Air Condition

[philip]

When you where driving, was it hot out? Was the a/c running?

Needles, CA in late August? Hot? A few weeks ago in Needles, you could add another EIGHT degrees.



When you've got A/C, by jingles you're running it on MAX.

[redmondjp]

Philip--those two pictures weren't taken at the same time, were they?

I have been doing my own A/C work (R12 systems only) for the last 20 years, and I've never been able to get more than about a 40 deg. F differential between ambient outside temp. and interior air duct temp.--maybe 35 degrees on a weak system, and 45 degrees on a good one. This is when using outside air into the evaporator and not in recirculation mode.

You've got some kicka$$ system if you can pull a 68 deg. differential! Is this in recirculate mode? You running some kind of magic freon you got from south of the border from the back of some guy's van along the side of the road?

[kassim503]

WOWWWW!!!!

That is a really good system!

That meakes long island seem cold! Actually its cold here now averaging on 70 degrees

[philip]

Philip--those two pictures weren't taken at the same time, were they?

Between the Colorado River and Needles, west I-40.

I have been doing my own A/C work (R12 systems only) for the last 20 years, and I've never been able to get more than about a 40 deg. F differential between ambient outside temp. and interior air duct temp.--maybe 35 degrees on a weak system, and 45 degrees on a good one. This is when using outside air into the evaporator and not in recirculation mode.

You've got some kicka$$ system if you can pull a 68 deg. differential! Is this in recirculate mode? You running some kind of magic freon you got from south of the border from the back of some guy's van along the side of the road?

Yes, I was using RECIRCULATED air. On FRESH air, the duct temperature was close to 10 degrees higher under these conditions. I tried it.

Not long after I got this truck, the compressor puked and with that repair came a long list of other replacements.

1 ) Brand new compressor
2 ) Heliarc repaired two chaffed metal pressure lines
3 ) Replaced every 0-ring on every coupling
4 ) New condensor
5 ) New rcvr/dryer
6 ) Wrapped all metal low pressure lines with 1" thick hot water pipe insulation.
7 ) Repaired air diverter door seal
8 ) Double checked hot water heater control valve operation
9 ) Made sure the total oil amount in the system was correct ... by the book
10 ) After evacuating the system, FOLLOW the charging procedure in the FSM to the letter. It may not be the process you've been using. In large part, the system is refilled through the high side with the system not running.
11 ) Use genuine Freon R-12 refridgerant. None of that Freeze12 dung or R-134a. The condensor is just too small for that stuff to work in this system when ambients are this high.

Then in fairness I should add that ambient humidity plays a huge roll in duct temperature. More humidity will raise duct temperature. You'll note the humity was "Lo" meaning, under 10% relative.

I have my own evac pump and gauges.

[kassim503]

11 ) Use genuine Freon R-12 refridgerant. None of that Freeze12 dung or R-134a. The condensor is just too small for that stuff to work in this system when ambients are this high.

Hes using the good stuff- I noticed warmer a/c temp ducts on every vehicle that I converted to r-134a. Ok fine it was only the maxima and a chevy 1500 p/u. Didnt do them for fun, the old refigerant leaked out, I would never want to downgrade my a/c, even if it made the ozone smile.

Too bad R-12 is hard to get, you need a liscence to get it. Too bad

[philip]

SNIP
Too bad R-12 is hard to get, you need a liscence to get it. Too bad

Let me say R-12 is not hard to get nor is a license required.

Ask my how "off-list."

R-134a and the "Freeze12" 60/40 mix products (R-12/R-134a) refrigerants do not absorb / release as much heat per time exposure as R-12. For this reason, the compensation with R-134a use is to enlarge both condenser and evaporator ... particularly the condenser. Since I traverse the deserts often enough, I too won't give up cooling when ambient temps soar past 100 degrees.

[kassim503]

Well, you're right about the r-12, so I'm going back to the good stuff.

Is there any harm in going back to r-12 after I ran r-134a?

[philip]

SNIP
Is there any harm in going back to r-12 after I ran r-134a?

But for the general knowledge that mixed R-12 / R-134a (especially with contaminated lubricant) is corrosive to rubber, I do not have a qualified answer to your question.

Changing refrigerants

Changes in A/C refrigerant oil: As a rule, R-12 systems use mineral oil and
R-134a systems in new vehicles (OE Applications) will use PAG oils. For compatibility
issues, the industry moved to use Ester oil (POE) for retrofitting systems.
Ester oils were chosen because they were shown to be compatible with both the
mineral oil already in the system and the R-134a refrigerant about to be installed.
In recent years, new synthetic lubricants have been introduced that have proven
work well with all oils. They have shown excellent results, improved cooling
performance and have eliminated a lot of the confusion about which oil to use
and when.

