REFRIGERATION COMPRESSOR FAILURES ON SMALL UNITS/ MOBILE AIRCONDITIONING SYSTEMS

Compressors have the highest rate of failure of any REEFER component. Yet compressors very seldom fail on their own and it is imperative that the cause of failure be properly diagnosed and corrected when replacing the compressor. If this is not done, the replacement compressor will also fail in a very short time.

A compressor is an engine. A lubrication or a “coolant” issues caused engine failure in maximum number of cases.

COOLANT FAILURE

This means lack of heat removal from the condenser resulting in a high head pressure. On very hot days this means a high side reading well over 300PSI( more than 20.7 bar).

A.   Too much refrigerant. (Overcharge)

B.   A dirty bug screen or debris blocking the condenser.

C.  A clogged radiator/cooling system.

D.  A defective fan clutch or switch that activates the fan clutch.(for mobile trucks where AC system is driven and clutch controlled to engage/disengage)

E.   A pinched tube in the condenser – reducing the condenser output- caused by handling damage (if retrofitted or replaced).

F.   Improperly operating shutters.(if there is a shutter opening during operation)

G.  Contaminated refrigerant.(improper method of charging with moisture ingress inside or wrong gas added)

8. Excessive air content (non-condensables gas) in system.(due to improper method of charging/ replacement of gas) .Air  enters the system through loose fittings, deteriorated o-rings, and shrader ports. Even though the air conditioner has refrigerant in it, which means the pressure in the inside of the system is greater than the outside, air permeates (or goes through) the rubber hoses of the a/c system .

LUBRICATION FAILURE

Compressor needs to be lubricated by a special refrigerant compatible oil. The oil is carried through the a/c system by the refrigerant. The oil will not circulate without refrigerant. Therefore, compressor failure due to a lubrication problem is caused by:

A.   Loss of refrigerant which means no carrier of the oil and no lubrication for the compressor.

B.   A blockage in the system. This will keep oil from returning to the compressor and will normally show up as too low a reading on the low pressure gauge. "Too Low" a reading means 0-10 PSI(0-0.8 bar) or a vacuum. The blockage may be in the form of:

1.   A clogged filter drier/expansion valve/orifice tube.

2.   Moisture in the system , which is manifested like-If the driver says the air conditioner works okay for a short time then starts blowing hot air and that if he turns it off for a while and then turns it on it works again for a short time, the odds are that there is moisture in the system.

3.   Moisture will lead to formation of Hydrofluoric acid and other acids in interaction with lubricating oils and refrigerant – thus reducing lubricity and failure of compressors.

Note :A defective thermostat or clutch cycling switch will cause the same symptoms like moisture, however a watery smell will also be present.

4.    mechanically closed expansion valve. Some types may be removed and blown through (with mouth) to check.

Although these parts can be checked and cleaned, the service industry, as a general rule, will replace them.

Airconditioning system needs to be treated as a single unit – even though the failure can be with a single component , the system has to be commissioned as a whole, when installing the component in order to avoid failures in other components. The important thing is that at some point, usually between one and three years of installation, the drier is no longer able to absorb the moisture. This moisture will mix and react with the refrigerant to form various acids. The acid will “eat” away at the metal surfaces and rubber hose, flaking off bits of material that will collect at the filter drier/accumulator screen, expansion valve, orifice tube, and the compressor. This debris will slow or stop the flow of oil from returning to the compressor and will cause compressor failure.

Evaporators, especially aluminum units, commonly fail because of leaks that develop at the bottom of the core. Acids that collect at the bottom of the evaporator and “eat” through the very thin aluminum cause these leaks. Condensers, including those made of copper, steel or aluminum also develop leaks from acid eating through from the inside .

Acid will cause small “pinhole” leaks to develop in the condenser coil and the evaporator coil. Flaked off debris and sludge will flow to the bottom tubes of the condenser causing both restrictions and a concentrated accumulation of acid to eat at the coil. Sludge and debris at the bottom of the evaporator coil will not normally cause a restriction but will eventually cause reduced cooling efficiency.

The procedures to be adopted while commissioning a system can be given under the following heads

1.  Physical check of components with leak test

2.  Flushing the system

3.  Installing new components

4.  Refrigerant charging procedure .

1.Physical check of components

1.   Ensure that that the fan clutch, or electric fan assembly, if there is one or more on the vehicle, is working properly. If not it must be replaced or repaired. Check the switches and controls for the fan and/or shutters.

