When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I'm working on my 1970 250 Cutlass S A/C and Heat. At some point the dash was taken out the car but wasn't reconnected properly. After some work I have connected all the vacuum lines along with everything else that was disconnected. The heat was working this winter after I connected the blower motor and changed out the relay but I could never get the hot air to blow out of the vents. Which lead me to investigate and I noticed the door that controls the air flow was not opening. I didn't mind that at the time because at least I had heat. So to the issue at hand, upon inspection I noticed the reason I had heat was because the heat hose control valve did not have a vacuum attachment on it. Basically was a bypass connection from the engine to the heater hose which allowed the water to always flow to the heater core. Great in the winter and sucks in the summer. I replaced the heater control valve and connected the vacuum line to it. This weekend the temperature dropped and I tried the heater and had no luck. The vacuum for the heater control valve and the one that opens the air flow control door are not working which leads me to believe that I'm not getting vacuum (wild guess), I followed all the diagrams and everything is correctly in place. So I'm wondering if it's something I'm missing............ Any tips on troubleshooting?
Yes two things on this:
1- I've seen heater control valves open and close when vacuum is applied. You need to see if you have the right one. I have a 71' but aside from the increase in size from 1/2'' (70') to 3/4" (71'-72) they should open when vacuum is applied. One I ordered from Rock Auto closed when vacuum was applied.
2- Not sure on the 70' but there is a Tee at the heater control panel that goes in between the round manifold and the straight ports for the 71' 72' years. The 70' control panel is slightly different. A shop assembly manual has the vacuum diagram in it for the control panel, hard to find but it's in there. I'd send you a pic but my manual is a 71'.
What you are missing is the fact that that's the diagram for a full size Olds, NOT for a Cutlass...
I know that this is not the diagram for my car I just posted it to reference the job at hand. Here is the correct one and the way I have it connected. An answer would be nice and not a smart comment.
Last edited by ddunmore81; April 16th, 2018 at 07:57 AM.
What zeeke was saying is there are 2 types of V8 valves, and they work opposite one w vacuum one w out vacuum. IDK if the 6 uses the same valves but it's possible you have the wrong valve for the application, to rule that out try it w a known vacuum source applied and w no vacuum applied to see if it shuts off the heat in one configuration
What zeeke was saying is there are 2 types of V8 valves, and they work opposite one w vacuum one w out vacuum. IDK if the 6 uses the same valves but it's possible you have the wrong valve for the application, to rule that out try it w a known vacuum source applied and w no vacuum applied to see if it shuts off the heat in one configuration
All 1972-earlier Cutlii use a valve that is normally closed and opens with vacuum applied. ALl 1973-up use a valve that is normally open and closes with vacuum applied. Like motor mounts and water pumps, most vendors have the wrong parts listed.
What zeeke was saying is there are 2 types of V8 valves, and they work opposite one w vacuum one w out vacuum. IDK if the 6 uses the same valves but it's possible you have the wrong valve for the application, to rule that out try it w a known vacuum source applied and w no vacuum applied to see if it shuts off the heat in one configuration
What valve are we talking about? Also what is L-6 in the picture below? I don't have anything connected to that on the Heater Valve Vacuum Switch
All 1972-earlier Cutlii use a valve that is normally closed and opens with vacuum applied. ALl 1973-up use a valve that is normally open and closes with vacuum applied. Like motor mounts and water pumps, most vendors have the wrong parts listed.
Joe, I think the change over year for the heater valve on A-bodies was '71. The threaded port where the heater valve screws into the intake is smaller on a '70; the '71-'72 is larger. I ran into this problem with my '71 Cutlass when I swapped the 2-barrel intake for a '70 4-barrel intake. I couldn't get the AC to work properly until I installed a '71 4-barrel intake and reinstalled the '71 heater valve.
Joe, I think the change over year for the heater valve on A-bodies was '71. The threaded port where the heater valve screws into the intake is smaller on a '70; the '71-'72 is larger. I ran into this problem with my '71 Cutlass when I swapped the 2-barrel intake for a '70 4-barrel intake. I couldn't get the AC to work properly until I installed a '71 4-barrel intake and reinstalled the '71 heater valve.