Flushing the A/C System: This is usually done in order to remove as much of
the mineral oil (and any other contaminants) in the system as possible. It also
helps to assure against oil overcharging which can reduce cooling performance.
When the system is flushed, the proper amount of new oil can be added before
recharging. If your are considering retrofitting your a/c system because some
other component has failed (ie.: leaking evaporator, compressor failure, etc.)
the system should most certainly be thoroughly flushed.

Change of drier or accumulator: The drier or accumulator is the one part that
should always be replaced when retrofitting. First of all, it provides filtering
for the refrigerant and (most importantly) removes moisture. Doing a retrofit
without it would be like changing the engine oil and not changing the filter.
Secondly, new replacements will (almost always) be manufactured with either
XH-7 or XH-9 desiccant. These are compatible with R-134a while the desiccants
used in R-12 systems may not be compatible.

[philip]

SNIP
You've got some kicka$$ system if you can pull a 68 deg. differential! Is this in recirculate mode? You running some kind of magic freon you got from south of the border from the back of some guy's van along the side of the road?

"redmondjp": I took this today while driving south on I-15 past Sun City.



Getting closer to home agian ... switched off the a/c. Normalized:

[asavage]

I agree with JP: that's an incredible temp split. As in "not credible". If it wasn't you claiming it, I'd cry foul.

I've never (before) seen better than 50°F split, and I consider 40° "good", 45° "exceptional".

[philip]

I agree with JP: that's an incredible temp split. As in "not credible". If it wasn't you claiming it, I'd cry foul.

I've never (before) seen better than 50°F split, and I consider 40° "good", 45° "exceptional".

There are a couple of things about this OEM system that are noteworthy.

The condenser while of small dimensions, does have deep flat serpentine tubing instead of round tubing. The evaporator is old school in that it has 6 parallel round tubing circuits instead of brick construction containing numerous, single pass, parallel, flat passages.

The FSM details the correct way to recharge this system from an evacuated state which ensures correct liquid / gas ratio thereby avoiding excessive high side pressures at given ambient temperatures.

Air and/or too much oil are two things often present in systems where the car owner has been refilling a system having leaks. The system must have NO AIR and just the right amount of oil.

[davehoos]

I work as an airconditioning specialist in Newcastle NSW. It's on the coast where humidity is medium/high. Inland from here ambient temps can be high.

We only use R134A as a replacement gas and use PAG oil in passenger cars. Other types can cause warranty issues. Extreme low temp industrial units use other types of oil/gas combinations. Replacement expansion valves and dryers are normally recalibrated to suit R134A. We don't flush systems as a rule but, we blow out "excess" oil if needed. If oil comes out the condensor/evaporator easily then my thoughts are than it would have flowed with the R134A reducing the capacity.

A/C is more of an art than a science. I know engineers will not like this statement but some refrigerants work and some do not. For example, I recharged a car today that gave perfect pressure levels. It was serviced by a panel shop as part of paint repair. The system contained Hydro carbon 2%,R12,R134A 96% and a small amount of air. All metal pipes showed no real temp changes tested with my hand. You often see this with blended gas. The good bit settles to the top of the charge station and/or leaks out of the car system, leaving weak refrigerant or air.

Copper evaporator compared to alloy can take a long time to feel cool. These are rare today but some component manufacturers will supply copper for high humidity areas like Darwin NT. Alloy units can have a 2 year life span in these areas.

The drama you have getting suck-through-evap to cool evenly over a long trip is simply not worth the hassels. I think the USA 720 would be of the conventinal set up. Suck through systems are common in Datsuns in the 70-80's. These obviously built without a/c in mind. Aftermaket suppliers often add a fan to operate when used.

The modern parallel flow condensers are tiny compared to the old Modine and copper tube units. The transfer heat much better if the air flow is reasnable. I have replaced large Modine units with much smaller parallel flow type find that cabin temp is very low at low rpm.

I'm not fussed with the new subcooler system but they work if full of refrigerant.

Most systems need to cycle to get the best out of them. The compressor turning off allows water to be drained from the evap, and oil/liquid returning to the compressor. I dont like to overcool the returning liquid, I find expansion valve works better if there is a bigger pressure drop. I like the valve to show signs of adjustment due to the cold sencor on the outlet pipe but many don't. In not fused with external equalised valve but I'm using a oil return that is the same basic setup..

Extra insulation on the low side rubber hose is not warranted. The oil needs to flow and can freeze in the suction pipe. The compressor must be big enough without stalling the engine and suit the engine. The vane pump used on later models is more like the modern scoll pumps and are used to reduce fuel/power use.

