and side vents.

2¢

Enrique

[farrisl]

Enrique,

Thanks for your reply!

Yes, it is both the center vent and the left vent that loses air. Yes, both vents are affected on high also.

The defrost and floor vents work fine and just like you said only when the heater panel is set to heat.

I will take a flashlight and look inside the center vent and see if I can see something.

I will post another reply to this thread when I have taken a look at it.

Regards,

farrisl

[EScanlon]

I'll wager that it's the flap gasket inside the heater box that has come loose from the flap and is now flopping around and closing off those two vents.

Fast explanation of the system:

The Vent Flap located at the firewall either allows air in from the vent in the Cowling bucket or not. If not, it recirculates from the cabin. This then feeds into the fan motor housing which sends the volume of air into the plenum of the heater. Inside the heater there is a second flapper valve that either directs the air THROUGH the heater core, or out the top to the center and eyeball vents. (Note, this is why it is impossible to get warm air out the center or eyeball vents.) There is a third set of flapper valves that either release the now warmed air out into the "room" or cabin, or allow it to be forced out the defrost tubes.

Both flapper valves have a foam backed "leatherette" gasket pad that is glued to the face of the metal flap. When in the closed position, the flanges of the opening push against the foam gasket and seal off the air. After 30 years, either the foam backing or the adhesive holding it down will have corroded off the leatherette gasket. The two "doors" at the bottom of the heater box usually only had foam insulation which died very soon, so not too many people have seen them.

In your case, I think it may be that the gasket has separated completely and flops around closing the two openings you mentioned.

The fix? Well, there are those that claim that they can remove the heater control box without removing the dash, and those of us who think they're either 2 ft tall, or are triple jointed.

Since I am not a slim slender ballerina, I have to remove the dash. Once the dash is out, pinch off the Water Lines in and out, being careful not to spill and remove the heater box, disassemble and glue down the gasket or repair as needed. Sorry, this is the ONLY way I know to fix something inside the heater box.

One note, if you do remove the dash, do yourself a HUGE favor and do the following:

Take the time to disconnect, and reconnect electrical connectors. Just this simple act can sometimes eliminate potential circuitry problems.

Remove, inspect and replace any and all instrument illumination bulbs. Why not? It's a bear to get to them otherwise, and if any of them look dark, now's the time to replace and get brighter gauges out of it.

Wash out all the HVAC tubes with some grease cutting soap, if in the U.S. I recommend DAWN. Inspect for cracks and repair accordingly. Just this step alone will make your car smell 1000% better.

Before replacing the dash, take a look at the firewall. Just below the windshield you'll note two rubber plugs. One on either side of the center line. Make sure those plugs are there and in good condition. Believe it or not, lack of these will cause you to get intermittent splashes of water into the cabin, and they are one of the hardest to diagnose as the culprit of the strange puddle that shows up after driving hard in a rain storm.

Take a look at your Fresh Air Vents. They should operate cleanly and with no major effort on your part.

Lastly, take a look at the condition of the rubber elbows and kick panel rubber bushings they go through. You might just find a leak about to happen. Remember, these tubes DRAIN the cowl bucket area. If the hose leading to the exterior is shot, the water just flows onto your feet.

Anyhow, hope some of this helps.

Enrique Scanlon

[farrisl]

Enrique,

Thank you so much for your help. I really appreciate your anticipating other things I should look for with the dash off.

Regards,

farrisl