afgunn

Have a 94 LT1 and not getting any heat. The hoses going to the heater core are hot. Also, supply air from the AC/Heater only comes out the floor and defrost - will not change. Are these problems related?
What is the problem(s) and where are the parts located?
Thanks in advance!

Cliff Harris

Do a check on the HVAC diagnostics:

afgunn

Sorry, no blinking led above the OFF button. I really appreciate the video.

Some more info. With the interior temp set to 90 (max) the AC runs when the air supply is set to recirculate or bi-level (buttons 3 & 4), but not when set to lower or upper delivery - buttons 5 & 6. With the key in the on position and engine not running, when each of the air supply buttons is pressed I can hear something like a relay clicking. All I have for now.

Ozzstar

What do you mean by "air supply button"? This isn't a technical term I'm familiar with. Are you discussing the FAN speed buttons UP and DOWN?

enventr

This should be a sticky. Great info thank you

Smokeysvette

I AGREE PLEASE PUT THIS UP AS A STICKY!!!!!

afgunn

The buttons that determine where the air will be delivered. Sorry, I do not know the terms used, I did not have my owner's manual, and even it uses the designation on the buttons and does not name them. This is why I numbered the buttons left to right starting with the OFF button. No, not the Fan speed button.

aDigitalPhantom

Just remember that this does not work with manual climate control.

afgunn

Thanks, but as stated above, I am getting no error codes. I have checked some of the functions according to the video, but still not able to discover a problem.

I think it may be it is a vacuum problem. Will try to check.

Smokeysvette

Also make sure you don't have any air in the system. Like in another post and I had a similar problem and turned out to be the black expansion tank. My heater hoses were also both hot too.
The problem I had was it leaked antifreeze (very little) at the neck but mostly it let air in the system and therefore no heat.
Yes, your problem may be different because I didn't have the blowing of air just out the floor and defrost outlet. That could be a possible vacuum leak causing this.
Hope this helps.

afgunn

Yes, it helps! I have even thought that the heater core could be clogged allowing no/little coolant through. And, I may have more than one problem!? I hope to narrow it down a little tomorrow. Thanks again.

afgunn

Can anyone point me to where the vacuum line for the heater controls goes through the firewall on my 94?

Cliff Harris

My car is a few years older than yours, but I can't imagine that it would have changed. It goes into the wiring harness and through the firewall through the bulkhead feedthrough located behind the passenger side head.

This picture from Agent 86 shows the vacuum line (sticking up behind the red wire) and how it goes into the wiring harness (the bulkhead feedthrough is on the far left):

enventr

I do not know about the heat problem but the air just flowing on the bottom could be the "T" plastic valve under the rail covers. Inspect that part. That part sometimes breaks .Very inexpensive
Good luck

john6277

I have helped many with this common C4 issue. My 95 coupe had the same symptoms and I checked out the basics as you have.
The problem is probably the damper door electric actuator motor on the the heater/ac box under the passenger knee bolster. To check it out easily from under the hood, take the small top plate off the heater box near the fan motor housing. You will also see a electric harness attached to this plate, but it will allow you a look into the heater box and the metal damper door (about 4X6) that separates the A/c front side from the back heater core in the back . Move the heater controls and this damper door will probably reveal is does not swing with A/c and heat settings. This is why you have little or no heat - it is stuck.
Next is to remove the knee bolster by exposing the fuse panel cover and carefully pulling the bolster towards you. The bolster has 4 plastic tabs on the front and these are quite brittle so go slow. Now at the bottom of the heater box you will see the heater temperature valve (Ecklers #51595, $100). Remove this with 2 bolts and now see if the motor is seized up by trying different heat- A/c settings. I'd bet yours is frozen from internal corrosion like mine was. Now turn the shaft that goes into the heater box and swing the damper door. You should now feel heat.
You may want to check out my postings on the C action forum site (John6277) on this topic.
One final note, don't be temped to buy the $50 cheaper Dorman motor as it is a very poor fit. All the best to you Merry Christmas.

afgunn

Thanks much! It will probably be a few days before I can get a chanceto check it.

afgunn

Thanks much! It will probably be a few days before I can get a chance to check these things. These problems or no vacuum seems to be my problem. I do not have heat nor can I change where the air comes out.

afgunn

Where is the "C action forum site"?

afgunn

I am beginning to believe that I have a clogged heater core plus air supply control failure. I had the car at a muffler shop today and when I came to pick it up it had sat for 30 min to 1 hour. As I first drove off it was blowing moderately warm air. As I drove it got cooler and cooler until about 8-10 min later it was cold. So, I am thinking blocked heater core and while it sat it had time to heat the heater core. I am concerned though that if it is blocked and I reverse flush it, the next thing that will happen will be a LEAKING heater core and all the fun that comes with replacing that!

Thoughts please!?

Cliff Harris

There is a restrictor in the heater hose that sometimes gets clogged up. Check that area.

Look under the passenger side fuel rail cover for this guy (vacuum check valve -- about $4 at any auto parts store):