76cutlasscoupe

Just bought a 76 cutlass coupe. Heater nor ac works. But when driving, especially for a longer period the area around mu feet and legs gets very warm. There is a slight hot air coming from the vents and the cabin just heats up in general. The hot light isnt coming on so im assuming the engine isnt overheatng... is this normal?

redoldsman

When you say the heater isn't working, do you mean the blower is now working? I am not sure but I think the heater temperature is controlled by a control valve on the top of the engine near the rear. If it is like a 72, it screws into the intake manifold. That could be the problem.

Octania

"do you mean the blower is not working? "

Yeah, it sounds like the HEATER part is working just fine.

Look at the right rear corner of the intake for the thing with the heater hose attached to it. Is it just a nipple, a house plumbing fitting, or a vacuum operated valve?

76cutlasscoupe

76cutlasscoupe

Is that what youre talking about there in the back?

76olds

My 76 also produces heat at the floor even with the heater turned off. I read an article that stated this set up was to allow air in the cabin at all times back in the day. Nothing wrong with the heater or vents. From what I can see in the picture the heater bypass/control valve has been taken out. You will feel heat coming thru in the summer months as well no worries its all good.
What is wrong with your heater ? You say it doesn't work?
Hope this helps
Eric

76cutlasscoupe

Not sure.. i just bought this car yesterday. Nothing you do to the a/c control panel produces any results. It does have an a/c compressor so at one point it worked. Im figuring something wrong with the control panel or the blower

76olds

I'm not very good with all the little part names, but you could check what I believe is the heater solenoid which is the first small box on the passenger firewall that wires plug into. Also check at the heater box below the fan it could be unplugged these cars are known for noisy fan bearings. This would be a good start.
Hope this helps
Eric

joe_padavano

No, the temperature is NOT controlled by the heater control valve. That design stopped being used in the early 1960s. That valve is only used on A/C cars and is normally fully open. It only closes when the A/C is in the MAX COLD position. There is a mechanically operated temperature blend door in the HVAC box under the dash. This is what controls temperature, blending hot air from the heater core with cool air from outside. If this is not working properly, you'll only get hot air. Also note that the other flapper doors inside the HVAC box are vacuum actuated. The system is designed such that if you loose vacuum (due to a broken hose, for example), the system defaults to routing air through the defroster and floor vents. Verify that the vacuum hoses are correctly connected and operating properly.

redoldsman

Interesting. My 72 Cutlass blows cold air through the floor and defrost and not the AC vents. I know it is a bad diaphragm that controls one of the doors.

Octania

Well, I see a vacuum operated water control valve there in the intake with a heater hose connected to it.

It looks newish.

They are made in two flavors, at least. One allows flow of juice when vacuum is applied to the control port; the other shuts off juice when vacuum is applied. Inverse logic.

If that is a replacement part, it may be the wrong logic. Our '68 98 family car had this issue, and it gave NO heat as a result. One thing you can try is removing that control vacuum line [plug the hose] and see what happens. Not better? Run manifold vacuum to that control port on the valve and "hotwire" it with full vacuum, see what that does.

But, first, take a peek under the dash, look at the controls, see if anything is just obviously disconnected or has been messed with.

joe_padavano

The break points in the temp control valves are 1970-older for the full size cars and 1972-older for the A-body cars. The older valves are normally closed and open with vacuum applied. The newer valves (including the one that SHOULD be installed on the OP's 1976 Cutlass) are normally open and close under vacuum.

In all cases, temp is controlled by the blend door in the HVAC box. The heater valve only serves to block all heat during MAX COLD A/C operation.

Fun71

Sorry in advance for the thread hijack.

Joe, I wanted to verify you posted this correctly. I bought a heater control valve for my car and it is open with no vacuum applied (still sitting on the bench and I just checked its operation). All metal valve, part number stamped on it is H25-124, RANDO, COLO USA.
Rock Auto shows a Four Seasons 74602 valve for my application and the info shows that valve closes with vacuum. 1970 application shows a 74601 and vacuum opens that one.

joe_padavano

You can check this in the A/C section in the CSM. I verified in the 1972 manual, which also shows that the full size cars work opposite from the A-body cars that year. Vacuum is applied to the valve to open it for heat on the earlier cars. These normally closed valves are no longer common, so it would not surprise me to see the incorrect later style valve installed.

You can also check to see when you get vacuum on the hose going to the valve. There should be vacuum on the hose in the HEAT position, but not in the MAX COLD position. This is opposite of how the newer cars operate.

76olds

[QUOTE=Octania;887285]Well, I see a vacuum operated water control valve there in the intake with a heater hose connected to it.

It looks newish.

You are correct Octania thanks for correcting me, I didn't look at the pic good enough. Sorry to the OP for not seeing that.
Before I removed mine from my 76 I had the heater hose from the rad going to the lower part of the valve and the upper heater core hose went into the top of the unit. Not sure how his is set up. Initially it appeared to me as the vacuum advance can, my mistake.
I really think the previous owner just unplugged the fan because of the noise, either at the fan motor itself or the little solenoid on the firewall. Just my thoughts .

Eric

Cutty77

Do you know where I can find a diagram for the vacuum hose routing for a 77 Cutlass with AC? I can only get air flow out the floor, it won't switch to the dash or defrost vents. I had a couple broken lines when we pulled and replaced the engine. Thought I got them back together right.

joe_padavano

Chapter One of your 1977 Chassis Service Manual. There are about a dozen on ebay right now, starting with this one for $8.

76olds

As Joe mentioned a manual will help out tremendously, in the mean time check the connections coming from the ball on the passenger fender. I had the same problem and I found that is was the vacuum line going from the ball to a junction on the intake.

Hope this helps
Eric

Freddie1088

I have the same issue on my 1976 Oldsmobile cutlass supreme how did you resolve the issue? Thanks

Freddie1088

Just bought a 76 cutlass coupe. But when driving, especially for a longer period the area around mu feet and legs gets very warm. There is a slight hot air coming from the vents and the cabin just heats up in general.