Gear ration affect a/c compressor?

[MassDart]

I was having a conversation with a fellow Mopar guy at a recent Cruise night and mentioning that I wanted to change my 8 3/4 rear to 3.55:1 next spring. He mentioned that I might need to be careful as it could over speed the a/c compressor (original Mopar compressor) and damage it. Is that true? I've heard that there are issues regarding alternator speed (not sure if that's really a case either) Car is a 1967 Dart with a mild-ish 360 Magnum. Current rear gears are 2.94. 904 Auto. Using a calculator, my effective gear ration currently with 205 60 14 tires, is 3:1. Looks like putting in 3.55 gears with those tires would result in 3.64:1. Has anyone had issues with their a/c compressors changing gears?

I wasn't sure if this is the right place for this question, but thought I'd start here.

Thanks!

Doug

 

[FlamesAreWicked]

I would say no…. 3.55 isn’t all that aggressive of a gear.. plus there’s been plenty of factory equipped AC cars with 4.10s even. I personally wouldn’t be concerned about it since there’s 10s of thousands of cars out there with a 3.55 or numerically higher gears out there’s with A/C

 

[AJ/FormS]

plus
How high are you gunna rev it, lol.

 

[MassDart]

I would say no…. 3.55 isn’t all that aggressive of a gear.. plus there’s been plenty of factory equipped AC cars with 4.10s even. I personally wouldn’t be concerned about it since there’s 10s of thousands of cars out there with a 3.55 or numerically higher gears out there’s with A/C

Pretty much what I thought. Much appreciated.

 

[MassDart]

Olus
How high are you gunna rev it, lol.

Well, my cams sweet spot is 1500-5200, so I typically don't usually go harder than 6000 ish.

 

[AJ/FormS]

(6000 x 85") / (1056 x 3.55) =136mph in top gear, at no slip. Then;
(136/2.45) x .93slip= 52mph in first gear@6000
(136/1.45) x .93slip= 87 mph in second @ 6000
65 in Second will be ~ 4150.

>85 is a 27" tire. Your tires are only 74.4, but I'll wager those 205s are gonna be toasted pretty quick ....... else why bother with a "mildish 5.9M"?
>1056 is a correction factor to turn it all into mph.
>.93 is expected slip in the convertor at WOT.
>A727 Torquefllite gears are 2.45-1.45-1.00

 

[lemondana]

In the mid 70's, ma mopar put hi speed cutout switches in the power wire for the compressor on the cop cars. They screwed on the high side fitting and just plugged in the big power wire. So if would cut power if too high rpm and pressure. I can find the part number tomorrow, they are on Ebay once in a while.

 

[RustyRatRod]

No. Complete bs. Sounds some idiocy a Chevy guy would say.

 

[Charrlie_S]

In the mid 70's, ma mopar put hi speed cutout switches in the power wire for the compressor on the cop cars. They screwed on the high side fitting and just plugged in the big power wire. So if would cut power if too high rpm and pressure. I can find the part number tomorrow, they are on Ebay once in a while.

That is not totally correct. Those switches had noting to do with RPM. Would just shut off the compressor if the high side AC pressure was excessive (and/or too low due to system leak, depends on year/vehicle)

 

[MassDart]

(6000 x 85") / (1056 x 3.55) =136mph in top gear, at no slip. Then;
(136/2.45) x .93slip= 52mph in first gear@6000
(136/1.45) x .93slip= 87 mph in second @ 6000
65 in Second will be ~ 4150.

>85 is a 27" tire. Your tires are only 74.4, but I'll wager those 205s are gonna be toasted pretty quick ....... else why bother with a "mildish 5.9M"?
>1056 is a correction factor to turn it all into mph.
>.93 is expected slip in the convertor at WOT.
>A727 Torquefllite gears are 2.45-1.45-1.00

I was mistaken in my post. Tires are 215 60 14s, not that I think it makes much difference. The car basically boils tires at will. Thanks for the info!

 

[MassDart]

No. Complete bs. Sounds some idiocy a Chevy guy would say.

Its funny, while I was being told this an Olds guy was telling me stories of how his buddies with 442s were killing their compressors with gear changes.

 

[RustyRatRod]

Its funny, while I was being told this an Olds guy was telling me stories of how his buddies with 442s were killing their compressors with gear changes.

That's hilarious. I went to school with a guy who had a 68 442 stone stock. 400, 4 speed car with factory 3.73 gears. He used to see how long he could lay drag. He laid two streaks over 2/3 of a mile. Broken of course, where he shifted. lol His AC worked just fine. lol That was one of the quickest and fastest production cars I've ever been in. It was NICE too.

 

[Bodyperson]

The way I understand the AC system, it releases the clutch on the compressor at a specific pressure all of the time. RPM could be a contributing factor as to how often this accrues. A gear change should not affect its ability to do so.

