Heater question Caprice '91

Hi guys,

I drive a '91 Caprice wagon and have a question about my heater/AC. When I put my heater on the highest level, I can hear the blower but there is no or very little air coming in the car. Does anyone know where I must look? Maybe the heater valve? Or a heater core full of junk? The same is for the cold air, very little air and almost no cold air coming in the car. Summer is hot now in the Netherlands, so please help. Thanks!

I haven't torn into one of these systems, but typically the way they would be set up is with hot water running through the heater core all of the time, and a mixer door will divert more or less air across it when you want more or less heat. On the other hand, air should blow across the AC evaporator all of the time. This allows you to use the AC to dry the air, then use heat to warm it back up if need be.

If it starts out blowing fine, but later quits, that would be an indication that the evap is freezing over. That could be an expansion valve issue or a blocked evap drain.

If it never blows well, I would get in and check for an obstruction, like an evaporator loaded up with dirt. I might start with pulling the blower motor and looking around with a mirror & flashlight or borescope.

Thanks for your info, the blower works fine but the heater just doesn't get as warm as it used to be. My guess, maybe the heater core that's full with junk? I've replaced the heater valve in the engine compartment.


So maybe my heater core needs to be flushed. Does anyone has a step-by-step explanation how to dis this on a '91 Chevy Caprice?

The 91 heater valve system is unique to the 91. For a 91, make sure the heater valve works. It is vacuum operated, and is a known issue. If you used a junk yard part, it may not work. Other than that, the heater control rod may be disconnected from, loose, or the adjustment may have slipped on the door arm on the plenum.

You may have a clogged core, but that is usually an LT1 issue. I would disconnect the hoses at the radiator, and the heater control valve, because it is a lot easier than trying to disconnect the "quick disconnects", that are actually difficult disconnects, at the core itself. Back flush it through the hose to the radiator. Use a piece of hose to direct any water away from the engine compartment on the valve side.

To examine the heater control door, you must remove the drip pan. This will entitle pulling the carpet back to get to the hidden screw to the driver's side of the drain. The screws will all require a 7mm socket. That is the easy side of it...you must remove the bottom dash cover panel, door sill, and kick panel to get the carpet pulled back.

You should also check the vacuum harness, and make sure you are getting vacuum to the diverter valve under the hood.

Thank you very much, Fred. I have a lot of info to get started. Keep you posted!

The first thing I want to check is the heater control rod. Where is this located?

It goes between the HVAC control unit and a rod end on the plenum to the right of the control unit. It may be a cable with a sheath on it, or a rod. The rod end is bent to make a lever, and is attached to the heat door inside of the plenum. When you pull/push it, it regulates the position of the door.

Everything seems to work, the control unit, the blower. So my next guess is the heater core is blocked by dirt in the last 25 years. Is it easy to flush it? I have never done this before. So alle the help is wellcome. If the flus doesn't work, I have to replace the heater core, I think.

If the air is not coming out of the vents, it is probably junk in the outside of the core. Remove the fan, and get a mirror and flashlight to look inside of the plenum.

I've used the tip that I've found here on this forum and flushed my heater core. I disconnected the hoses near the heater valve. Disconnecting the hoses near the firewall was too hard to reach. But after the flush, which takes about 15 minutes work, the heater core works much better now.
So many thanks guys.

Keep an eye on the heater core for leakage. If it is the original one, it could be close to the end of its lifespan. Try a bottle of Hyperlube to minimize electrolysis in the cooling system.

You should put your zipcode or city/state in you information so we have an idea where you live.

I'll do that, Fred. By the way I live in the Netherlands near Amsterdam

You might put Amsterdam in your location.

I just sent a pair of front gray 91 door panels to Italy.