2 modern small compressors are better than 1. I like the big variable displacement pumps as i like to see it working at low engine speed. Getting the right size pump to expansion valve is critcal. Original genuine parts[no longer exist],probably set up to compromise for use in all temp zones, this can't work. I like the delphi/harrison/calsonic compressor also the large sanden units. The V5 and later units work differently to the sanden Sd7H16V, but are similar. I find the sanden is a little slower to change cabin temps. Both make similar items that bolt on the same mounts. I haven't found any cheap V5 units laterly, I have a few dead units that i can swap internals. I am told they are common in Europe.
I bought a scrap V515B of a U12 bluebird. I am told they are common on infinity cars.

[philip]

I work as an airconditioning specialist in Newcastle NSW. It's on the coast where humidity is medium/high. Inland from here ambient temps can be high.

My driving territory runs from the Pacific Ocean in southern CA to Death Valley. So relative humidities can range from socked in coastal fog to %5, relatively speaking.

We only use R134A as a replacement gas and use PAG oil in passenger cars. Other types can cause warranty issues. Extreme low temp industrial units use other types of oil/gas combinations. Replacement expansion valves and dryers are normally recalibrated to suit R134A. We don't flush systems as a rule but, we blow out "excess" oil if needed. If oil comes out the condensor/evaporator easily then my thoughts are than it would have flowed with the R134A reducing the capacity.

As a repair shop in Australia, are you legally prevented from recharging an older R-12 system with R-12?

A/C is more of an art than a science.

Agreed

I know engineers will not like this statement but some refrigerants work and some do not. For example, I recharged a car today that gave perfect pressure levels. It was serviced by a panel shop as part of paint repair. The system contained Hydro carbon 2%,R12,R134A 96% and a small amount of air. All metal pipes showed no real temp changes tested with my hand. You often see this with blended gas. The good bit settles to the top of the charge station and/or leaks out of the car system, leaving weak refrigerant or air.

I learned my lesson long ago about those "environmentally safe" R-12 replacements and the resulting compromise from using R-134a in an R-12 system. I don't want my A/C sticking it's tongue out (going warm) when ambients are 100 degrees plus!

Copper evaporator compared to alloy can take a long time to feel cool. These are rare today but some component manufacturers will supply copper for high humidity areas like Darwin NT. Alloy units can have a 2 year life span in these areas.

Agreed. There is a LOT of metal in copper tubing evaporators that need chilling first.

The drama you have getting suck-through-evap to cool evenly over a long trip is simply not worth the hassels. I think the USA 720 would be of the conventinal set up. Suck through systems are common in Datsuns in the 70-80's. These obviously built without a/c in mind. Aftermaket suppliers often add a fan to operate when used.

I disagree with your assumption. My truck has factory (not dealer) installed A/C. The compressor is unique as is the engine's air induction system over the a/c compressor, condenser design, and all the underhood pressure lines compared to the dealer installed kits of the era.

The modern parallel flow condensers are tiny compared to the old Modine and copper tube units. The transfer heat much better if the air flow is reasnable. I have replaced large Modine units with much smaller parallel flow type find that cabin temp is very low at low rpm.

As I mentioned earlier, the Datsun has the old school copper tubing evaporator.

Most systems need to cycle to get the best out of them. The compressor turning off allows water to be drained from the evap,and oil/liquid returning to the compressor.

Water drains off the evaporator's surface continually. There is no need to shut down the system for this to occur. Next, once compressed liquid and oil find their normal RUNNING levels, what is your reasoning for shutting down the system? (Leaving OUT for the moment a separate discussion about evaporator icing).

i dont like to overcool the returning liquid,i find expansion valve works better if there is a bigger pressure drop.i like the valve to show signs of adjustment due to the cold sencor on outlet pipe but many dont.in not fused with external equalised valve but im using a oil return that is the same basic setup.

I am in the other camp. Better to have cool liquid refrigerant coming out of the reciever/drier and with that, lower overall pressures. I take it you look for the Hi side / Lo side ratio instead.

The extra insulation on the low side rubber hose is not warranted the oil needs to flow and can freeze in the suction pipe.

There is only 18" of rubber hose on my low side. The remaining 6-7 feet is aluminum tubing which I insulated from engine heat. In spite of the added insulation, note the heat gained between the evaporator exit and the compressor inlet here

So, (1)at what temperature does R-12 spec mineral oil turn to thick gel and (2)do you believe the low side line achieves that temperature?

