Another no heat problem

Ok guys...I'm working on my 91 estate wagon. I had great heat one day then nothing. I noticed my temp guage wasn't hitting its usual spot,I checked the t-stat...it wasn't working right so I replaced it. My fan works great and I can switch from defrost to floor with no problem. I'm not getting heat anywhere. Because it happened suddenly and had heat before. ..and there is no coolant smell inside, I ruled out the core.

There is a valve in the rear passenger's side of the engine compartment that controls the flow of coolant to the heater core. It is operated by vacuum from the manifold under the glove box, which is controlled by the HVAC head unit. It is a 91 only item.

I recently replaced the hcv, the vac line is attached, I also dropped the panel under the glove box,started the car and played around with the buttons...no change..no heat. I also took off the air splitter behind the ash tray and discovered the door that's inside....kinda lost as to what to do next. Any help is appreciated!

Does the door move when heat or AC is requested? Is there any blockage of the heater core? Feel the hoses for heat.

When I pushed the door up, the air felt like it was all going to the defrost and when it was down the air went to the floor. I haven't had much luck with it going through the dash vents but there is some.I'm still not getting heat though. It's rainy and cold here right now and don't have a garage. I'm going to work on it more tomorrow.

Both sides of my hc are hot, the temp is good. I disconnected the negative side of the battery to reset...and the hcu went through a countdown. ..twice and then kicked on but still no heat. I ordered a blend door actuator.

Did you check to see if the blend door was working first?

Fred..I'm flying blind right now using the process of elimination. I know its behind the glove box..I haven't pulled it out yet but everything else works good.

The process of elimination is also called troubleshooting. The problem is always the last thing you check. Once you have found the problem, you stop and fix it, so no more troubleshooting is necessary.

I've looked over a few videos and it looks like the trim that goes across the front of the dash is going to have to be removed in order to pull the glove box so I can get to the heater core. Thanks for any help

You can not remove the woodgrain from the dash panel without damaging it, because it is permanently attached to the dash face. The dash face does not require removal to access the lower part of the HVAC plenum. 

The heater core itself is accessed from the bottom of the plenum. There are 6-7 screws holding the drip tray to the bottom of the plenum. One is hidden between the firewall and drip tray. It is difficult to get a socket on. Some have used a flex drive, but I prefer a combination of 7 mm socket, extension just long enough to reach, and a 1/4 inch adapter to a hex drive, with a hex drive ratchet similar to the side post battery ratchet. The firewall bends back close to the tray, and there is a minimum space to work. You will have to pull the carpet back to get to it. You must remove the threshold and kick panel to pull the carpet back. If you put the seat all the way back, or remove it completely, you will have more room to work. Be careful when removing the tray, it is easy to crack where it goes through the firewall, and if cracked, will cause large amounts of water on the floor. Remember to remove the elbow on the engine side of the firewall. When reinstalling the drip tray, remove the seal, and apply silicone sealer to make a new seal. Make sure you put ALL of the screws back, especially the one between the firewall, and drip tray. Put some silicone on the post for the screw that goes through the bottom of the drip tray.

Step-by-step instructions pasted from an older post on removal of the drip pan.  I used a flexdrive because it was what I could cobb to reach the hidden screw from hell.

Good luck.

Quote :

Removed the passenger seat for more room.  Remove the ashtray.   Remove the cover beneath the dash, passenger side carpeted kick panel, and rocker trim, and glove box.   Removed the brace rod beneath drip pan (one 10 mm nut on firewall, one 10 mm bolt on dash end).  Peeled back and folded over the carpet for more clearance.  Remove the 10mm bolt securing the lower brace along the bottom of the dash panel.  It's just to the left of the door seal (I removed the rocker trim piece to expose this bolt head).  Once this bolt is removed, and the brace rod is removed, you can pull the lower edge of the dash rearward about 1/2", which you definitely need to do to get the drip pan out in one piece.  Removed the 7 hex-head screws holding the drip pan in place (5.5 mm socket).  You'll need a 5.5 mm open end wrench, as noted above, for screw #5, and a gooseneck flex extension and 5.5 mm socket is what I used to reach the PITA screw #7 that you can not even see on the firewall side (about 1.5" to starboard side of screw #6).

I used Permatex Ultra RTV gasket maker (a tube and a half was needed).  Cleaned out the grove.   The old gasket had dried out on the firewall side, which is where it was leaking.  Laid in a generous bead of RTV in that groove, and immediately replaced the pan and replaced and tightened the screws about half-way.  Waited one hour and then tightened the screws fully and put it all back together.  

I'm still trying to figure out how the glove box comes out. It looks like the trim panel that covers the entire front of the dash has to be removed

I did the above on a 1996 Caprice wagon. I'm not sure if everything is screwed together the same on the 91 RMW. Fred would know.

I'm pretty sure the glove box needs to be removed to reach the blend door actuator...I need some heat.

Working from memory and the attached photo here, as the car is still in storage, but I think the glovebox on the Caprice is held in place by four screws that are readily removed.  The glovebox door and glovebox well are one integral unit, so everything is removed as one unit.  The dash framing the glovebox remains in place.

Thanks! Due to covid, the county I live in is about to be on lockdown for a month, so I will have plenty of time to play with my ride...lol...do you know if the moonroofs have drain holes? I have a leak coming from there.

The entire roof rack and load bar system drains, if it leaks, drains to a channel underneath the edge of the headliner, adn drains towards the rear. The vista-roof glass does not have it's own drain system. Is it leaking around the weatherstrip?

I'm not sure. My headliner gets wet when it rains.

A. Where does your headliner get wet? There are channels at the B and C pillars to drain the area if it gets water in it. You can check for leaks by putting dishwashing liquid around the trim, and using air pressure (air gun) on the inside to see if it produces bubbles on the outside. One of mine had a leak at the driver's rear corner of the vista glass.

B. You do not have to remove the whole glovebox to get to the blend door actuator. I just looked at the FSM, and you must remove the dash face (do not try to remove the woodgrain from the dash face). It should be behind the ash tray assembly. First you must remove the ash tray assembly, and the glovebox door. The FSM says to lower the steering column to facilitate removing the dash face. The temp door should be in the middle, right in front of you.

Before you remove everything, try calibrating your system...Run the AC for at least 30 seconds, then run the temp down to minimum for 3 minutes, then up to maximum for 3 minutes. If that does not cure the no heat situation, then take it apart.

My headliner gets wet over the drivers door. Also across the front of the headliner where it meets the windshield

I would take the headliner down, and check for rust in those areas. The front glass is notorious for having rust under the top of it, and you may have a rust through at the B pillar.