Hissing Expansion Valve

The most common expansion valve failure is due to valve charge head leaks. System contaminants lodged in the valve inlet orifice may also affect valve metering and flow capabilities.
Suspected metering inconsistencies many times have distinct characteristics. Starving Expansion Valve: Frost will form on the inlet of evaporator causing a flooding the Expansion Valve: Causing a hissing sound at valve upon system shutdown.

Air Conditioning Fitting Torque Specs

Flare Connections
5/8” thread #6 18-20 Ft/Lbs
3/4" thread #8 36-39 Ft/Lbs
7/8” thread #10 52-57 Ft/Lbs
11/16” thread #12 71-79 Ft/Lbs

O-Ring Connections
5/8” thread #6 11-13 Ft/Lbs
3/4" thread #8 15-20 Ft/Lbs
7/8” thread #10 21-27 Ft/Lbs
11/16” thread #12 28-33 Ft/Lbs

These specifications are important to avoid leaks at your air conditioning fitting connections and to avoid o-ring damage.

Compressor Clutch Slippage

Clutch slippage is a common cause for clutch and or compressor failure. The heat created when a clutch slips can damage the pulley bearing and weaken the compressor shaft seal. During any service work to the a/c system always check voltage to the clutch coil and air gap between the hub and pulley to prevent slippage.

Definition of Superheat

Temperature of a Vapor above the boiling temperature of its liquid, at a specified pressure.

EXAMPLE: At 28 psig R-134A boils at 0C. If the refrigerant temperature is measured at 4.4C it is superheated by 4.4C, above the temperature of boiling. This insures that all liquid has turned to vapor.

To protect the compressor you must make sure that no liquid is returned to it. Compressors are "Vapor Pumps Only". The refrigerant absorbs heat from the air blowing over the evaporator and releases heat through the condenser (when a system is properly balanced and functioning well).

Compressor Failure

Should a system experience an internal compressor failure, it may not be possible to completely clean the system of the debris from the failure. Since heat exchangers (evaporator/condenser) have very small multiple internal passages and internal baffles, flushing may not clean all passes returning the heat exchanger to its expected level of performance. Replacement of an orifice tube or replacing the expansion valve must be done to assure maximum performance. Replacement of the accumulator or receiver dryer is necessary when an internal compressor failure has occurred. Flushing of flexible hoses and refrigerant lines maybe be required as well as the installation of auxiliary filters of compressor screens. Hose assemblies having inline mufflers should be replaced, since flushing may not remove all the debris from the failure. Liquid lines that contain permanent orifice tubes must be replaced. Installation of non-restrictive in-line filters minimizes the chances of the re-circulation of any foreign material remaining in the system. Movement of debris can reverse flow from the system high side to low side when the system is shut off and equalizes, resulting in the contamination of low side components (the accumulator and evaporator).

Alternator Overcharging

Most people believe that the cause of over charging is from stuck regulators, as this can be the problem, more than likely if the tractor has had more than one failure, it is time to look elsewhere.

Bad or corroded battery cables, bad ground, a worn spot in wiring, and a dead cell in the battery, can be causes of over charging. The alternator can interpret these conditions as low voltage in the battery, and keep charging. When the alternator keeps charging it can cause the battery to loose water, and when the plates are exposed, they can arc, and the resulting spark can explode the battery.

Receiver Drier Operation

Did you know that...
The primary function of the receiver drier is to remove moisture from the HVAC system? Under normal operating conditions the drier canister should be warm to the touch. The presence of frost on the canister indicates an internal restriction in the drier itself or downstream in the condenser.

Expansion Valve Replacement

The most common block valve failure is due to the loss of the gas charge inside the power element head. Plugged expansion valves cannot be flushed out and must be replaced. When replacing a capillary type expansion valve make sure the capillary coil or bulb is properly attached to the outlet side of the evaporator line, the two mating surfaces need to be thoroughly cleaned to assure good metal to metal contact and well insulated with Prestite insulation tape part # 881721.

Expansion Valve Troubleshooting

How can I tell if the expansion valve is bad?

