C4 1993 Heat Cabin Issue
Thread Starter
2nd Gear
Joined: Nov 2007
Posts: 2
Likes: 0
C4 1993 Heat Cabin Issue
New rookie here. I bought a 1993 corvette recently with 58K and the air conditioning works fine. Its the cabin heater that does not work at all. The blower works fine. Maybe there's a arm that controls the air/heat valve that is bad?? Engine runs at proper temp to provide heat. I bought a used auto control and some kind of valve open/close part that was on ebay the other day just in case. I was just wondering if anyone else has had a similar problem, or a simple cure to suggest trying before going to GM with my wheelbarrow of dollars?? Thanks guys, Plumgone
Le Mans Master
Joined: Apr 2000
Posts: 5,713
Likes: 105
From: Manassas VA
Pull the resister that is mounted on top of the evap. box under the hood. Take a flashlight and look down in the box and you will see the flapper door that controls the heat. Take a long screwdriver and see if the door moves easly, but dont force it. If it does move easly, then the connecting piece that goes from the motor to the flapper is broken. (common problem on the 93)
Assuming it is broke, the part is cheap, but putting it on requires a lot of work. The dash has to be removed to get to it.
I once read where you can switch out the inside heater box to the newer style and they moved the flapper motor to the bottom of the box, instead of on top like the 93 has. You have to reverse the wires going to the motor as well. Otherwise it will open when it is supposed to close and vise versa.
Mine is not a daily driver, so I just manually switch the flapper by use of a screwdriver between seasons.
Assuming it is broke, the part is cheap, but putting it on requires a lot of work. The dash has to be removed to get to it.
I once read where you can switch out the inside heater box to the newer style and they moved the flapper motor to the bottom of the box, instead of on top like the 93 has. You have to reverse the wires going to the motor as well. Otherwise it will open when it is supposed to close and vise versa.
Mine is not a daily driver, so I just manually switch the flapper by use of a screwdriver between seasons.
Racer
Joined: Jun 2006
Posts: 408
Likes: 0
From: Elkton MD
No heat
If the door is working (look into the air box hole after removing the resistor pack and adjust the temp control), and the core is not by passed (easy to see the hoses), then the core is likely plugged.
A plugged core is much easier to fix than the door or leaky core.
To flush the core, carefully cut the old hoses off (don't just pull them as the header pipes may pull out of the core) and put a garden hose alternately against the inlet then the outlet. Don't use too much pressure as the system usually runs under 20psi and house water is usually over 60.
Yes, get new hoses first and plan on a total engine flush with the knock sensors out. Follow instructions for your year Corvette to remove air from the system when refilling.
Good luck.
A plugged core is much easier to fix than the door or leaky core.
To flush the core, carefully cut the old hoses off (don't just pull them as the header pipes may pull out of the core) and put a garden hose alternately against the inlet then the outlet. Don't use too much pressure as the system usually runs under 20psi and house water is usually over 60.
Yes, get new hoses first and plan on a total engine flush with the knock sensors out. Follow instructions for your year Corvette to remove air from the system when refilling.
Good luck.
Pro
Joined: Jan 2004
Posts: 707
Likes: 0
From: Syracuse Utah
The vacuum tubes are plastic and brittle, especially where they are heated by the engine. So, check everything from the engine back. A very common problem is that the vacuum check valve on the right side of the intake manafold cracks and rots.
