A/C Liquid Line Frozen

Looks like your gonna have to throw the gauges on it and see what kind of readings you get. If the line is getting that cold that quick, I want to say there is a blockage of some sort.

GT

Since you are not familiar with how A/C works, here some background theory:

The condenser is up front of the radiator, and it is supposed to condense the hot gas from the compressor into a hot liquid. The hot liquid goes to the expansion valve located in the last 6" or so of tubing next to the firewall. The expansion valve lets the hot liquid expand and become a cold gas, the cold gas goes to the evaporator inside the car where the fan blows on the evaporator exterior. The heat transfer from the air inside the car to the cold gas inside the evaporator causes the A/C to blow cold air. The now cool gas goes to the compressor where it gets compressed again into a hot gas and the process starts all over again. Keep in mind that this is a closed system, and the gas inside the A/C doesn't get out unless there is a leak, which is where you are at.

Here's where the problem gets sticky. All the original fox body Mustangs were made to use R12 refrigerant. R12 is no longer available unless you have an EPA 609 license. That means the system needs to be converted to use R134. Putting R134 on top of R12 without doing a proper conversion will cause compressor failure and metal from the compressor will circulate throughout the system. When this happens, it requires an extensive and expensive flush of the A/C system to get all the metal and other contaminants out. Skip doing the flush and clean thing and the new compressor will quickly fail.

When a R134 conversion is done, the installer is supposed to replace the service fittings with R134 style quick connector couplings.






Then he places a R134 conversion sticker on the car. The typical sticker looks like this, yours may be different.



They are also supposed to replace all the O rings with R134 compatible O rings. The R134 gas molecule is smaller than the R12 molecule, so R12 O rings will be prone to leakage.

See R134a Conversion for R134a Conversion & recharge help

If the gas leaks out, usually it is because one of the O ring seals is bad. High quality R134 conversion is supposed to include new green O rings for all the joints and couplings. When you open the system to replace the O rings, all of the refrigerant must be removed and recovered and the system vacuumed down prior to recharging.

R134 recharge kits with refrigerant/leak detector dye can are available at most auto parts stores. Some of the R134 refrigerant refills have a leak stop in them. BUT beware! The stop leak can block the expansion valve, causing system failure. The refrigerant/dye recharge kits are popular because the green dye makes a very visible indicator where the leaks is. Some of the recharge kits include a pressure gauge so you have some idea of how much refrigerant is in the system while it is running.

The hottest part of your A/C lines will be downstream of the compressor between it and the condenser. The liquid line will be warm, but cooler than that. Tubing routing, missing insulation, and engine heat can affect that. Immediately before your evaporator, the freon supply goes thru an expansion device (either valve or orfice as the case may be), that's when it gets super cold. If there is not enough airflow over the evaporator, it will freeze up in a hurry.

When you turned the A/C on and it started freezing, was the blower motor running? The system is counting on quite a bit of hot air blowing across the evaporator coil to absorb heat from the air, which in turn heats the coils and keeps them from freezing.

You already know you have a leak somewhere. If you've already double checked your o-ring connections, it may be inside the evaporator coil, inside the heater box. In an automotive environment, the o-rings are definitely the place to look first; look for an oily residue, its a dead giveaway.

Hope this helps...

Air conditioning electrical troubleshooting 87-93 Mustangs.

Diagrams courtesy of Tmoss & Stang&2birds


Check out TMoss's diagram I posted. Anytime the clutch is energized, the black/yellow clutch power wire should show 12 volts or whatever the battery voltage is measured at the battery.

Make sure the black ground wire is good, and that it connects to a clean bare metal place on the engine. Measure the voltage between the black/yellow wire and the battery ground cable. Good 12 volts, then you have a bad ground. The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges

No 12 volts on the black/yellow wire, check voltage at the pink/blue wire on the WOT relay: it should be 12 volts. The WOT relay is located under the Mass air meter on the passenger side.

Good 12 volts on the pink/blue wire on the WOT relay, ground the orange/lt blue wire on the WOT relay. Recheck for 12 volts on black/yellow wire. No 12 volts on the black/yellow wire, recheck your ground for the orange/lt blue wire. If it is good, replace the WOT relay.

No 12 volts on the pink/blue wire on the WOT relay, check out the low pressure cutout switch. Look for 12 volts on the green/purple wire.

No 12 volts on the green/purple wire, the A/C control switch is bad or the power to the switch is bad.


The next step is valid only if you are sure there is sufficient refrigerant change to make the system operate. The low pressure switch is supposed to shut off the compressor if the refrigerant charge is low. It does this to protect the compressor, since the refrigerant helps to circulate the oil that lubricates the compressor.

If there is good 12 volts at the green/purple wire, measure the voltage drop across the low pressure cutout switch. With the switch connected, probe the back of the switch connector. Use a pair of paper clips or safety pins to measure the voltage between the green/purple wire & pink/blue wire. Do not connect the voltmeter to ground, just the two wires. This measures the voltage drop across the low pressure cutout switch. You should see less than .75 volts. Less voltage drop is always good, but more voltage drop is bad. More than .75 volts, replace the low pressure cutout switch. It unscrews without draining the system or causing more than a short PIFF of gas escaping. The local auto parts store should have a replacement switch. Inspect the low pressure cutout switch wiring harness contacts before replacing the switch. A replacement pigtail is also available at the local auto parts store.



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
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