Keeping your coach HVAC humming

Summer is here, which is the hardest working season for your heating, ventilation and air conditioning (HVAC) system. Fortunately, it's easy to keep your A/C working through the hottest of days with a little preventative maintenance. Here's a handy guide to help you and your passengers stay cool on hot summer days. While the general principles in this article apply to all coach HVAC systems, for simplicity, the specific examples and photos are specific to newer J4500 coaches. Always refer to the maintenance manual for your coach for the details specific to your coach.

The A/C belt, compressor oil level and the system refrigerant level are all key components to avoid any A/C failures on the road and checking them should be part of your routine HVAC system inspections.

The tension and condition of the A/C compressor belt must first be checked with the engine NOT RUNNING. A Force / Deflection Tension Tester is used to check the belt for proper tension. On a new A/C compressor belt, the force used on the tester must be 20 lbs. to produce ½" of deflection at the midpoint. On a used A/C compressor belt, the force on the tester must be 17 lbs. (Refer to the decal on the engine compartment door for belt tensioning values.)  The condition of the belt is also important. If the belt is missing any ribs it must be replaced. While a small amount of cracking may be acceptable, it is best to reference the maintenance manual and/or the belt manufacturer's specifications and guidelines to determine when the belt should be replaced.

Then, with the engine and the HVAC system RUNNING, listen for abnormal noises from the compressor and the condenser and evaporator motors. Once the HVAC system has operated for at least 20 minutes, the compressor oil level may be checked. The oil level should be within the guidelines on the sight glass or the compressor housing (Fig.1). The refrigerant level must also be checked after 20 minutes of operation. The level can be verified through a sight glass located on the rear panel of baggage bay #3 on the left-hand road side (Fig.2). If the charge is low, bubbles can be seen in the sight glass. If the coach is equipped with a receiver tank, the lower sight glass should be full and the upper sight glass should be empty. ALWAYS USE EXTRA CAUTION WHEN WORKING WHILE THE ENGINE OR OTHER EQUIPMENT IS RUNNING.

Figure 1 Figure 2

The oil color may be used to help diagnose any problems with the system. If the oil is dark brown, black or if you see what appear to be some metallic inclusions, the A/C system will require a more thorough maintenance check. For your convenience, the table below shows the types of oil recommended for the different systems listed.

Carrier Thermo King
R134a R22 R134a R22
Castrol: Icematic SW68C Dupont: Zephron 150
Solest 35 150 SUS Viscosity (Std. mineral base)
Mobil: EAL Arctic 68 Sunoco: Sunisco 3GS
ICI: Emkarate RL68H Texaco: WF1 132 WF68
Compressor model 18-00059-XX: Alkybenzene

A weekly inspection consists of checking the condenser and evaporator coils and filters for cleanliness as they are key components for A/C efficiency. The driver's evaporator, located to the right of the driver behind the panel by the step well (as shown in Fig.3) has two filters to check. Once the panel is removed, the filters may be accessed. In addition, there are two filters on the main evaporator that can be accessed from the battery compartment (Fig.4). For coaches so equipped, the parcel rack evaporator filters are located on the parcel rack door (Fig.5).

Figure 3 Figure 4 Figure 5

The compressor crankshaft seal and the system refrigerant hoses must be checked for oil residue. The oil residue may indicate a leak; however, you should check the maintenance manual to determine what steps, if any, must be taken. The filter drier must be checked for any difference in temperature across the filter. It is located by the condenser, which can be accessed by opening the service door on the road side behind the third baggage bay (Fig.6). The operator may check the temperature by hand to feel any temperature difference.

The evaporator motor bearings and brushes should be checked at least once a month along with the A/C compressor mounting bolts and the HVAC harnesses. The evaporator motor is located in the third baggage bay behind the access panel. The bearings can be checked by listening to the motor for squealing or chattering noise. Access to the motor brushes is accomplished by removing the black covers on the motor (Fig.7).  If the brushes are more than ¾" shorter than their length when new, they must all be replaced. Because the brush length may be different on different motors, please refer to the MCI maintenance manual for your coach or the motor manufacturer's specifications for more specific details.

Figure 6 Figure 7

By doing these simple inspections your A/C should operate at its maximum efficiency, which in return will keep the driver and the passengers cool.

For more information, refer to Section 16 of the MCI Maintenance Manual for your coach or contact MCI technical support at 800-241-2947.

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