Broken Heater - Just in time for winter!

So I ran my heater for the first time this year only to find out that it's not working. The fan is blowing, but it's cold air. I know very little about car mechanics, but my first thought was to check the fuse box. I found a 25 Amp fuse for the AC, which I figured was possibly the culprit. The fuse was fine, so referred to the owner's manual and service manual, but I can't find anything on troubleshooting the heater.

My wagon is a 1990 Oldsmobile Custom Cruiser, and I'm planning a trip out of town for Thanksgiving. It would sure be nice to have heat.....lol. Does anyone have experience in this area or could maybe point me in the right direction? And please excuse my ignorance. I know enough about my wagon to change oil, tires, and bleed the brake lines, but that's pretty much the extent of my knowledge. Any help would be greatly appreciated.

 

I'm not familiar with the specifics of your 1990 Olds.
The heat is supplied by hot water from the engine.
There is often a vacuum controlled valve on the heater hose where it passes through the firewall. Check that the vacuum hose is connected. Manually apply vacuum to test the valve.

Either the heater core is not getting hot water, or the flapper doors in the ducts are not switching to pull warmed air from the heater core.

 

Start small- is the coolant level where it should be, either full cold or full hot depending on the engine temp.

On the Olds 307, the Heater Control Valve is mounted on the rear of the intake manifold, passenger side, with one heater hose going into it, and then screwed into the intake manifold itself. There is a vacuum line going into it, which is plastic tubing. Make sure that is not disconnected as mentioned.
With the engine hot, touch each heater hose, with the mode selector on heat, temp selector on hot. Is there a significant difference in tempature?

With the car running, move the mode selector through all the modes (vent, bi-lev, heat, etc.) with the fan off. Do you hear anything moving behind the instrument panel, like a mild thump? You want to hear that noise. Is there a light hissing perhaps when you move the selector?
When you move the tempature control from cold to hot, do you feel the usual resistance, and is there any change at all to the tempature?

Knowing all of the above will help pin down where to focus, whether on the controls, the heater control valve, or perhaps you just have a clogged heater core.

Hope this helps you a bit. Let us know what you find.

 

Thanks for the help so far, guys. I'm gonna tackle this over the next couple of days and see what I can find out.

 

Okay, I just went outside and checked everything out. The coolant seems to be fine; I've never had any problems with overheating. I flushed the radiator and replaced the coolant this past spring, so that shouldn't be the problem.

As for the heater control valve, I had to use Google because I had no idea what I was looking for. Anyway, I finally found it. I could see where it threads into the intake manifold, but I'm confused about the vacuum line. There is a 3/4" tube attached which runs to what I believe is the heater core. Is this the vacuum line? Also, there is a very thin plastic wire (appears to be electrical) which runs out of the top of the heater control valve and then meets up with a whole mess of wires near the firewall all the way to the left on the passenger side. These seemed to be securely connected.

Next, I cranked the heat all the way up and touched the two hoses coming out of the heater core. One hose is about 3/4" in diameter and runs to the heater control valve, and the other one is slightly thicker in diameter and runs toward the front of the car (I presume it connects to the radiator). Both hoses were very hot to the touch, and I did not notice any significant difference in temperature between the two.

When I got inside the car and turned the fan off, I noticed light hissing and clunking noises coming from behind the instrument panel when I switched between vent, AC, bi-lev, heat, and defroster, which I hope is a good sign. Are those noises related to the heater control valve?

Sliding the temperature control back and forth from hot to cold didn't change the temperature at all. I put my hand right under the air vent and I couldn't tell any temperature difference between the 65 and 85 degree settings.

One other thing----I read in the owners manual that having clogged vents can affect air flow for the heater. I'm parked right under a tree, and my car is covered in leaves. I tried to pull some of those out from where the hood meets the windshield, but I didn't notice any difference. Could that be enough to cause the heater not to work?

Anyway, thank you so much for all of your help. It is greatly appreciated. And again, I apologize for my ignorance. Bear with me, I still have a lot to learn. Thanks!

 

Yes, you'll definitely want to get all those leaves out of the cowl area between the firewall and the windshield. Much of that fall foliage has no doubt made it down into your dashboard and heater box where the fan and all those flapper doors and ducts are. I noticed when I changed out the cabin air filter(s) in my Silhouette, most of what was in those filters and floating around in the filter box was a match to the leaves, twigs, nuts, berries, and general mess sitting on top of the cowl area.

