How Does A/C work on a Carb vehicle?

[redhat]

When vehicles were carbureted, what adjusted idle speed for the A/C compressor surge?

Was there a device on the carb that would slightly open the throttle?

Also, I am assuming that without a engine computer managing anything, the A/C system at that point would rely solely on pressure sensors to engage its clutch to compress?

I'm guessing from inside the vehicle, when turning on the A/C, you'd be (A) sending power to your low speed fan relay to turn on the engine cooling fans/ or engaging the clutch fan, (B) be turning on some sort of idle controlling solenoid on the carb and (C) sending power to the A/C clutch circuit (with a pressure sensor inline?)...

 

[Malo83]

AC solenoid valve activated when you turn on AC, bumps up rpm.

 

[redhat]

AC solenoid valve activated when you turn on AC, bumps up rpm.

Thank you!

 

[hrv]

or nothing...

 

[dishdude]

I think some had a WOT switch that would disengage the compressor at full throttle so it wouldn't zap power from the engine. I've never owned or worked on a carbureted car so take that for what it's worth.

 

[brianl703]

I vaguely recall that at least one electronic feedback carburetor had an idle speed control just like you'd find on a fuel injected engine.

At that point you might as well just ditch the carburetor entirely and replace the mixture control solenoid with a throttle body injector.

 

[SeaJay]

I do remember some vehicles with A/C from the 70's and early 80's. The A/C worked great when it was no more than 85 degrees or so. But when it exceeded over 90 and there was stop and go traffic, engine temp overheating was what occurred.

 

[michaelluscher]

Idle up/high idle solenoid
When 12v is applied, it pushes on the throttle linkage
Illustrated in green on a E4ME Quadrajet

 

[billt460]

I loved the thimble sized fuel filters those old Quadrajet carburetors had.

 

[atikovi]

Idle up/high idle solenoid
When 12v is applied, it pushes on the throttle linkage
Illustrated in green on a E4ME Quadrajet
View attachment 141917

I don't remember seeing torx screws holding a carb together.

 

[billt460]

I don't remember seeing torx screws holding a carb together.

The newer ones that are rebuilt have them. It took them a long time to get away from Phillips head screws

T4-478 OEM

 

[Electromotive]

When vehicles were carbureted, what adjusted idle speed for the A/C compressor surge?

Was there a device on the carb that would slightly open the throttle?

Also, I am assuming that without a engine computer managing anything, the A/C system at that point would rely solely on pressure sensors to engage its clutch to compress?

I'm guessing from inside the vehicle, when turning on the A/C, you'd be (A) sending power to your low speed fan relay to turn on the engine cooling fans/ or engaging the clutch fan, (B) be turning on some sort of idle controlling solenoid on the carb and (C) sending power to the A/C clutch circuit (with a pressure sensor inline?)...

My 1985 Corolla Sedan with the 4AC engine and auto. trans. had some sort of vacuum/solenoid device on the carb. that would increase engine RPM when the A/C was turned on. This car had a very substantial and intricate metal vacuum piping plenum in the engine valve cover area with attached rubber vacuum hoses galore to control/regulate various parameters.

 

[Chris142]

As mentioned there was a solenoid that would raise the idle a little to compensate for the draw from the compressor running. As for how well they worked? Nothing worked better than gm's poa ac system with r12 in it and that 50 lb a6 compressor! Those would freeze a polar bear.

 

[walterjay]

I had an 80 something Cadillac that would freeze a popsickle.

 

[Mazomopar]

Seems like most of my "fleet" required putting it in neutral and giving it a little gas at a red light...higher rpm for the coldpressor and pull a little more air across the rad. The "good" old days.

 

[Astro14]

I do remember some vehicles with A/C from the 70's and early 80's. The A/C worked great when it was no more than 85 degrees or so. But when it exceeded over 90 and there was stop and go traffic, engine temp overheating was what occurred.

My ‘77 Oldsmobile was an icebox in any weather. 100 degrees, humid, idling in NYC traffic, it would still freeze you. The engine never overheated.

When cars like that (a luxury car, not a cheapie) were new, and when they were maintained, they worked great.

Most people’s experience with cars that had carburetors and AC are with 20+ year old heaps. Worn out fan clutches, poorly maintained cooling systems, undercharged AC, etc. That’s what I’m seeing here.

Not a fair assessment. That’s not how they were when new.

 

[dnewton3]

Way back in the day, when large discplacement Ford, GM and Mopar engines made prodigious torque, it was probably a moot point.

As engines got smaller and less powerful, there were small electronic solenoids that lightly bumped up the idle. When the A/C clutch came on, so did the carb balance solenoid.

 

[TheLastWord]

As mentioned there was a solenoid that would raise the idle a little to compensate for the draw from the compressor running. As for how well they worked? Nothing worked better than gm's poa ac system with r12 in it and that 50 lb a6 compressor! Those would freeze a polar bear.

This is so right. Those A6 GM units (Frigidaire?) with R12 and POA (Pilot operated absolute) were fantastic. Those large 4 core Harrison radiators (copper?) helped keep it cool.

I still have a 87 Accord with R12 in it and working great. Haven't recharged it for at least 20 years. Don't drive it much but still......

I forgot the model #'s but Ford and Mopar also had great systems also back in the day.

 

[billt460]

My 1991 F-150 was the last year Ford ran R-12. In 92 they went to R-134. I'm still running the original compressor. (32 years later).

It hasn't had any additional R-12 added in at least 15 years. And it will still freeze the balls off a brass monkey, here in the middle of the Mohave in the dead of Summer.

Granted it has the early Ford EFI, and no carburator. And all I have done to the fuel system is change the fuel filter. But as far as the A/C, I certainly have no room to complain.

 

[brianl703]

My 1991 F-150 was the last year Ford ran R-12. In 92 they went to R-134. I'm still running the original compressor. (32 years later).

It hasn't had any additional R-12 added in at least 15 years.

Ford switched over to barrier hoses sometime in the late 80s. Barrier hoses go a long way towards stopping R12 (and R134a) leakage.