TheBMan Posted July 13, 2021 Share Posted July 13, 2021 Working on my A/C, 1972 Monte Carlo. Has anyone ever replaced or repaired the vacuum actuator or blend door for the heater core? The one that closes off air flow over the heater core and into the duct work when the A/C is on. My A/C has excellent pressures (220 high, 30 low) but only blows 60~ degrees from the vents. The Recirculate blend doors both work as they should. We pinched off the heather hoses and the air from the vents dropped to 45 degrees so I suspect that door isn't closing as it should and is letting hot air pass over the heater core and mixing with the A/C air. Any suggestions, advice, or tips and how it's accessed or tips on known issues, etc? I'm always looking for solutions that don't have me reinventing the wheel. I figure that if I'm having the problem, someone else has probably had it before me. Thanks! Quote Link to comment Share on other sites More sharing options...
Leghome Posted July 13, 2021 Share Posted July 13, 2021 On my 72 we had to put a shut off valve in the heater hose in order for the AC to cool properly 1 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted July 13, 2021 Share Posted July 13, 2021 IDK why, but each year first gen has differences in the way the a/c works. The 70s and 71s have a heat control valve. The 70 is on the passenger fender well and the 71 has it in the intake manifold near the water pump. Both styles are in the heater hose going to the heater core to stop the flow of hot water. The 72 has no such valve. Other owners with a/c equipped 72s have also complained about the issue you have described. 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 13, 2021 Share Posted July 13, 2021 My '72 makes cold air coming from all the vents. When I had everything apart, I double checked to make sure all the actuators and blend doors worked and had full range of motion. I also replaced any foam seals I could with one of the rebuild kits out there. Wasn't the greatest kit and no instructions where the various seals went, but it seems good. Maybe it's possible it could be even colder if I pinched the heater hose off, but when I charged the system up, the measured temperatures coming out of the vents were really good. So, I think it's possible for a 72 to work good, but maybe I just got lucky that everything lined up properly? 1 Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 13, 2021 Share Posted July 13, 2021 Just a question. Forgive my stupidity. Lol. If the heat issue is prevalent to the 72’s than why can’t a 70 or 71 style heat valve be installed? 1 Quote Link to comment Share on other sites More sharing options...
Brew Posted July 13, 2021 Share Posted July 13, 2021 My 70 has one of these like MC1of80 described. Maybe replace or install one if you don’t got. it is vacuum controlled so your cabin air conditioning controller would have to have that line / function. Again, MC covered that. just thought you might need a picture 1 Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 13, 2021 Share Posted July 13, 2021 1 hour ago, Brew said: My 70 has one of these like MC1of80 described. Maybe replace or install one if you don’t got. it is vacuum controlled so your cabin air conditioning controller would have to have that line / function. Again, MC covered that. just thought you might need a picture Yep. Like this. Well done DB. I don’t know if the 72 has the hole (plugged) in the intake. But I think it does? Quote Link to comment Share on other sites More sharing options...
TheBMan Posted July 13, 2021 Author Share Posted July 13, 2021 2 hours ago, MC1of80 said: IDK why, but each year first gen has differences in the way the a/c works. The 70s and 71s have a heat control valve. The 70 is on the passenger fender well and the 71 has it in the intake manifold near the water pump. Both styles are in the heater hose going to the heater core to stop the flow of hot water. The 72 has no such valve. Other owners with a/c equipped 72s have also complained about the issue you have described. @MC1of80 This is great info. Adding the valve seems like a viable solution provided I have the right vacuum source. That said, I'd like to keep the car as original as possible so I'm going to keep investigating why air is getting past the heater core and mixing with the air going over the evaporator. I'm sure it has something to do with that blend door and vacuum actuator. Quote Link to comment Share on other sites More sharing options...
TheBMan Posted July 14, 2021 Author Share Posted July 14, 2021 21 hours ago, Brew said: My 70 has one of these like MC1of80 described. Maybe replace or install one if you don’t got. it is vacuum controlled so your cabin air conditioning controller would have to have that line / function. Again, MC covered that. just thought you might need a picture Hey @Brew, I think I'm going to go this route. I bought the valve that screws into the intake manifold rather than the one you pictured that attaches to the fender well. My question is this: where on your car does the vacuum line route and what does it connect to? According to the vacuum diagram I have for 70-71, the vacuum line connects to the heather control panel and I do have the [empty] port for it BUT I don't know where the line runs through the firewall and I can't find any clear photos to show me. Assuming yours passes through the firewall, can you tell me where or snap a photo and post it? I don't have any empty holes in my firewall and I don't want to drill hole(s) that aren't needed. Thanks! Quote Link to comment Share on other sites More sharing options...
