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The other day on my 1968 Olds 98, I tried turning on the heater with the engine warmed up, but it was only blowing cold air. The heat button was depressed and the temp button was moved all the way to warm. Where should I start checking to diagnose the problem.
1st thing check your coolant level, and also your coolant mix concentration.
Next- feel both heater hoses after engine is at operating temperature. Both should be hot. If either isn't, either a bad hot water valve or the heater core is plugged.
Make sure the vacuum hoses from engine to vacuum storage ball and ball to heater control panel are connected. You should be able to hear the components switching as you operate the buttons. Didn't you just have some tuneup work done? Shop could have knocked something loose.
The other day on my 1968 Olds 98, I tried turning on the heater with the engine warmed up, but it was only blowing cold air.
A quick question. Did this problem just start? In other words, was the heater working fine yesterday but today it's not? Or has it never worked or not worked recently?
I had a '67 Delta 88 with only the heater, but the basic controls are the same in that everything can be summed up in two words: VACUUM HOSES. There are a ton of them. They all have to be connected, tight, and flexible with no cracks. If any of these is not true on any of them, things won't work right.
Do you have a '68 chassis service manual? If so, dig it out and turn to page 1B-35. I've shown the relevant figure below. Note all of the vacuum hoses. Note their colors. Note the water valve that vintagepne mentioned. Note the vacuum tank that rocketraider mentions. Note the table in the upper left showing the colors of the various hoses attached to the control assembly. If these hoses are original, after 50+ years, they can certainly become brittle and not seal well.
After checking to make sure the heater hoses under the hood are hot when the engine is warm, I would start with the vacuum hoses, and I would start under the hood. Make sure the hose connected from the "vacuum source" to the vacuum tank is present, connected, and in good shape. Make sure there's a hose connected to the water valve that disappears through the pass-through in the firewall. Make sure there are hoses attached to the air door diaphragm. There should be a an orange one and a green one. After these, you'll have to get on the floor and look up under the dash to see the hoses attached to the control assembly and defroster (blue hose) and mode-selector (pink hose) diaphragms.
If everything checks out, I would also check to see that the ductwork is in place. It's not difficult to accidentally knock one off of its fitting as they are just pushed onto their mounting flanges.
In getting the heat to work in my '67 Delta, I found both disconnected vacuum hoses and a completely missing driver's side air hose. The defroster air hoses were present but hanging loose. All the hoses were old, dry, and crispy, and I bought new ones and replaced all of them. Then I had heat! And defroster! I was in heaven!
Thanks to jaunty, Rocketraider & Vintagepne for your help.
Here is the info so far. I purchased the car in Aug 2020. Being summer I only checked the A/C. The only time I knew the heater was not working when we replaced a busted radiator hose and when we turned on the heater we found there was no hot air.
I have attached some photos/videos. The heater hoses are connected. I need to start up the engine, warm it up and then check if they are hot.
The picture of the blower motor shows no vacuum hoses connected???. The vacuum hose from the engine is connected to the vacuum tank and then goes inside the dashboard. Why are there two vacuum tanks as seen in the video.
all these vacuum hoses in the engine compartment are black. I will take pictures of the hoses under the dash later this afternoon and have noted the colors.
Last edited by dukeomer; December 3rd, 2020 at 08:37 AM.
Here is the info so far. I purchased the car in Aug 2020. Being summer I only checked the A/C. The only time I knew the heater was not working when we replaced a busted radiator hose and when we turned on the heater we found there was no hot air.
I'm taking this to mean that, in the time you've owned the car, which is only about four months, the heater has never worked. That answers one of my questions. You say you "checked" the A/C. Did it work? I presume it did. Like the heater, the A/C is also controlled by vacuum. If the A/C works, that says that the vacuum hoses that are specific to it are ok. That would seem to mean that the hoses the control the heater are ok, too, because why would only some of the hoses deteriorate?
What I would do is what we've already said. Check the two heater hoses under the hood. One carries coolant TO the heater core and the other brings it back. Both hoses should be hot when the engine is fully warmed up. If one or both is not, that suggests a clogged heater core or a bad heater control valve. If those hoses ARE hot, then it's on to checking the vacuum connections.
The A/C works fine and blows air through the 3 vents (center, left and right) and able to control the blower speed. I am curious in the picture below what is the purpose of the device with the 3 finger types sticking out that is screwed into the intake manifold.
The picture of the blower motor shows no vacuum hoses connected???.Why are there two vacuum tanks as seen in the video.
An excellent question. Both look old and gunk-covered. I'm wondering if a prior owner "replaced" the original vacuum ball by simply attaching the new one to another spot on the firewall and just leaving the old one in place. It's not easy to see in the photo, but are both vacuum tanks hooked to something? Whatever's going on, what I would do is remove both of those old tanks and install one new one.
I didn't find a vacuum tank specific to your car, but Autozone does show three different ones available. You might take the old one to the store with you and buy the one that matches most closely. You might try other vendors as well.
Of course, one or both of the tanks on your car now might actually still work. You can check it by removing the outlet side vacuum hose and attaching a vacuum gauge to that port. Start the engine to allow vacuum to develop in the ball, and check that vacuum actually develops. If it does, shut off the engine and watch the vacuum gauge. It should hold vacuum as that's the whole point of the vacuum tank---to provide a reservoir of vacuum. If one of the tanks works, clean it up and reuse it.
I am curious in the picture below what is the purpose of the device with the 3 finger types sticking out that is screwed into the intake manifold.
Interesting that there is nothing connected to it. That's a thermal vacuum switch (sometimes also called a ported vacuum switch). I don't know the exact specifics, but I believe there should be three vacuum hoses connected to it. One goes to ported vacuum, one to manifold vacuum, and one to the distributor vacuum advance. The purpose of this is to adjust the engine timing if the engine should start to get too warm. That thing is screwed into a port that senses engine coolant temperature, and it switches, I think, from ported to manifold vacuum if the engine should get too hot at idle as there is no ported vacuum at idle but manifold vacuum is always present as long as the engine is running. I may have some of this backwards, but the purpose of that thing IS to prevent engine overheating at idle.
The fact that it's not connected says that this ability to cool the engine if needed is not working on your car. This may not be an issue if you've never been sitting in traffic on a hot summer day in the time you've owned it. But it might be worth putting in a new one and properly connecting it.
Autozone does show availability of a replacement switch for your car. I'm guessing other vendors would have it as well.
The picture of the blower motor shows no vacuum hoses connected???.
I've been wondering about this. That figure from the manual I posted shows two hoses connected to the "air door diaphragm" which certainly looks like it's part of the blower motor assembly. Are there vacuum ports on the bottom side of the blower motor with nothing attached? Maybe the two hoses that should be attached, one of which should be orange and the other green, are just hanging loose in the engine compartment? Do you see hoses of those colors coming through the firewall grommet?
Here's the relevant information about the thermal vacuum switch from the '68 chassis service manual. (If you don't have one of these, that should be your next purchase.)
Two vacuum ***** usually indicates the car also has vacuum power trunk release.
The vacuum switch Jaunty posted decodes as: D port goes to distributor vacuum advance, C port goes to ported vacuum source on carb, MT port connects to full manifold vacuum.
November 28th, 2020, 12:05 PM
