Curiosity and Hypothetical: Two AC related questions

[Crunch]

1. What's the difference between running the defrost on cold and using the AC?



2. Since people frequently complain about the efficiency of post-freon AC systems, what would be needed to get a vehicle AC to work like a freezer and use it to super-cool the interior like a meat locker?

 

[HHhuntitall]

1. No difference, except air flow direction.



2. Post-freon? Please explain a little more... .

 

[Crunch]

1. No difference, except air flow direction.

That's what I thought, except the AC light doesn't come on when the defrost is used. In the past I thought about using it that way to direct the air flow up the windshield and along the roof line to get it to the back

2. Post-freon? Please explain a little more... .

R-134a doesn't seem to work as well as the old freon. I was wondering if the refrigerant used in freezers might work better, or if it was an insulation problem in the walls of the vehicle that would prevent the temp from getting down to freezing on the interior, or something in the design/architecture of the system that prevents it.



As an aside, I've always been fascinated with the working of air conditioners, and for years have wondered why a home AC system can't use a natural gas burner or a solar reflector to heat and move the refrigerant through the system. To me it seems that if a byproduct of compression is heat, why couldn't the processed by reversed and use heat be used to pressurize the refrigerant, displacing it in such a way that it moves through a series of one-way valves until it hits the expansion valve? It seems that would drastically cut the amount of electricity needed to run the system (since the compressor is the biggest energy hog), leaving the fan as the only real electrical cost.

 

[Motorhead]

Using the A/C while the Defrost is on helps to de-humidify the cab. The moist heated air gets pulled past the cold A/C evaporator and the moisture collects on it.

I have used Dura cool in R12 systems. It can also be used in R134 systems. It gets a lot colder than R134.

 

[HHhuntitall]

I've used several types of refrigants in automotive, especially the older trucks now that R-12 is not so easily available. R-22, the older type of freon used for almost a century in home appliances, is becoming harder to find as well. It and R-12 were designed to be used with an expansion valve type system, where gasses are restricted by temperature of a probe inserted in the evaporator coils. An orifice is used with R-134, which lets the compressor run more, allowing it to wear faster, build more heat, and the dealer to sell more parts, and Dupont to make more R-134 since their patent has run out on R-12... ... oh, wait, that would make logical sense... . how about R-134 is more safe for the environment? Whatever. I've not used DuraCool, or know what it's chemical composition is. The biggest problem with reverse flow heat systems, is the lack of need. They are readily used in residential air, but in automotive, why heat the passenger compartment with freon, when you have hot engine coolant so readily available, and you don't have to turn a compressor to get it? As for it running on the defrost mode, I don't like that, as there are often times when I don't need it. If I wanted the compressor on, I'd switch it on, but then, I'm too stupid to know when I REALLY need it, so some engineer decided to do it for me..... and remind to take my key out of the ignition and turn off my lights, too... ... .



As for a solar heater, I doubt enough energy can be developed to pump refrigant at a high enough capacity to make it feasible. It takes a lot of energy to build enough head pressure to liquify the freon, then pass it through a cooler to a small orifice, allowing it vaporize, absorbing energy and cooling the air passed over it.



In residential use, reverse heating with freon is called Heat-Pump by Trane..... ever see an outside unit frozen into a solid block of ice in the winter? That's a heat-pump. They really don't generate enough heat unless you live in a really mild climate.

 

[rscurtis]

Dura Cool is a blend of refrigerants, one of them being 134. As it leaks, the different components of it leak at different rates, so it can not be simply topped up, it must be evacuated and recharged.



IMO, R12 is a better refrigerant than any that have followed it. I have a good supply of it for the old Mercedes. 134 doens't work that well in it, as it doesn't have enough condensing capacity. I would be tempted to use it in the Dodge when it becomes necessary to take advantage of its propensity to leak less and its lower head pressure which is easier on the compressor.



HH, R12 with work with a TX valve or an orifice system. GM used it for years in their CCOT system.

 

[Bill Stockard]

R-134a doesn't seem to work as well as the old freon. I was wondering if the refrigerant used in freezers might work better, or if it was an insulation problem in the walls of the vehicle that would prevent the temp from getting down to freezing on the interior, or something in the design/architecture of the system that prevents it. .

I think it has more to do with the design of the HVAC system than whether it uses R-12 or R-13A. My wife's Honda Odyssey with dual air system (R134A)will make it cold enough inside to "hang meat" on a 100 degree day.

As an aside, I've always been fascinated with the working of air conditioners, and for years have wondered why a home AC system can't use a natural gas burner or a solar reflector to heat and move the refrigerant through the system...

It has been tried. It's called an absorption system. Some local natural gas utilities sold them to a few homeowners in the late 60s. They were "slower than the Christmas itch" on the cooling cycle and were eventually replaced with electric compressor type systems. The absorption type systems are commonly found in RV refrigerators which are slow to cool and must be kept very close to level.

To me it seems that if a byproduct of compression is heat, why couldn't the processed by reversed and use heat be used to pressurize the refrigerant, displacing it in such a way that it moves through a series of one-way valves until it hits the expansion valve? It seems that would drastically cut the amount of electricity needed to run the system (since the compressor is the biggest energy hog), leaving the fan as the only real electrical cost.