2.   Clean the bug screen (if there is one). Check for debris in the radiator and the condenser fins and/or loose fins.

3.   Check for good flow of coolant through the radiator.(air flow)

4.   Check if there is a loss of refrigerant- pressure test/ vacuum test- in case the system is intact – before any disassembly.

5.    If the system contains refrigerant it must be recovered by an approved Recovery or Recovery/Recycling System (vacuum unit with a recovery cylinder) .

6.   Disconnect the liquid line (the smallest diameter hose or line) at the expansion valve or orifice tube and closely examine for contamination. If any contamination at all is found, whether it is in the form of sludge, powder or grit, rust or metal flake, aluminum oxide or metal shavings from the compressor, the entire system must be flushed

           2.Flushing the System

 1.   Purge air conditioning system. Use a recovery system to collect any gas before disassembly.

  Components not to be flushed – and have to be removed prior flushing.

-     Compressors

-     Valves

-     Orifice plates

-         Accumulators and iquid driers

3.   Remove and discard accumulator or filter-drier.

 4.   Disconnect discharge hose/ tube at compressor.

 5.   Disconnect suction hose at compressor.

 6.   Disconnect suction hose at evaporator. (If this is a filter-drier system)

7.   If system has an orifice tube, remove and discard. (Orifice tube normally is located inside inlet end of evaporator)

8.   Consult MSDS sheet and label of flush solvent for precautionary measures. Pour 1 to 2 pints of flush solvent through top of flush gun. Re-attach top nut with your quick disconnect.

9.  To avoid spraying of oil, flush solvent, and other debris, attach a piece of hose to end of component being flushed. Place opposite end of venting hose in large can and fill with rags or other absorbent material.

12.  Attach your compressed air hose to quick disconnect. Flushing will work efficiently from air/ nitrogen pressure of 7 bar.

13.  First flush from end of discharge hose at compressor, through hose, condenser and liquid line to point either where the filter drier was discarded or where liquid line was disconnected at evaporator.

14.  Flush remaining liquid line hose if system has filter drier between condenser and evaporator.

 15.  Flush suction hose between evaporator or accumulator and compressor.

16.  If system has an expansion valve, remove and clean. Reinstall or replace.

17.  Flush evaporator.

18.  If compressor is not being replaced, the oil should be drained and replaced with clean refrigeration oil. If a replacement is being installed, check for correct amount of oil already in compressor.

20.  Wait approximately 20 minutes for flush solvent to evaporate. Evaporation rate of solvent is dependent upon the type and brand of flush solvent used and the ambient temperature. Slow evaporating solvents may be “blown out” of system using dry, clean compressed air/ nitrogen.

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3.Installation of new components

           1.The proper amount of oil must be replaced in the system.

a.   Drain the oil from the replacement compressor (new or remanufactured).

b.   Install the following amount of oil in the compressor:

3.   CCl/York and Tecumseh 2 cyl. compressors - in vertical position oil should stand approximately 1 inch.

4.   Frigidaire (GM.) A-6 - fill with oil so that when compressor is held in operating position - oil will just start to drip out of the loosened oil filler plug.

5.   GM DA6/R4/HR6HE; FORD FS6, FX 15 (FS 10); DIESEL KIKJ (ZEXEL, SELTEC/TAMA) and SANDEN - install 5 ounces of oil.

           2.Install the replacement compressor.

           3.For added protection, install an in-line filter between the filter-drier and the expansion valve or orifice tube.

 4.Attach hoses, installing the filter drier (or accumulator) last.

           5..Add the following additional amounts of oil:

Compressor Type	System Completely Flushed w/o Bunk Unit	Evaporator Not Flushed	System Completely Flushed with Bunk unit
CCI/YORK, TECUMSEH*	3 ounces	2 ounces	5 ounces
FRIGIDAIRE* (GM)A-6 GM DA6/R4/HR6/HR6HE* FORDFS-6/FX15(FS10)*	3 ounces	2 ounces	5 ounces
DIESEL KIKI (ZEXEL, TAMA)* SANDEN	3 ounces	2 ounces	5     ounces

               Additional amount of oil can be only poured into the discharge hose- not in suction line.

      6.The system should now be completely assembled, with the proper amount of oil and new drier, new or cleaned expansion valve, and new o-rings if required.

