I have a 1986 Dodge D150 pickup. The A/C does not work. The R12 refrigerant is either low or completely leaked out. The compressor clutch will engage when the low pressure valve is shorted. Nothing shows in the dryer sight glass. All of the A/C components appear to be original. Since I just bought the truck I don't know when the A/C last worked. Should I replace all of the A/C components (compressor, dryer, condenser, expansion valve) before I even try to recharge refrigerant with R134a? I'm afraid that I would just waste the cost of a recharge with the old components in place. Any advice would be appreciated. Thanks.

Hi,well at best you`ve got a leak in the system,so you need to diagnose that first,a couple ways you can start,hook a vacuum pump up to the system and see if it will hold a vacuum for an hour or so,if it does then the leak is either very small or maybe no body ever serviced the unit,it may be low on oil,could have dried seals, the other way is to put a charge of freon in the system and start looking for leaks,it would probably help if you had a freon detector so you could check the connections and condensor,evaporator for traces of the gas,but I don`t think just taking the shotgun approach to replacing all the parts first without a plan to diagnose is the best way.
just my opinion.

A UV dye and a UV light work great in finding leaks....

You just have to clean everything beforehand and charge it up........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Groovy picture, man.

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Casually looking for a Clifford hyperpak intake for cheap.

Our resident expert on AC is Charrlie S. PM him and get his advice on your system.
JMHO
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

In the case of the OP, this would be difficult. To use UV dye, it is necessary to run the system. His system is still r-12. Don't want to waste r-12 to leak test. To use r-134a need to change the compressor oil, which requires removeing the compressor. Why do that, when the compressor may be the leak.

I have so much equipment available, it is sometimes hard to figure a DIY method. I think what I would do (as a DIY) is get some "freeze12" and charge the system. Before charging, disconnect a line and install some dye. Then run the system and look for the leak. I do not reccommend using "freeze12" as a refrigerant in a car. just for leak checking.

It might actually be better to pay an A/C shop to do a system check. Because you still need a vacumm pump, and Gauges, and the UV light or electronic leak detector .
If you don't have this equipment, it can be quite a bit of money.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Assuming you're going to flush the system and replace the oil and drier afterwards......

Is it possible to add some dye, then pressurize the system with N2 or CO2 (about 30 psi), run the system briefly to circulate the oil and dye; then look for the dye with a UV light?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

To presurize the system with N2 or CO2 first you need the tank of gas, these are actually very inexpensive. The pressure regulator is the pricy thing, about $90-$100. With dye the system has to run for awhile to circulate the oil/dye, and give it a chance to leak out. But you don't want to run the compressor at all, because it will jack the high side pressure to the point of blowing a hose. If you have N2 or CO2 available, just add a little refrigerant (1/2 lb of any type) and and pressurize (less then 125lbs)the system with the gas, and use an electronic leak tester. That is what I do for hard to find leaks.

Or you could charge the system with propane, and search for the leak with a match.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225