[davehoos]

There is no legal reason for not using R12. retro fitting is not mandatory. I believe it in common use with appliance goods and large cooling rooms/beer chillers. R22 is still around a few years and we use a lot of R404. it is illegal to import or manufacture so reclaimed R12 is cleaned and sold at silly prices. few hundred $ per car vs $15-20 and $40 for oil. i had dramas importing an R31 this year as it did not have paper work to show the a/c had been inspected.

im guessing there may be a legal restriction for using R12 in a R134a designed system-or a vehicle built after the changover date i think its a new model 1993[?].

Modern hoses are different they have an extra lining inside. but a 20 yr vehicle should be due for replacement. the low side hose will hang in for many years past it due date. this is a large volume of the work at the workshop. cutting of the hoses and wielding in barbed ends to allow replacment hose sections.

Extra fan.
I was refering to the evaporator. australian built datsuns use smiths heater systems. these are often used in other areas of the world. 1980's 910[maxima] sold in australia had the smiths unit while the japanese had a more conventional diesel-kiki. the smiths a/c has a large evaporator the size of the glovebox area and the fan is near the clutch pedal. this is a suck through. a lot of after market companies add a 10 inch fan to the air intake side to push air through.you see these on 1970's datsuns. some older cars like the new VW transporters add the fan and run piping to the center face vents

Most evaporators trap water on the metal surfaces. with large fridge units you look at the frosted pipes to judge the liquid quantity as the site glass clears long before the system is full. if the condensor is not big enough the site glass will go milky then bubbles will apear. this is sometimes just hot oil.

New systems don't look at evap core temperature(below -6°C / 21°F), just air temp 1 inch from the core (normally 1-2°C with 2° gap) or the accumlator system low pressure cycling switch (18-30 PSI). this gives 2.5-10°C deg (36-50°F) duct temp. up market cars will add core temp or intake air temp to judge defost needs. i find that little japanese cars do this well. some have a delayed restart of the compessor. explaining the need to defrost the system to new car buyers, and that annoying customer complaint that it didnt do it before i serviced it. SINCEUWORKEDONIT.

I read that R12 has a 5:1 ratio and R134A has a 7:1 ratio. not seen this myself. I look at the low side/vent temp ratio - with very low pressure
the pump will die. customers dont like that. oil return is a problem easy to allow for or fix. im told that mineral oil tended to stay in the pump. I dont know. i like a TX system without external equalisation to have around 5-10 PSI. an accummulator system will have 20-40 PSI and control valve pumps destroke at 40-50 PSI.

the high side should have pressure/temp cut outs. some hot days are enough to trip the sencor without the pump turning on. many common sold cars have an independant fan switch that operates at 250-350 psi.
if this is the case convert to R404. with R404, at rest pressure can be 200+psi. Running, high side 450+psi: low side 10 psi.

i looked up my 1973 leyland P76 book-
R12. york 8.7 inch. ambient temp 100F
220 psi:29 psi gives 30F evap temp.
1500RPM. that not 5:1.

oil return is a problem. the factory setup should be OK. we often do freezer units for light trucks that use the cabin a/c as well. in cold frosty mornings we often get siezed pumps on initial start up. my 1989 falcon is the last of it kind with old thermostat. over night frost 32F temps are enough to trip the thermostat and must wait till the heated air warms up the evap core to switch on the compressor. the later electronic models wait for water temp at the heater core to allow the climate control to work. accumulator fitted cars often have the alloy accumulator next to the exhaust or radiator to heat the returning gas. new denso system runs the spiral liquid line inside the suction line.to cool the condensed liquid and heat returning oil.

gassing vehicles.
the book shows that heating the bottle or pumping in set amount of gas is the way its done. this is ok if its standard vehicle. puting in liquid from a bottle can cause hydrolic lock or freeze shatter the reed valves in the pump. its easy to do. same deal with a vehicle in cold weather. the accumulator systems are good for this purpose. liquid is at the bottom and vapour is drawn from the top. however a change of state heat imput is required so insulating is not a good idea. some systems water heat this. with r134A an oil return system was added the suction side, the accumilator has a loop of pipe with a oil filter and orifice setup at the bottom vapour is drawn in at the top. this system is used to keep the evap full of liquid not vapour as in a expanion valve setup..

[philip]

Dave: Much of your post is beyond the scope of R-12 systems fitted to Datsun/Nissan 720 trucks. So let's keep focused.

SNIP-
Modern hoses are different they have an extra lining inside. but a 20 yr vehicle should be due for replacement. the low side hose will hang in for many years past it due date. this is a large volume of the work at the workshop. cutting of the hoses and wielding in barbed ends to allow replacment hose sections.