 

[Charrlie_S]

The way I understand the AC system, it releases the clutch on the compressor at a specific pressure all of the time. RPM could be a contributing factor as to how often this accrues. A gear change should not affect its ability to do so.

Depending on year and model there could be 1 or 2 pressure switches, and/or a temp (thermostat) control. High pressure sw, on drier or fitting on high side line. Low pressure switch on drier, or at expansion valve on low side line. Thermo sw at low side line near firewall or in evaporater. The sw on the drier could be low pressure, or high pressure, or a binary sw, that will sense both high and/or low pressure. Certain models also had a WOT switch, which would turn off the compressor at wide open throttle.

 

[RustyRatRod]

Some of the systems also employed a pressure switch in the power steering system so that when the wheel was turned all the way one direction or the other and the P/S pressure spiked, it would release the AC clutch.

 

[lemondana]

That is not totally correct. Those switches had noting to do with RPM. Would just shut off the compressor if the high side AC pressure was excessive (and/or too low due to system leak, depends on year/vehicle)

Well-I've only seen them on police and Highway patrol cars. So you don't think when the patrolman kicks that fuck_in 440 down and runs it up to 130 that rpm doesn't have anything to do with it?

 

[lemondana]

That's hilarious. I went to school with a guy who had a 68 442 stone stock. 400, 4 speed car with factory 3.73 gears. He used to see how long he could lay drag. He laid two streaks over 2/3 of a mile. Broken of course, where he shifted. lol His AC worked just fine. lol That was one of the quickest and fastest production cars I've ever been in. It was NICE too.

One of my best friends also had a 68 442, 4 speed, AC, don't know what rear and a bigger cam, and an Edelbrock intake. He was tired one night coming home from a kegger and asked me if I wanted to drive-Sure. If I would have raced him, my 340 4 speed Dart would have eaten him alive. It was a really beautiful car and it handled really nice but I remember that he had wheelhop real bad. If someone gave me one, I would keep it.

 

[lemondana]

Well-I've only seen them on police and Highway patrol cars. So you don't think when the patrolman kicks that fuck_in 440 down and runs it up to 130 that rpm doesn't have anything to do with it?

The high pressure comes from extended high rpm I would think. Isn't that kind of the reason that AC wasn't available on the 440 with a 4 speed?

 

[RustyRatRod]

One of my best friends also had a 68 442, 4 speed, AC, don't know what rear and a bigger cam, and an Edelbrock intake. He was tired one night coming home from a kegger and asked me if I wanted to drive-Sure. If I would have raced him, my 340 4 speed Dart would have eaten him alive. It was a really beautiful car and it handled really nice but I remember that he had wheelhop real bad. If someone gave me one, I would keep it.

I'm sure that's accurate, too. A bodys are really light. Add in 340 and they're deadly! But we know that already! lol

 

[Charrlie_S]

Some of the systems also employed a pressure switch in the power steering system so that when the wheel was turned all the way one direction or the other and the P/S pressure spiked, it would release the AC clutch.

Off the top of my head, I don't remember that switch on Mopars of the vintage in question. I would have to check my manuals to refresh my memory. But that is correct for some AC systems.
Rob, do you remember any models specifically?

 

[RustyRatRod]

Off the top of my head, I don't remember that switch on Mopars of the vintage in question. I would have to check my manuals to refresh my memory. But that is correct for some AC systems.
Rob, do you remember any models specifically?

No, I was speakin generally. Like you, I've not seen it on Mopars, but GM used it prolifically. It wouldn't surprise me if it's not on a Mopar somewhere. I would look for it maybe on something with a smaller engine like the 2.2 and 2.5.

 

[lemondana]

I've seen them on 1975 Gran Fury 440 Nebraska State Patrol car, 1978 Omaha b body police car 360, and a 1988 Diplomat 318-4 Lincoln police car. The part number is 3503744. Listed as an A/C Hi Pressure Cut Out Switch.

 

[mbaird]

Didn’t police pkgs have adjustable voltage regulators ?

 

[Charrlie_S]

I've seen them on 1975 Gran Fury 440 Nebraska State Patrol car, 1978 Omaha b body police car 360, and a 1988 Diplomat 318-4 Lincoln police car. The part number is 3503744. Listed as an A/C Hi Pressure Cut Out Switch.

I can tell you right now, the 88 Diplomat does not have a power steering high pressure AC cutout switch. Got one of those in my yard right now. It has a refrigerant low pressure cutout switch mounted on the "H" valve.

 

[Charrlie_S]

I've seen them on 1975 Gran Fury 440 Nebraska State Patrol car, 1978 Omaha b body police car 360, and a 1988 Diplomat 318-4 Lincoln police car. The part number is 3503744. Listed as an A/C Hi Pressure Cut Out Switch.

That part number is for a High refrigerant pressure switch, not for a power steering high pressure sw.
This thread has come off the tracks.