[allenga]

Guys, My AC was resurrected last summer. New hoses, new clutch, new oriface tube, new o-rings. R134. It short cycles at any RPM and when the outside temp is at 100 or 50 F.

I bought it back to the same shop 4 times and they can't solve it. They say pressures are normal.

Any thoughts.

Thanks

https://youtu.be/iZ0QnniBd9U

[Pepi]

Typically sounds like low charge, but if you say pressures are normal, that tends to rule that out unless you are on the low side of normal.
When you say it was resurrected last summer; what was wrong with it that it wasn't working before then? Did you replace the receiver/drier? Was the system flushed out and a good vacuum pulled to remove any moisture?

[allenga]

The AC was not used for several years by prior owner, it would not hold a charge. The receiver/drier was replaced by prior owner to convert from 12 to 134. I fixed all the leaks.

The system was flushed, evacuated and refilled several times.

[Pepi]

If the system was leaking and everything leaked out, then that meas atmosphere air got in, along with moisture. The desiccant bag probably is ruined and not removing moisture from the system. That could cause evaporator freeze ups also.

[allenga]

Originally Posted by Pepi

If the system was leaking and everything leaked out, then that meas atmosphere air got in, along with moisture. The desiccant bag probably is ruined and not removing moisture from the system. That could cause evaporator freeze ups also.

desiccant bag?

[Pepi]

Receiver/Driers have a desiccant bag in them to remove moisture from the system.

[allenga]

ok. Would that cause short cycling as soon as I turn the car on.. Thanks

[Pepi]

That I am not sure about..

[Goatracer1]

Does your system use a cycling switch? If so possibly a miss located or bad switch?

[PunchT37]

Is the orifice tube designed for 134? It`s larger than a 12 one. The 134 molecule is bigger than the 12. So, if the tube is wrong, the Freon has a hard time passing through the too small of an orifice. This causes a vacuum on the low side. So, the pressure switch sees the low pressures and kills the compressor.

If the switch is adjustable, set it to cut off at 18 to 19 pounds with the 134. 25 is too high, especially on retrofits.

[allenga]

Originally Posted by PunchT37

Is the orifice tube designed for 134? It`s larger than a 12 one. The 134 molecule is bigger than the 12. So, if the tube is wrong, the Freon has a hard time passing through the too small of an orifice. This causes a vacuum on the low side. So, the pressure switch sees the low pressures and kills the compressor.

If the switch is adjustable, set it to cut off at 18 to 19 pounds with the 134. 25 is too high, especially on retrofits.

Thank you Sir. I will look at it. My low pressure switch is not adjustable.

[PunchT37]

Originally Posted by allenga

Thank you Sir. I will look at it. My low pressure switch is not adjustable.

Find one that is and set it as stated above.

Been here done that on a `79 Trans Am. Those older cars have a hard time getting rid of the high side heat as well. Those systems were designed for 12. Have a good thermostat style HD fan clutch.

[allenga]

Thanks Punch. I just upgraded radiator, water pump and therm fan clutch.

I'm frustrated. I had a guy from the 70s, grey haired guy ASC master and he could not figure it out or make recommendations.

I will find the switch and bring the car back. :-(

[PunchT37]

Forgot to add, when using 134 in a 12 system, only use 70 to 80 percent of the recommended 12 fill.

[PunchT37]

Originally Posted by allenga

Thanks Punch. I just upgraded radiator, water pump and therm fan clutch.

I'm frustrated. I had a guy from the 70s, grey haired guy ASC master and he could not figure it out or make recommendations.

(

I used to work with an ASE Master Tech. He had the gold plaque on his tool box. He couldn`t find his ass with both hands and a road map.

We called them book worms. They can pass a test but, put em a shop in the real world, and ask them to think.

[LATECH]

Hmmm.

I have ASE A1 through A8 I am also L1 certified. I have a PA safety and emission License I have been certified for 35 + years and have been wrenching on cars for about 38 years

Retro fitting to 134 requires around 85% of the same charge as R 12

Yes on the adjustable Low pressure switch

The 134 molecule is actually smaller than the R 12 molecule. It is its thermodynamic transfer ability that requires a larger Orifice, as for 1 the pressure will be a bit higher on the low side with a smaller orifice

Also the larger size gives a bit more flow so it can move heat a little faster

That helps to make it cooler.

I had a woman who owned a repair shop (old subaru dealer shop)

I went to her for a job years ago. She offered me a laughable wage and said That ASE certs dont matter. Anyone can get one.

Like I said .I have 9. I averaged 93 percent across the board on it all.
I aced the 80 question Electronics test.

I am not insulted by your statement, but I did want to set the record straight.

Maybe you should try taking the test to see what it really is about, and Post your scores.

[LATECH]

MackFri®-134a refrigerant. Chemical formula CF3CFH2 (tetrafluoroethane). R134a molecule has smaller size than R12 molecule which makes danger of leakage more considerable. Ozone depletion potential ODP=0, global warming potential GWP=1300. Physical qualities of R134a are given in table below.


http://www.allchemi.com/eng/refreger...kfri-134a.html

[allenga]

Thanks. Original Air does not stock an adjustable low pressure switch for a 77 TA 400 auto. Anyone have a lead. Thanks!

[PunchT37]

Originally Posted by LATECH

Hmmm.

I have ASE A1 through A8 I am also L1 certified. I have a PA safety and emission License I have been certified for 35 + years and have been wrenching on cars for about 38 years

Retro fitting to 134 requires around 85% of the same charge as R 12

Yes on the adjustable Low pressure switch

The 134 molecule is actually smaller than the R 12 molecule. It is its thermodynamic transfer ability that requires a larger Orifice, as for 1 the pressure will be a bit higher on the low side with a smaller orifice

Also the larger size gives a bit more flow so it can move heat a little faster

That helps to make it cooler.

I had a woman who owned a repair shop (old subaru dealer shop)

I went to her for a job years ago. She offered me a laughable wage and said That ASE certs dont matter. Anyone can get one.

Like I said .I have 9. I averaged 93 percent across the board on it all.
I aced the 80 question Electronics test.

I am not insulted by your statement, but I did want to set the record straight.

Maybe you should try taking the test to see what it really is about, and Post your scores.

I thought someone would get offended by my statement. As usual. I know ALL master techs are not book worms. But,the guy I was referring to was. Just because one has certs doesn,t make em experts. That goes for all certs, not just auto certs.

I,m out of that game now. But, I started turning wrenches, for a paycheck, in 1985. My ASE certs are long expired.

I got out in 2008. So, I'm rusty. I pulled wrenches at a water plant for 5 years after that and now I am an operator. I pull wrenches for a hobby or side hustle now.

[PunchT37]

A flow restriction at the orafice is gonna cause a much lower pressure in the evaporator and back to the compressor. This causes freeze ups and rapid cycling.

So, I got the molecule thing wrong. But, I do know a little about cars.

It's all good. I got out because I know how most are treated/paid in this business. Especially if you work for the man and don't have your own shop. Then, it's got it's problems.