AC blows out defrost
Pro
Joined: Mar 2006
Posts: 700
Likes: 2
From: Spring Hill Florida
Fitting
Under the hood, right behind the distributor is a vacuum fitting where two or three line meet. One of those lines goes to that "pot" if the pot is OK one of the lines is bad or just loose.
Le Mans Master
Joined: Feb 2005
Posts: 6,486
Likes: 566
From: Clearwater Florida
….. That same vacuum source also operates the cruise control dashpot … I'm not sure how the '84 is set-up for cruise , but on my '87 the hose from the firewall out to the cruise pot had disintegrated most likely from brake fluid as it is routed under the M/C …..
Burning Brakes
Joined: Nov 2004
Posts: 1,193
Likes: 176
From: Hillsborough NC
You didn't specify if you had the C68 automatic climate control in your vette, and I am not sure if it was even an option in 84 (don't think it was). My answer below will apply to the manual climate control system (the one with sliders for temperature and system function).
When the system loses vacuum, the actuator default positions are for heat and defrost (a consequence of our cars being designed in Detroit I guess
).
If you check your lines and they are OK, I would suggest looking at the rotary switch on the back of the panel that directs the vacuum. These switches are constructed of two plates that have a maze of passages cut into them. As you move the slider, the back plate rotates and directs vacuum to the appropriate actuators, which redirects the airflow as appropriate. The seal between these two plates is a high viscosity grease that will deteriorate with age. The seal works because the grease is too thick for the vacuum to suck it from the plates into the system, but it does dry over many years. If you do a search on the forum you will find many posts relating to this usually followed by complaints that the replacements available at vendors are hit and miss and don't work well.
I would not recommend buying a replacement.
The two plates can be disassembled, cleaned and you can apply a fresh coat of the grease to the raised edges on the plates. Once you re-assemble the two plates, put a small coating of grease around the outer edge to seal it. Be careful with how much grease you use because if you use too much, you can impede or block the passages with the grease. This will make itself evident with slow response from the actuators (partial block), or not changing the air flow at all if the passage is completely blocked.
The grease is available at Amazon and other vendors and is about $13. Link Below:
Of course, if your hoses are shot, you will need to fix them as well, but if your hoses check out and you have the manual controls, I would suggest looking here next.
Worked like a champ on mine (86).
Good Luck
When the system loses vacuum, the actuator default positions are for heat and defrost (a consequence of our cars being designed in Detroit I guess
).If you check your lines and they are OK, I would suggest looking at the rotary switch on the back of the panel that directs the vacuum. These switches are constructed of two plates that have a maze of passages cut into them. As you move the slider, the back plate rotates and directs vacuum to the appropriate actuators, which redirects the airflow as appropriate. The seal between these two plates is a high viscosity grease that will deteriorate with age. The seal works because the grease is too thick for the vacuum to suck it from the plates into the system, but it does dry over many years. If you do a search on the forum you will find many posts relating to this usually followed by complaints that the replacements available at vendors are hit and miss and don't work well.
I would not recommend buying a replacement.
The two plates can be disassembled, cleaned and you can apply a fresh coat of the grease to the raised edges on the plates. Once you re-assemble the two plates, put a small coating of grease around the outer edge to seal it. Be careful with how much grease you use because if you use too much, you can impede or block the passages with the grease. This will make itself evident with slow response from the actuators (partial block), or not changing the air flow at all if the passage is completely blocked.
The grease is available at Amazon and other vendors and is about $13. Link Below:
Of course, if your hoses are shot, you will need to fix them as well, but if your hoses check out and you have the manual controls, I would suggest looking here next.
Worked like a champ on mine (86).
Good Luck
