Tuesday, January 18, 2011

Fixing Your Muscle Car A/C

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The article featured on this page is from the January 2011 issue of Auto Enthusiast Magazine.

Stop Losing Your Cool! - A/C In Your Muscle Car


Our subject 1971 Mustang had been plagued with air conditioning problems for years. When it was working, it might last two months [after being worked on] … or it might last one week. To add insult to injury, the compressor would occasionally bind up and cause the A/C belt to squeal.

Service work had been performed at various garages, including numerous recharges, a new expansion valve and removing the compressor to verify it had not been overfilled with oil. The owner had disconnected the compressor energizing wire because he was fed up that he could never flip the A/C dash switch and be guaranteed it would perform properly.

A typical A/C system works when Freon leaves the compressor through the high-pressure [discharge] side as a high-pressure gas. It enters the condenser and receiver dryer, where it transforms into a high-pressure liquid. The high-pressure liquid then travels through the A/C hose, where it enters the expansion valve [remember, as a high-pressure liquid]. From the expansion valve, it goes into the evaporator, where it exits the evaporator as a low-pressure gas. The low-pressure gas then returns to the compressor, where the cycle starts all over again. Simple, huh?

Our game plan on this car was to sort out the problems and, because the price of R-12 is through the roof or not available, convert the car to R-134A.

Tools needed for the project were safety glasses, basic handtools, a set of A/C gauges and an A/C vacuum pump. When we acquired this vehicle, it had no Freon in the system, so it was not necessary to evacuate the system. If the car would have had any residual R-12 Freon remaining, it would have been necessary to have that Freon evacuated and reclaimed by a certified service center [it is illegal to vent R-12 Freon into the atmosphere, according to the EPA].

We started our diagnosis of the problems by installing the conversion R-134A service port to the low [suction] side of the compressor and opening the valve located on the hose connection. From there, we started the engine, energized the compressor and allowed the compressor to pull in 22 ounces of Freon for initial testing [an A/C system can’t be tested for low- and high-side gauge readings if it’s empty]. Within minutes, the needle on the low-side gauge started going toward the negative side of the dial. A properly functioning system would have gone opposite of that, heading toward approximately 25 inches of vacuum. This action was an indication of a severe restriction within the system … but where?

Previous work had included a new expansion valve, so we would rule that out [for now]. The next most likely culprit was either the condenser or the receiver dryer, both located in front of the radiator. In order to access the condenser/dryer, our first step was to remove the hood latch assembly and its support brackets. With those out of the way and our newly installed R-134A reclaimed and stored, we proceeded to disconnect the A/C hose attached to the condenser and the remaining hose that was connected to the receiver dryer. With the two lines disconnected, we used compressed air to blow into the top condenser opening to check airflow which should be exiting the open dryer connection. Bingo! There was no air exiting the open dryer connection, verifying a definite restriction in one, or both, of these units. Note: never replace an A/C condenser without installing a new receiver dryer.

We knew replacing these two parts was our starting point in this project, so our next order of business was to order our new condenser and receiver dryer. While the parts were in transit, we removed the old unit [as an assembly] by extracting the four retaining bolts and lifting the condenser/dryer from the vehicle.

Our parts arrived in short order with necessary new seals and retaining screws. With our new parts assembled, a reverse of removal brought us to the point of evacuating the system and recharging it again with R-134A.

When an A/C system is evacuated with a vacuum pump, that system can be checked for possible leaks. A vacuum pump will also remove contaminants and air from the system, plus draw a negative reading on the low-side gauge to approximately 29 inches of vacuum. When our low-side gauge reached 29 inches [give or take an inch or so], all gauge valves were closed, the vacuum pump shut off and the gauge monitored for possible leakdown. A sealed system will maintain the 29 inches of vacuum for 30 minutes. Our system held the vacuum for the required time, so recharging with the required 1¾ pounds of R-134A was the next step. After a recharge and road test to verify cool air was coming out of the vents, we shut the compressor down along with the engine and performed our last inspection.

With a mixture of dishwashing liquid and water in a spray bottle, we squirted the mixture on all hose connections and watched for bubbles. None appeared, so our Mustang A/C system was being cool … and good to go.



1 After installing the R-134A service port and connecting the low-side gauge line, a ¼-inch A/C wrench was used to open the factory service valve. These valves turn clockwise to open and counterclockwise to close.

2 The hood latch assembly was the first to be removed for accessing the condenser and receiver dryer.

3 Removing the two hood latch braces required extracting four screws through the front of the grille with a long Phillips screwdriver and removing two 3/8-inch bolts under the bumper.

4 With the retaining screws and bolts removed, our hood latch braces were simply lifted up and out.

5 Care must be taken when removing or installing A/C lines connected to any part of the system.

6 It was also necessary to remove the bracket securing the A/C lines to the front clip panel.

7 The four retaining screws holding the condenser and dryer were extracted, thus allowing for easy up-and-out of the assembly.

8 After dissecting the old receiver/dryer, it was pretty obvious this A/C system had serious problems.

9 When recharging any A/C system, gauges such as these should be used to ensure refill accuracy.

10 Conversion kits, such as this one found at the local auto parts store, are readily available for bringing an older vehicle into the 21st century using R-134A Freon. This kit retailed for $44.99.

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