7. To prevent the shaft seal of the replacement compressor from leaking or blowing out – ensure  that after installing the compressor on the vehicle(for mobile units), but before installing the belt, turn compressor clutch by hand 10- 12 times. This brings oil up to the seal and lubricates it. Note the GM DA6/HR6/HR6HE compressor cannot be turned by hand. Turn it with a socket and ratchet by hand. DO NOT USE AN IMPACT.

7.   Your service gauge set should be hooked up. Add about one quarter pound refrigerant. Watch your gauges. They should equalize. The pressure from the refrigerant will help "seat" the lubricated seal.

8.   Purge system using your refrigerant recovery/recycling equipment. Follow your machine's instructions to insure complete recovery of refrigerant. Evacuate system for 30 sec. to a minute so that low side gauge reads a vacuum. Close valves on gauge set and turn off vacuum pump. If vacuum bleeds off, find and repair leak. If not, or after repair, proceed to next step.

9.   Evacuate the system for a minimum of 45 minutes. Although the system is clean and free of acidic oil, 45 minutes is necessary to insure a moisture free system. .

10.     Continue to charge the refrigerant once vacuum test is satisfactory.

COMPRESSOR REPLACEMENT REQUIRES THE INSTALLATION OF A NEW RECEIVER-DRIER/ACCUMULATOR AND FLUSHING THE SYSTEM! 

Charging up an HVAC system running short of refrigerant.

Rule of thumb: Superheat at outlet of evaporator : 10 deg Farenheit (difference between bubble and dew point temp for non azeotropic mixtures

1. Connect all the hose 1, 2 and 3 with the HVAC kit.
2. Purge air from the hose from 2 to 1 by tightening it at point C, valve A open, valve B closed and connection to the charging cylinder slightly open for air purging, later close after purging.
3. Likewise, air purge the high-pressure side hose 3.
4. Keeping the HVAC system running we will open the charging cylinder gas valve, valve B closed and open the valve A, allowing the refrigerant charge into the system
5. Start charging the gas refrigerant to the low-pressure side of the HVAC system at connection C by opening the valve A and the refrigerant valve until the vacuum comes to zero.
6. Now start the compressor as the suction pressure goes above zero.
7. After about 30 – 40 seconds of charging close the valve A and check the suction gauge pressure for a rise in pressure.
8. Keep monitoring the degree of superheat by the temperature calibrator to ensure liquid refrigerant is not entering into compressor suction also we can calculate how much charge present in the system by the pressure chart.
9. If the superheat temperature is high, then it means the system is running low in refrigerant whereas lower superheat temperature than the desired value means the system has overcharged.
10. Repeat the procedure 10 to 11 until the suction pressure reaches to 60 psi (as per maker) this avoids the risk of overcharging of the system also keep measuring the refrigerant by the weighing scale.
11. Once the refrigerant has charged, disconnect all the hoses and secure everything.

Liquid refrigerant charging procedure for an air conditioner

1. Evacuate the system by pumping down the refrigerant into a recovery bottle using a vacuum pump.
2. Connect the liquid and gas line hose and purge it.
3. Connect the charging hose to the red connection of the charging cylinder for a liquid charge, and if only one connection provided, then we need to invert the cylinder.
4. Attach the temperature probe at the correct location near the sensing bulb to sense the degree of superheat and subcooling at the condenser outlet.
5. Allow the liquid refrigerant to flow by opening the valve A and keeping the valve B closed.
6. Since the system has a vacuum, the liquid refrigerant itself enters the system and move towards the evaporator and condenser until the pressure comes down to the charging cylinder pressure.
7. Start the system, the liquid refrigerant gets equally divided between the evaporator and the condenser, and no danger of liquid flooding exists in the compressor.
8. As the refrigerant leaves the charging cylinder, the charging cylinder pressure decreases, so to maintain the flow create a negative pressure by partially closing the receiver outlet throttle valve and allow the refrigerant to flow from the cylinder.
9. In a refrigeration system, receiver outlet is provided with a “king valve” used for liquid charging also known as a throttle valve and can trap the entire system refrigerant inside receiver.
10. This way liquid refrigerant gets admitted safely, but since the throttle valve reduces the pressure across the expansion valve, the system doesn’t run normally.
11. In between close the refrigerant charging valve A and open the throttle valve fully and check the temperature and pressure readings.
12. When fully charged the sight glass get’s clear also weigh the charging cylinder to know how much charge required as per maker for a full recharge.