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Discussion Starter #1
Sounds boring but I bet there is someone out there with the knowledge.I am restoring the A/C system on a '71 Firebird.Both ventilation boxes where removed from the car,completely cleaned,inspected,and reassembled.Quite a task with all the vacuum lines and unusual electrical circuit.Once we recharged with gaz and turned the system on,the circuit got externally icy from the receiver-dryer all the way to the POA suction valve.From that point on it was warm.The evaporator was not cool.Pressures on high and low sides where correct.According to the troubleshooting manual ,this POA valve can not be opened or serviced.I can not find a new one.Any hints?
 

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sounds like the receiver dryer is pluged up and is acting as a expansion valve, but the preasure on the low side should be low. What kind of refrigent are you useing? Not that it matters at this point but mabey later, can you check preasure AFTER the receiver D.? if so and the dryer is puuged the preasure will be low, below fifty#. Good Luck.
 

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Discussion Starter #3
Thanks for answering! Well,this Firebird had been without A/C for at least 6 years.I decided to buy all new items.Condenser,hoses,dryer and compressor.The only old items are the evaporator,Exp valve and POA valve.The evaporator was tested outside and is OK.My A/C man came to my garage and charged the system with some new 3rd gas that I do not recall it's name/number.It is priced in between Freon and 134.It uses the same Texaco Capela oil and regular O rings.

At first the Low side read more than 30 psi and than went to low 20s.We are building that fixture with fittings to test a Exp valve outside the car.You know,high side hose directly into valve,out let to low side hose,balance tube into T,and other T for calibrated hole and finally fitting into low side gage.Than dip bulb into cup of ice and cup of warm water to make the Exp valve move from minimum flow into max flow.And read pressures.

Being that you work in this field,is the original POA valve still available?

Thanks Paulo
 

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I haven't tryed to buy a POA in years. Surely some one has some somewhere, it's not like they only used it for three years, like the VIR system, Ford even used the POA for several years they had a motot craft part number but GM just the same. I'll check oround and see if their are any locally. I know you are restoring this car, but I put A.C. in my motor home two years ago without a receiver dryer or accumlator. It's a 73 and for my own use but it works just fine. Just a thought, all you need is an orfice to get cold air. Good luck.
 

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could not find it local but did find one in Nashville GA. From obsolete Chevy. Part#50-2551A for 134A ref.Cost106.20. Phone 229-686-5227. Mabey that will help. Good luck.
 

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Discussion Starter #6
Ok,thanks again.I spoke with my A/C guy today.He says the gas we are using is called MP 39.The newer model compressor we got is a Nipondenso.More compact than the Frigidaire.Threads for Freon,not 134. I will phone to this shop you mentioned.Maybe they have the POA for Freon or this MP 39.
 

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MP-39 apparently works better than R134a to replace R-12, but MP-39 is not really intended for automotive appplications. It more commonly used for stationary coolers in stores. I'm not sure why its not used in automotive A/C.

The one advantage of R-134a over most other choices is that it is the most common replacement for R-12. If you want someone to charge your A/C, they have to be able to recover the refrigerant, and most auto shops can only recover either R-12 or R-134a.

I had good luck with the conversion of the A/C in my '75 GMC pickup, using a new Seltec compressor, new parallel flow condenser, and R-134a with a Ford blue orifice tube (smaller orifice than the original GM white orifice). I charged the system with R-134a at 80% of the original R-12 charge. My vent temps are about 35 degrees when ambient temp is about 85-90 degrees.

Bruce
 

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Discussion Starter #8
OK Bruce.Yes I remember well when the new laws concerning A/C pollution got into effect.I was living there.Around '89 the sale of Freon in cans became forbidden.Then the recovery stations became mandated.See,around here in Brasil only now they are talking about phasing out Freon.Maybe that is why this MP 39 can be used on motor cars.
I am trying to stick to the original system.The expansion valve can be partially serviced,but the POA can not.And it seems to be a complex one.Your '75 model probably had a VIR system,which had a very short life.Outlet cooling to 30s? Congratulations!
Besides Four Seasons/Standard,what other companies sell A/C components?
 

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Four seasons seems to be one of the most common brands, and their products are also often relabeled and sold by other companies. Transpro and Visteon sell condensers, and there are still many replacement parts available from Delco.

If you can locate some of the Delco or other AC parts catalogs online, they have a lot of useful information. I've run across the Delco information online, but didn't keep track of where I found it.

Bruce
 
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