The workshop splices new hose sections into old hoses? Those barbed fittings with a couple of hose clamps are more vulnerable to failure than a new hose with swedged fittings.

SNIP
Most evaporators trap water on the metal surfaces.

All automotive evaporators "sweat" (water condensation on the outside surface of the LO side vapor passages) at some point above freezing (32°F/0°C). This "sweating" flows to the ground freely & continuously. The evaporator core temperature sensor cuts OFF the compressor clutch just above this temperature to prevent the core from becoming a block of ice. ONLY in VERY arid climates are these sensors calibrated to a lower temperature. Unfortunately in vehicles with these sub freezing sensor thresholds, your customer WILL experience evaporator ice-ups when ambient humidity is high ... say above 40% relative humidity. That's when cooling fades away and the driver needs to thaw out the evaporator.

New systems don't look at evap core temperature(below -6°C / 21°F), just air temp 1 inch from the core (normally 1-2°C with 2° gap) or the accumlator system low pressure cycling switch (18-30 PSI). this gives 2.5-10°C deg (36-50°F) duct temp. up market cars will add core temp or intake air temp to judge defrost needs. i find that little japanese cars do this well. some have a delayed restart of the compessor. explaining the need to defrost the system to new car buyers, and that annoying customer complaint that it didnt do it before i serviced it. SINCEUWORKEDONIT.

See previous paragraph of mine.

I read that R12 has a 5:1 ratio and R134A has a 7:1 ratio. not seen this myself.

I am not surprised. With the correct balance of R-12 refrigerant liquid to refrigerant gas, the 5:1 (HI side to LO side) ratio (or a bit less) will be achieved. Same to be said about R-134a. When the balance has excessive gas, high pressures soar and cooling decreases. Excessive HI side pressure is hard on the compressor and magnetic clutch. HI side hoses sometimes blow.

I look at the low side/vent temp ratio - with very low pressure the pump will die.

If I understand this "correlation" correctly, your high side pressures are ignored? So ... what is the optimal "low side/vent temp" ratio you aim for in an R-12 system?

SNIP. The high side should have pressure/temp cut outs. some hot days are enough to trip the sencor without the pump turning on. many common sold cars have an independant fan switch that operates at 250-350 psi.

Another indication of system over charging with R-12, likely excessive refrigerant gas, or failure to dissipate heat has occured.

if this is the case convert to R404. with R404, at rest pressure can be 200+psi. Running, high side 450+psi: low side 10 psi.

I would NEVER follow this refrigerant replacement suggestion. Not ever, regardless be the refrigerant R-12 or R-134a. The reasons are obvious.

i looked up my 1973 leyland P76 book-
R12. york 8.7 inch. ambient temp 100F
220 psi:29 psi gives 30F evap temp.
1500RPM. that not 5:1.

At 100°F, what actual HI/LO pressure and DUCT temperature readings do you achieve in that vehicle? And at what relative humidity?

SNIP-
gassing vehicles. (aka "recharging")
The book shows that heating the bottle or pumping in set amount of gas is the way its done.

Clarification. When recharging from an evacuated state, the Datsun FSM says to warm the charge can in warm water for only a few minutes ONLY WHEN the system is slow to take refrigerant. This slow acceptance indicates too much gas / pressure has been put into the system.

SNIP- Putting in liquid from a bottle can cause hydrolic lock or freeze shatter the reed valves in the pump. its easy to do.

This is a half truth. The FSM dictates (1)the compressor is NOT running while refrigerant is being installed into an evacuated system and (2) that BOTH pressure gauge service valves are OPEN to admit gas refrigerant.

What you say would be true (risk of damaging compressor valves) were one to admit liquid refrigerant into the LO side only with the compressor not running as the suction reeds would be pushed open thereby permitting liquid into the compressor. Damage can also occur by suddenly admitting a large dose of liquid refrigerant to the LO side while the compressor is running.

What you seem to have missed is that the FSM outlines the process for charging the system from an evacuated state with liquid only (inverted charge can). This is done through the HI side ONLY with the compressor NOT running. Liquid refrigerant will not flow into the compressor due to the outlet reed valves. Also, any liquid present when the system is turned ON will be located on its way to the condensor ... as it is normally. Recharging an evacuated system this way ensures the correct balance of liquid-to-gas. The final refrigerant "topping off" is then done with gas admitting through the LO side with the compressor running. This is often less than half pound of refrigerant.

same deal with a vehicle in cold weather. the accumulator systems are good for this purpose. liquid is at the bottom and vapour is drawn from the top. SNIP

Again, in the context of Datsun truck with R-12. I'm not understanding what you mean by "accumulator."