Olds changed to larger ports throughout the cooling system in 1971 (radiator, water pump inlet, and the port on the intake for the heater valve) to account for hotter running engines due to emissions requirements. The function of the heater valve changed on the full size cars in 1971 since the HVAC system completely changed with the body style change. The A-body cars did not change heater valve function until the body style change in the 1973 model year.
This diagram is from the A-body A/C chapter of the 1972 CSM. Note that the water valve is connected to port 3 on the smaller vacuum switch. Note also the lower note under the table that says "Temperature lever valve connects ports 1 and 3 when lever is moved from cool to warm." Port 1 is manifold vacuum, so full vacuum is applied to the water valve when the temp lever is in WARM. That means it is normally closed and opens when vacuum is applied.
This page, also from that chapter of the 1972 CSM, spells it out in no uncertain terms in the second paragraph under Heat (Fig. 1C-2).
Olds changed to larger ports throughout the cooling system in 1971 (radiator, water pump inlet, and the port on the intake for the heater valve) to account for hotter running engines due to emissions requirements.
That's not quite right. The water pump inlet and radiator outlet nipples got SMALLER in 1971. In 1970 and earlier, the water pump inlet was 2" and the radiator outlet was 1.75", then in 1971 the water pump inlet decreased to 1.75" and the radiator outlet decreased to 1.5".
I have the same valve on the shelf for my car.
It is stamped with:
TYPE H25
RANCO
COLO, USA
The backside has an ink label:
H25-124
The valve is normally open and takes vacuum to close.
Just today I was working on the car, changing the heater core and I'll install the new heater valve tomorrow. I connected a vacuum gauge to the heater valve vacuum hose on my car and it has no vacuum with the temp slider on WARM and vacuum with the temp slider on COOL, so this valve matches my car's vacuum operation.
I recommend you check the vacuum operation on your '72 to ensure it matches your heater valve as my '71 operates opposite of what the factory manual describes per Joe's posts.
Thanks guys this all the info I need I have more than enough to go troubleshoot now. Also I meant to type 350 must of fat fingered it. I think i connected the heater control vacuum hoses to 2 & 3. I'll keep you posted
Olds changed to larger ports throughout the cooling system in 1971 (radiator, water pump inlet, and the port on the intake for the heater valve) to account for hotter running engines due to emissions requirements. The function of the heater valve changed on the full size cars in 1971 since the HVAC system completely changed with the body style change. The A-body cars did not change heater valve function until the body style change in the 1973 model year.
Joe:
I wonder why I had the problems I did with the '70 heater valve in a '71 Cutlass? I assumed the '70 heater valve was the culprit as the threaded port was smaller than the '71 part. Care to hazard a guess why I had this experience? Thanks!
Ok guys I did some troubleshooting today after work and found out that all of the vacuum lines are all in the correct place. I also made sure they are working by sucking on them with the air on As I don’t have a vacuum pump to test them. That worked just fine though. Haha. What I did find is this piece in the picture is acting as a plug. When I had the motor rebuilt we didn’t know what it was for but it was plugged in so we plug it back in. My question is what supposed to be here or should I just drill a hole through it? Because this is blocking the vacuum from entering Vacuum reserve tank.
Last edited by ddunmore81; April 18th, 2018 at 07:09 PM.
I've never seen anything like that before. Why not remove it and connect the lines to each other? Where does it go to? If you follow the diagram you should have a vacuum line coming from the manifold to the reservoir then to the control panel and then to the heater control valve.
It appears to be an adapter to fit the pieces together. I tried to put a straight thru connector but it was too small to fit where the bigger hose is. If you look at the picture you can see the ends are different sizes. I had an assortment pack but couldn't fine what I needed in it. I'll go to the auto part store and see what I could fine. If anyone has an olds 350 I would love to see what connects to the manifold > vacuum reserve. The fact that air isn't flowing thru tells me that this is the issue.
April 15th, 2018, 09:43 PM
