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Any time an A/C job like this comes in, I want to know a few things before I get very far into the diagnostic process. I start my quest for information with things like proper blower operation, proper engine cooling fan operation and the amount of charge in the system.
I reached in the open driver's window and started the engine. With the blower on high and the system on max cooling, the air velocity from the dash vents was a little less than expected. I then opened the hood and took a look at the engine cooling fan. With the engine at 2,000 rpm, I could hear the fan working hard, and I also could feel the good volume of hot air coming from the fan.
The next step was to run my hand over the evaporator discharge line to verify the system was full of refrigerant. All of these initial checks proved out good, except the air flow from the dash vents. Two possibilities came to mind: either a blower fan problem or a restriction in the evaporator.
Before I pulled the blower fan or the evaporator case out, I thought it would be a good idea to hook up the gauges to see if I could determine the real cause of this problem.
When I did my visual, I did not notice any oil spots on any of the hoses or at any of the quick coupler joints, but I did notice a new compressor and accumulator had been installed on the vehicle. I wondered if someone had replaced the compressor for this complaint, but it didn't fix the problem? A few minutes with the gauges and a thermometer in the center vent should get the information that I'm looking for. With the gauges hooked to the high and low side charging ports, I placed thermometer sensors in the center vent and at the front of the radiator.
With the engine at idle, I found the compressor clutch would cycle on and off much like a system that was low on refrigerant. The vent temperature was 74°F with an ambient temperature of 99°F. The low side gauge would drop to 22 psi and the compressor clutch would open. The high side gauge was also moving between 50 and 160 psi as the compressor clutch was cycling. This sure looked like the A/C system was under charged, but my hands on the ice cold evap discharge told me otherwise.
We all know that some parts of the A/C system are supposed to be hot and some parts are supposed to be cold. By running your hand across the condenser, you can detect any hot or cold spots.
A cold spot on a condenser is telling you there is little or no refrigerant flow through the condenser in that spot. If you feel a refrigerant line that is supposed to be hot and you feel a cool spot in the line, you have found a restriction in that line. If you feel a line that is supposed to be cold and it is not nice and cold, then there is a problem with the refrigerant flow in the system. This system was hot and cold in all of the right places.
An R134A refrigerant system will perform well within a window of ±10 percent. I went to the service information and found this system is designed to hold 30 ounces of refrigerant. With this information, I knew this system should work well with a charge of 27 to 33 ounces.
Because the gauge pressure gave me the indication the system was under charged, I gave it another 4 ounces. With the extra charge, the vent temperature moved from 74 to 76°F. It sure looks like it is overcharged.
Before I left for lunch, I switched the refrigerant recycler over to recover. When I returned, the recycler had removed the entire refrigerant charge from the system, and the scale showed that 50 ounces of refrigerant had been removed. With a 20 ounce overcharge, no wonder it wasn't cooling. Because the system was now empty, I gave it a recharge of 30 ounces of virgin gas.
With all windows open, the controls set for maximum cooling and the engine running at 1,500 RPM, the gauge pressures and vent thermometer showed the same readings as the first test. Low side pulling down to 22 psi, the compressor clutch cycling, a maximum high side pressure of 110 psi, and a vent temperature of 74°F.
In the case of this Ford Ranger, the low side gauge told me that the evaporator temperature is too cold. The high side pressure gauge is too low for the ambient temperature, That told me that there is not enough heat in the condenser, caused by the evaporator not pulling heat from the passenger compartment. This sure looked to me like something was restricting the airflow through the evaporator. If this vehicle had a cabin air filter, now would be a great time to see if it were causing the restriction. I did check, but this vehicle did not come equipped with a cabin air filter.
The 2001 Ranger evaporator case sits inside the engine compartment, so no dash removal is needed for evaporator removal. The engine air cleaner, the coolant recovery tank and the cruise control module are the only things that need to be removed to gain access to the evaporator case. Once these parts are removed the evaporator case is easy to access.
There are three nuts to remove from the engine side of the evaporator case and one nut to remove from the passenger compartment side, two heater hoses and two refrigerant lines, then the evaporator case can be lifted out of the vehicle. When the evaporator core was removed from the case, I found that most of the air flow was being blocked by a coating of damp brown dirt. This blockage explains the low pressure readings on both the high and low side gauges and the low air flow from the dash vents.
Low air flow through the evaporator causes low heat transfer and the evaporator to get too cold. This low temperature is reflected in the gauge pressure. Because the evaporator is not able to remove heat from the passenger cabin, the condenser will also have a lack of heat. The gauge pressures were pointing me straight to the problem, low air flow through the evaporator.
The evaporator case was installed back in the Ranger. When I got around to putting the spring lock fittings together, I had a flashback a few years to the first Ford vehicle I worked on with these fittings. At times, this type of fitting can get a little nasty inside and not seal very well.
If you are working on A/C systems and expecting great results, using the proper tools is a must. A set of cleaning brushes is one of the must have tools for this job. The brushes are made with brass bristles and fit snugly inside of the fitting. A light application of carburetor cleaner to the brush and a few turns of the brush will remove any dirt and light rust inside of the fitting. A new set of the proper size O-ring seals and a nice snug fit of a plastic reinforcement clamp and the fitting will seal. This added touch will ensure that your customer will not be back again because the system is leaking.
I hooked up the vacuum pump and the system pulled to a deep vacuum, the proper amount of oil added and the system charged with new refrigerant, then performance tested. With the engine idling at 1,200 rpm and the blower on high speed, the vent temperature came down to 42°F with the low side pressure reading 28 psi and the high side pressure reading 185.
After any A/C repair like this I always like to park the vehicle out in the sun, let it heat soak, then start the engine and see how long it takes to pull the passenger compartment temperature down to 75°F. It is also a good time to go over the A/C connections again with either a leak detection light or an electronic leak detector as a final test.
Albin Moore spent 21 years in logging before opening in 1992 a shop that specializes in drivability problem analysis. He is an ASE CMAT L1 technician with 40 years of analyzing and fixing mechanical and electrical problems.