The heat coming out of the condenser is heat that was removed by the evaporator. The compressor is the "pump" that moves the refrigerant through the system. Without the compressor, it won't work.



Bill

 

[HHhuntitall]

Dura Cool is a blend of refrigerants, one of them being 134. As it leaks, the different components of it leak at different rates, so it can not be simply topped up, it must be evacuated and recharged.



IMO, R12 is a better refrigerant than any that have followed it. I have a good supply of it for the old Mercedes. 134 doens't work that well in it, as it doesn't have enough condensing capacity. I would be tempted to use it in the Dodge when it becomes necessary to take advantage of its propensity to leak less and its lower head pressure which is easier on the compressor.



HH, R12 with work with a TX valve or an orifice system. GM used it for years in their CCOT system.

I'm gonna have to agree with you. R12 works so much better. I've converted several of my tractors to R134, and some of the trucks I've had in the past. I've never been happy with the conversion, but some cooling is better none at all!! Especially when you're sitting behind a fully loaded, 360hp 855 Cummins, moving 5. 5mph with the wind in a dusty cloud... . But I've also had a great deal of success with Freeze 12 in my ag equiment. Is that similar to AirGas's FR12 in the above link?



As for the 134 conversions, the Dodge's tend to work better, as they always seem to have bigger condensors. The old Chevy's I've had never worked worth a poo unless you put a big electric fan in front of it. Partly, the expansion valve is to blame, I think, as I made a line with an expansion orifice from a '95 and installed on my '91, and it worked a lot better than previously. Perhaps the expansion valve didn't close off enough? I don't know. I've never tried it, but I often wondered if R12 would work with an orifice. I've got a VERY limited supply, but I keep that to top off the '93 and my old Case 2390, if, or more like, when they need it.



Anyone have any experience with the FR12 from AirGas? And what's the cost? Is it available in cans or only in poundage bottles?

 

[Bill Stockard]

Especially when you're sitting behind a fully loaded, 360hp 855 Cummins, moving 5. 5mph with the wind in a dusty cloud?

It sounds like you are inside the cab of a Steiger. My brother has one and it's still on R-12... nice and cool in a dust cloud pulling a 35' chisel plow through wheat stubble on a 100 degree day. When I moved my shop 5 years ago, I gave him all my hoarded R-12 since I don't own anything using R-12 any more.



Bill

 

[HHhuntitall]

It sounds like you are inside the cab of a Steiger. My brother has one and it's still on R-12... nice and cool in a dust cloud pulling a 35' chisel plow through wheat stubble on a 100 degree day. When I moved my shop 5 years ago, I gave him all my hoarded R-12 since I don't own anything using R-12 any more.



Bill

Close, but I prefer a little bigger transmission, that's not married to the back of the motor... . it's a Versatile! You only have to pull the driveshaft to work on the clutch or transmission, not drop it off the back of the motor and take the cab off to do it..... and there's no tranfer case. The front driveshaft is driven off an output spline on the front of the transmission, same as the rear shaft. Everything but the tires and interior can be found at Inland or TruckPro...



But it does work much better on R-12 or Freeze 12!! It will be going back the next time I have to replace the compressor!!

 

[Bill Stockard]

Close, but I prefer a little bigger transmission, that's not married to the back of the motor... . it's a Versatile! You only have to pull the driveshaft to work on the clutch or transmission, not drop it off the back of the motor and take the cab off to do it..... and there's no tranfer case. The front driveshaft is driven off an output spline on the front of the transmission, same as the rear shaft. Everything but the tires and interior can be found at Inland or TruckPro...



But it does work much better on R-12 or Freeze 12!! It will be going back the next time I have to replace the compressor!!

Yep, my brother had the clutch replaced once and it was a bear. He has had a few problems with the planetaries at the ends of the axles. It has done a lot of heavy work for many years and the big Cummins keeps on roaring.



Bill

 

[BGlidewell]

1. No difference, except air flow direction.

.

it locks out recirculation too.

 

[Crunch]

I think it has more to do with the design of the HVAC system than whether it uses R-12 or R-13A. My wife's Honda Odyssey with dual air system (R134A)will make it cold enough inside to "hang meat" on a 100 degree day.

I was thinking it was probably a design issue. On the smaller vehicles I can see how a larger condenser and compressor would be a drag on the engine, but the 5. 9 Cummins doesn't seem to notice the AC is even there, and I don't notice any effect on fuel economy when running the AC. I think they could put a larger system on these trucks without any negative effect.

It has been tried. It's called an absorption system. Some local natural gas utilities sold them to a few homeowners in the late 60s. They were "slower than the Christmas itch" on the cooling cycle and were eventually replaced with electric compressor type systems. The absorption type systems are commonly found in RV refrigerators which are slow to cool and must be kept very close to level.

Was the problem that they couldn't move the refrigerant fast enough as compared to a compressor? I also thought that RV refrigerators, at least in the old ones, used ammonia as the refrigerant.

The heat coming out of the condenser is heat that was removed by the evaporator. The compressor is the "pump" that moves the refrigerant through the system. Without the compressor, it won't work.

Isn't heat the byproduct of compressing anything? I'd always heard the refrigerant heats up as it gets compressed.

 

[HHhuntitall]

it locks out recirculation too.

... as in it only pulls in fresh air?