A/C heater control

[Martin1313]

Does anyone know if 1974 a/cheater controls will work in a 73?

 

[Charlie]

 

[75gmck25]

Based on the LMC catalog, replacement '73 controls are different than '74, but its hard to tell what changed.

I'm using controls from a late '70's truck in my '75, and the key point is that you need to have the soft rubber plug/adapter that connects to the back of the controls. GM never changed the number of vacuum doors over the years, but the vacuum ports on the back of the controls did change a little. That rubber adapter is what you use to connect the right port to the right vacuum actuator.

Just to give you an idea of the type of changes over the years- My '75 controls (same as '74) have a bi-level position, which means you get heat and defrost (compressor is also on). The newer controls have a high-low position, which means heat and dash vents (no compressor). I thought the high-low position might make more sense for the most economical driving, and it works fine after I swapped controls.

If you download the manual pages for the '74 and '73 controls you can see what actuator is connected to each port on the back of the switch, and then just match them up. You may also have to make some minor mods to the electrical connection, since in '74 when the controls were set to max A/C it also kicked the blower on high. I don't know if the '73 used the same setup.


Bruce

 

[Martin1313]

Thanks for the information, that should help me out. I can’t shut the heat off. I live in SE TX and it’s cooking me.

 

[Preston]

Welcome to GMSB from Virginia
May need to change heater control valve and or cable
Good luck

 

[75gmck25]

If you can't move the heater temp slider to full cold, its probably the blend door or the cable. On most square body trucks the heater always has water circulating through it, and there is no heater control valve to shut water off. Control of heat is through the blend door, which sends air through the heater core or through the A/C evaporator. The downside of this arrangement is that the heater plenum never really gets cool because the heater core and evaporator are very close to each other.

If you take off the glove compartment door you can see a removable panel in the plastic heater plenum behind it. You can also see the top of the plenum where the blend door cable connects (just push the firewall insulation up and out of the way). Take the screws out and remove that plastic panel and you will see the blend door behind it. Now you can use the dash temp control to move the door back and forth and pull out all the junk that has fallen into the plenum. Once you get it cleaned out, then adjust the cable and make sure it fully closes when you push it to the cold position. It won't fix the heat problem entirely, but it will help a lot.

You can also try adding a heater shutoff valve in one heater hose, but when I tried this (I used to live in San Antonio and had to deal with the heat) it did not seem to make that much difference. It seemed like the plenum was still exposed to hot water, even though it was not flowing through it.

Bruce

 

[dvdswan]

Welcome to the site.

 

[Billy]

75Gmck25 has your answer. Please post what you find. I lost some money in there