Both hoses hot generally means your heater core is flowing ok and is not plugged up. If the supply line is hot and the return line warm or cold, you would have a blockage of some kind. So I'm willing to bet the problem is in the dash, one of those flapper door things or a vacuum line. Or it is possible the wire that controls the flapper door position (this is connected to the slider for the temperature on the HVAC control head) has become disconnected either up at the control head or down by the door itself.

This was the problem I had in 2001-2002 with my '88 Plymouth Colt Vista. That car only had heat, no AC, it was from Idaho. And it was SO EASY to figure out my no heat problem. I moved the temp slider, and there was a linkage on the outside of the heater core's box. I could see it didn't move. So I checked and sure enough, the wire was not connected to the temp slider. Slipped it in, replaced the circlip, bingo, lots of heat!

 

Ok, it looks like you made some progress. Yes, you are correct about the heater control valve. That hose does feed into the heater core, and what looks like a wire is the plastic vacuum line I mentioned, it is colored with a black rubber end where it attaches to the control valve. That mess of wires is yet more vacuum harness for the climate controls.
Determining that both hoses are hot means we can rule out a clogged heater core as previously mentioned.
Those hissing and thumping noises when moving the mode selector is perfectly normal and what you want to hear. This indicates the flapper doors are functioning to the selected mode.
You indicated no change when you moved the temperature selector. That would lead me to believe that either the other end of the control cable has become disconnected inside the instrument panel, or there is a blockage of leaves and debris inside the system. What does it feel like when you move the selector? Hard to move, or normal/very easy?

All that debris needs to be removed from the top of the cowl plenum at the base of the windshield. If you can't get it all by hand, I suggest a car wash vacuum cleaner. While you are at it, if you can- take a flashlight and look down through the grill and see if you can observe any accumulation of debris. If it has been in there long enough, it will look like dirt as it is most likely decomposed leaves, etc. The leaves that you are seeing on top are not causing your problem directly, but years of it in the system can block those flapper doors.


No need to apologize for your lack of knowledge. This is how we all learn, so ask away!

 

Great to see you guys helping griswold out. And, I agree....since everything seems to be operating correctly I would think that the lever for heat's cable is disconnected or broken. Happens often enough in old cars.

 

Thanks again, guys. My next approach will be to get rid of those leaves. Originally, I was thinking of maybe a shop vac (which I don't have), but a car wash vacuum would be perfect.

As far as sliding the temperature switch, it offers very little resistance and I can easily flip it from 65 degrees to 85 degrees. I assume that resistance would indicate blockage by leaves and whatnot?

Should I follow the vacuum line through the cluster to it's connection point? Is that the other end of the control cable you were talking about? If so, where should I start looking to find the detached cable?

Thanks a million, guys!

 

Heavy resistance would indicate a stuck/rusted/gummed up wire or a jammed blend door. Moderate resistance is normal. Minimal resistance means it's probably disconnected down at the blend thingie. No resistance at all means it's probably disconnected up at the HVAC control panel.

 

I couldn't have said it any better.

I would definitely start with the cable connection for the temperature behind the control panel. As far as your vacuum line question, that serves to operate the various doors, so I would not spend any more time on that at the present.
Do you have a diagram of the HVAC system? If not, I can scan those pages out of my FSM and send them to you if you like.

 

I would say there is minimal resistance at best. It slides very easily. How should I proceed? Thanks!

 

Nevermind, this answered my question...lol. I do not have a diagram of the HVAC system, but maybe I could find something on Google? If not, I would really appreciate it if you could send me what you have, BigBird. Thanks guys!

 

You might be able to find something on Google, but I am not certain.
I am at the office right now, so it will be tomorrow morning before I can get it scanned in. You're quite welcome.

 

Gris...this could be easy

if i recall...your dash controls are 'vacuum operated'...if one of the lines are shot... then its just a case of finding which 'lever' on the actual 'heater box' is the HOT AIR to COLD AIR flap...you could then just reach under the dash...grab the lever...give it a push...and walla walla....HEAT !!!

worst case scenario....the 'heater core' is plugged?