This has to be our least favorite item to diagnose. We've had expansion valves quit working while on the road and show no signs of problem back in the shop. What's worse, an expansion valve can stick closed, stick open, or hang somewhere in between. Of all the bad expansion valves seen over the years, I think those that stick closed are most common. Those are the easy ones. Gauges will show very low suction side pressure along with lower than normal high side pressure. The low side may even draw into a vacuum. That's a big clue. Those that appear to be stuck closed may have inlet screens clogged with ground up desiccant particles from the failed drier. This will look like beach sand packed into the inlet. It's common for a defective expansion valve to stick in the closed position, however, the expansion valve can also stick open. This is indicated by higher than normal low side pressure, and slightly higher than normal high side pressure. To some, this might appear as a weak compressor or slightly overcharged system.

Proper Charging Procedures

Should I test with doors open or closed, high idle, blower on high or low?

We should measure high and low side pressure at stable engine speeds. This can be done at engine speeds just slightly above idle. 1,200 to 1,500 RPM is most often recommended. On front wheel drive cars, never rev the engine or hold the engine at high RPM while charging or checking pressures. This can create dangerous high pressure. This is because electric condenser fans are fixed in speed, and will not compensate for high engine RPM. The same holds true on rear wheel drive cars with engine driven fans. A defective fan clutch could cause pressures to reach dangerous levels at higher engine RPM. We like to test with the system in MAX position on high blower with doors closed. Windows can be open. MAX (re-circulate) mode is preferred since we'll need to have the hood up while charging and testing. In fresh air mode, hot engine heat can be drawn into the fresh air cowl under the wiper blades. Same reason we would like to test with doors closed. We would like to keep engine and exhaust heat from causing abnormal heat load on the evaporator. We're not bothered by having the windows down, since this helps create a typical and stable heat load. And it's easy to reach in and feel how cold the vent temps are getting. Testing should be done with blower speed on high. Low blower speed will reduce heat load on the evaporator to the point where compressor cycling can occur. We want nice stable conditions when testing. When needed, low blower speed can be used to force low side pressure down during testing and adjustment of compressor cut-out pressure.

High Side Pressure

With R12 systems, high side pressure is usually 1.8 to 2.1 times ambient temperature. That means on an 80 degree day, with moderate humidity, we would expect to see between 144 to 168 PSI on the high side. On hot humid days (with R12), you could say ambient temperature plus 100 PSI., and be pretty close. With R134a it's common to see high side pressure between 2.2 and 2.5 times ambient temperature. On that same 80 degree day we would see between 176 and 200 PSI on the high side of an R134a system. The system operates in a specific range based on outside ambient temperature. High side pressure has a broad range relative to temperature because of heat load on the evaporator, humidity, airflow across the condenser, and engine speed.

Fittings and Corrosion

Did you know that the process that causes fittings to seize up is called electrolysis?

To help prevent this apply mineral oil to the threads of the fittings before tightening. Also apply to the o-rings to help them seat properly. This is very common with the use of steel fittings installed on aluminum such as Sanden compressors and aluminum condensers. When steel fittings seize to the aluminum compressor usually the threads pull right off the compressors resulting in the rear head on the compressor to be replaced. Aluminum fittings seized onto connections often result in just the threads from the aluminum fitting separating this can be repaired using a thread chaser Hy-Capacity part # 8819TCK500.

Oil and Compressors

Remember to always check your newly purchased compressor for oil. Now many new and rebuilt compressors come without oil. Inadequate or excess oil in the system will cause loss of performance and compressor damage as well as other component damage. Seltec (HD Sanden Style) remains the only compressor manufacturer to guarantee it�s compressors to be loaded or full of oil.

