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A/C mike C info

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#1 importwarrior


    6 Quests and Counting......

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Posted 07 August 2015 - 09:22 AM

Information provided by

Mike C

First, repair whatever caused the original a/c leak/failure before recharging... otherwise your new refrigerant will just leak out again.  Most a/c leaks will accumulate a wet/greasy mess. Look at the joints in all of the a/c hoses/pipes for messes. If grease is everywhere (as is common on older cars) then you'll have to clean all the joints and re-fill one more time. A pro shop might do exactly this - with a ultraviolet (UV) dye added. Simple Green works well to cut through most engine grease by the way.

Usually, when I have a leaking o-ring seal on a car a/c system, rather than fixing only the bad joint, I replace every o-ring in the system: if one is old enough to have died, the others are probably on their last legs too. I'd rather do the work once and not have to worry about leaks for another 10 years. I often replace the rubber hoses too.

O-rings eventually fail and leak. The hard rubber a/c hoses often get hard/brittle at their ends, where they fit into those crimped-on caps. If you've never seen how a high pressure hose fitting works, it's basically:
* Metal pipe threaded on one end (with the o-ring trapped in there) to mate with the another pipe.
* That metal pipe ends in a barbed pipe.
* The rubber hose fits tightly over the barbs
* Instead of using a typical hose clamp, a cylinder shaped metal piece is used. This fits over the end of the hose; a special tool crimps grooves into this cylinder... the grooves are spaced similar to the barbs of the inner pipe. This makes a really tight seal.

Unfortunately, when the rubber gets old and dries out, it shrinks a bit so the outer cylinder doesn't clamp as well. Flexing the hose (which happens when the engine "leans" as you rev it or start it) exacerbates this problem. Often you can "test" a hose by flexing it near the outer cylinder, listening for leak sounds.

There are a few o-rings in the evaporator core - the radiator-like part under the dash (typically) that actually cools the air. These o-rings aren't subjected to engine bay temps so they fail far less often - which is fortunate because replacing them is a big labor expense. You may gamble on not replacing them when doing all the others... it's a pretty safe bet.  Also under the dash on StarQuests is the "expansion valve" which is what makes the high pressure refrigerant jump down to a low pressure - and jumping to a really low temperature too.  The factory StarQuest R-12 specific part works okay for R-134a but you can buy aftermarket ones that are designed for R-134a.  Pay attention to the "bulb" part and how it's hog-tied to one of the refrigerant hoses; you'll want to make sure the bulb on the new expansion valve is installed the same way.

To do the job yourself, and to do it right, you'll need to be able to:
1: safely/properly unbolt each joint. Usually simple - just use two wrenches just like any plumbing job.  Take the hoses & pipes out where possible and hang them vertically - this will drain the old R-12 compatible oil out of the system.  

2: If the rubber hose joints leak, take the hose to an a/c shop, NAPA, etc. and have the rubber part replaced. They'll slice the metal cylinder sleeve apart, replacing the sleeve and the hose with new "barrier" style hose - required for today's R-134a refrigerant but compatible with the old R-12 freon as well. They'll re-use only the original barbed fitting/pipes on each end.  Old rubber a/c hoses are too porous for the smaller R-134a molecules... though once coated with R-12 and oil that often seals the old style hoses pretty well.  That's why folks that don't fully convert get 2=5 years out of a R-134a charge anyway.  Again though I like new, pliable hoses instead of old brittle ones that may fail any day.

3: Use R-134a rated o-rings - basically blue or green ones. They'll work with R-12 as well. The black ones are too porous for R-134a. I'd replace the receiver/dryer too; they have a finite lifetime.  That's the silver canister strapped to the nose of the car near a headlight.  It "filters" crud from the refrigerant... so it's easy to see why it eventually is used up.

4: when re-assembling, wet the o-rings with a/c system oil as you install them. Otherwise they can rip/tear as you tighten the joints.  R-134a retrofit kits will include a couple of adapters to screw onto the original a/c service fittings (the fittings where you hook refrigerant cans and gauge sets).  R-134a fittings are a different size from R-12 --> to prevent accidental miss-matching refrigerants.  You'll need to remove (unscrew) the valve tip from the original fittings first.

5: with the system totally assembled, connect an a/c pressure gauge set (two gauges).

6: Ideally the system would be flushed out with nitrogen. This helps flush out any moisture from the atmosphere that might have gotten into the system.  Shops do this; many home mechanics can't/don't because they don't have nitrogen tanks handy.

7: Pour or inject the proper quantity of a/c compressor oil into the system. There are two types of oil: one for the old R-12 refrigerant and one for R-134a. Use the one that matches the refrigerant... even if your car WAS R-12 originally and you're converting it to R-134a you'll need oil compatible with R-134a. The oil is "picked up and carried by" the refrigerant; R-134a won't carry the older oil.  Pour the new oil into the gauge set's hose going to the "discharge" or "high pressure" side of the compressor.

8: Apply a vacuum pump to the system and fully evacuate it - takes a minimum of half an hour in most cases. Then shut off the vacuum pump. Let the system sit for some time - hours if possible - and verify the gauges don't budge. If they move, you still have a leak.  If you didn't use nitrogen, run the vacuum pump much longer - it takes a while to get all moisture out of the system under vacuum.

9: Connect the gauge input hose to a source of refrigerant. Leak a little of the refrigerant where the hose joins the gauge set (loosen the fitting slightly while the refrigerant tank is open) to flush air out of that hose. Then re-tighten the input hose. Open the gauge valves and allow refrigerant to flow from the pressurize refrigerant tank into the car. Pro shop equipment will measure the weight and/or volume of the refrigerant so they know how much went into the car. You'll probably just count cans of refrigerant. If using the cans, stick them into a pan of hot (but not boiling hot) water; that'll raise their temps and thus the refrigerant pressure in the can so you can get more out of each can.

10: once one can is in the system, close the gauge valves, fully open the needle valve on the refrigerant can, then remove the can, and replace it with a new/full one.

11: Turn on the engine and set the a/c to max cool, lowest temperature, full recirculate. There should be enough pressure in the system for the a/c compressor to engage: StarQuests (like most cars today) will NOT run the compressor if the refrigerant pressure (and thus refrigerant quantity) is too low because no refrigerant flowing through the system = no oil flowing with the refrigerant either.

12: stick a thermometer into a center dash vent. Monitor the air temps coming out of the system as you fill with the second refrigerant tank.

13: the factory service manual for the car, or the manual that came with the gauge set, will show the proper "suction side" and "discharge pressure" for your a/c system as a function of outside/ambient air temperatures. Use these as a guide... adding refrigerant until your gauges indicate those pressures. You'll probably need a helper to hold the engine RPMs up a little. Watch the thermometer we stuck into the dash vents... if that temp starts rising, the system has just passed "enough" refrigerant.

Factory R-134a systems use a larger condensor (the a/c radiator in front of the engine) than an equivalent capacity R-12 system.  You can either replace the stock condensor with a thicker one (if you can find one...) or tweak the electric fans.  I re-wired one car's pusher fan to run whenever the a/c system is ON; on a stock StarQuest it only runs when the a/c is working extra-hard.  On my car I didn't bother with this and the a/c works fine anyway.

mike c.

B-71 87 TSI ~ RIP

Black 87 Starion ~ Mess SOLD!!!

Proud New 89 slightly Rusted Fiji Owner !!!

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