Brew Posted July 14, 2021 Share Posted July 14, 2021 The heater box has a rubber grommet that takes the lines through the firewall. 1 Quote Link to comment Share on other sites More sharing options...
TheBMan Posted July 14, 2021 Author Share Posted July 14, 2021 @Drew Yes, I have the same hole (see attached image) BUT mine has a grommet with one line (not surprising). I'll have to see if I can find that grommet somewhere or retrofit something. Thank you very much for doing that! Very helpful! EDIT: I'm sure I can make this one work. I'll drill a hole through the grommet and push a piece of metal tubing for 5/32" vacuum line through it to connect the vacuum line on each side of the firewall and put it back in place. Should work very nicely. 1 Quote Link to comment Share on other sites More sharing options...
Brew Posted July 14, 2021 Share Posted July 14, 2021 👍🏼 1 Quote Link to comment Share on other sites More sharing options...
TheBMan Posted July 16, 2021 Author Share Posted July 16, 2021 Quick update on this. Pictures attached. I added the intake manifold mounted heater valve and tapped into the manifold vacuum port on the rear of the intake manifold. Vacuum holds the valve closed so I have vacuum to the valve any time the car is running. I decided that I didn't want to tap into the existing vacuum port on the heat/ac control panel in the dash because when the A/C isn't on, there will be no vacuum to the valve and it will allow hot water to flow through the heater core and defeat the purpose of the valve. Once the heater core is hot, there is no going back/cooling it off, at least not quickly. In the fall, when the weather cools, I'll cap the valve so I have heat and remove the vacuum line until spring. It's not the perfect solution because I want to keep the car original but the only way to address the A/C issue otherwise is to remove the heater box to access the vacuum diaphragm that controls the heat/ac blend door. Maybe that's a project for this winter. Thanks to everyone for the tips and suggestions! @Brew@jft69z@Dtret@MC1of80@Leghome 1 Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 16, 2021 Share Posted July 16, 2021 Glad you got it. Originality is all well and good but sometimes functionality and safety have to take president ( passenger side door mirror). Just a thought, next time you do something with the antifreeze change that heater hose it will make the valve look like it belongs there. Very nice looking engine. Well done Quote Link to comment Share on other sites More sharing options...
TheBMan Posted July 16, 2021 Author Share Posted July 16, 2021 21 minutes ago, Dtret said: Glad you got it. Originality is all well and good but sometimes functionality and safety have to take president ( passenger side door mirror). Just a thought, next time you do something with the antifreeze change that heater hose it will make the valve look like it belongs there. Very nice looking engine. Well done @Dtret, are you referring to the orange heater hose? And thanks, I agree that functionality and safety are more important. Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 16, 2021 Share Posted July 16, 2021 1 hour ago, TheBMan said: @Dtret, are you referring to the orange heater hose? And thanks, I agree that functionality and safety are more important. Yes but I’m not doing it in a mean way. I know that you are after originality. 1 Quote Link to comment Share on other sites More sharing options...
TheBMan Posted July 16, 2021 Author Share Posted July 16, 2021 25 minutes ago, Dtret said: Yes but I’m not doing it in a mean way. I know that you are after originality. @Dtret No worries, I didn't take it as being mean! I just wanted to be sure I knew what you were referring to. I wasn't sure if the orange hose was original-style. Thanks for confirming! Quote Link to comment Share on other sites More sharing options...
TheBMan Posted July 19, 2021 Author Share Posted July 19, 2021 On 7/16/2021 at 11:43 AM, Dtret said: Yes but I’m not doing it in a mean way. I know that you are after originality. Hey @Dtret, I thought you'd like to see this. Thanks for the nudge. Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 19, 2021 Share Posted July 19, 2021 53 minutes ago, TheBMan said: Hey @Dtret, I thought you'd like to see this. Thanks for the nudge. You know it looks better and the new valve looks like it’s supposed to be there. Well done. 1 Quote Link to comment Share on other sites More sharing options...
Brew Posted July 19, 2021 Share Posted July 19, 2021 That looks great! Good job! 👍🏼👍🏼 Quote Link to comment Share on other sites More sharing options...
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