Compressor lock up

Air conditioning compressors and internal combustion engines share many similarities. Both seize up or lock up for a reason. 1. The most common cause of compressor lock up is the use of non-compatible oils and refrigerants. Most re-man compressors come with Mineral oil in them which is for R-12 refrigerant. Introducing 134A or any other refrigerant not compatible with Mineral oil will result in the almost immediate failure of the compressor, often times this fatal error by the installer does not even make the trip home. 2. The next most common cause of compressor lock up is overcharging. When a system is overcharged to the point the suction fitting on the compressor frosts up, liquid refrigerant with the capability to still cool has made its way to the compressor. This is sometimes called pooling or flooding the compressor, when this liquid refrigerant is pulled into the compressor it may seize, throw the belt or may make strange noises? Failure to remove the excess refrigerant will surely result in a compressor failure. 3. Another common cause is high head pressure, this to can stop the compressor from turning making the operator think they have seized up. In this instance however the compressor will work fine until the pressure spikes again. This can be due to many things including the over charging of the system, restrictions in the system, non-functioning pressure switches, even a condenser that is plugged up with debris or a condenser that has lost it’s ability to efficiently transfer heat can be a cause. 4. The last one can be a tough one! In the event a compressor runs for quite a while and performs great and all of the sudden seizes up, be a little skeptical! Remember the engine comparison, what kills an engine will kill a compressor! Contamination or lack of lube. Debris from upstream in the system can find their way into the compressor causing extensive damage. Usually the depletion of the oil in the system is the cause of this scenario. Every farmer knows how to add a can of refrigerant, they usually forget to add oil to compensate for the oil that had leaked out over the winter with their Freon. By the time they add their 2nd can of Freon the system will be substantially low on oil and may even be depleted if the installer did not add the appropriate amount at installation.

Replacing a one wire clutch with a two wire

Sanden compressors come in two types the SD series which was set up for R-12 that had one wire coming out of the clutch coil and the SD7H series set up for 134A which has two wires coming out of the clutch coil. Often times the tractor or piece of equipment was R-12 from the factory but the replacement part supplied by us or the OEM may be the 134A or later version resulting in the customer having one hot wire to connect to a compressor that now has two wires. The clutch coils with two wires can be fed from either direction simply connect the hot wire to either of the coil wires and connect the other to the ground preferably a compressor mounting bolt.

Drier replacement

When either installing a new a/c system or doing a service job always make the drier the last component replaced before evacuation and recharge. The desiccant in the drier absorbs moisture and will decrease performance and create a problem to the system at a later date. Moisture and refrigerant when combined creates an acid and will damage the internal parts of the a/c system.

Reed Valve Troubleshooting

Poor system performance could be faulty reed valves. A hissing sound from the compressor immediately after shutdown indicates high side to low side pressure leakage. To check this, attach manifold gauges and turn compressor on. Readings showing lower than normal discharge pressures and high suction pressures or a rapid stabilization of gauge readings shortly after shutdown indicate leaking reed valves or head gasket.

PAG and Ester Oil Care

When working with either PAG or Ester oils always be sure to keep the container capped when not in use. The chemical makeup of these types of oils will absorb moisture and can create a problem in the a/c system later.

Charging Precaution for Liquid Refrigerant

Inverting the can and charging with liquid refrigerant while the compressor is running will wash the oil off the axial plate, piston balls, piston shoes and thrust bearings leading to a premature failure of the compressor.

Replacing Compressor Clutch Snap Ring

When replacing the clutch assembly always make sure to re-install the snap rings properly. Snap rings have two sides, one is flat and the other beveled. The beveled side should always go to the outside to ensure proper fit.

Why clutches fail

Did you know that Most clutches fail due to low voltage which causes them to slip and create extreme heat. If the clutch face is discoulored that is possibly the case. You may also see some epoxy from the coil windings that may be there as well. To see if this is the problem, start the tractor and trun all of the accessories on. With a volt meter check the voltage to the clutch and make sure it's to the manufacturer's specs. If the voltage is all right then there is a proble with high head pressure.

Compressor Diagnosis by Oil colour

Did you know that the refrigerant oil colour can oftem provide us with some idea of the conpressor and internal system conditions?

Black Oil indicates carbonization caused by air (moisture) in the system. Brown Oil indicates copper plating caused by moisture in the system. Grey or Metallic Oil indicates bearing wear or piston scoring. Piston scoring may be attributed to high head pressure caused by system moisture.