Tech Tips From RedDot – Heavy-duty A/C components rarely fail. In fact, the system fails the components because of contaminated refrigerant oil and general lack of preventive maintenance.
One of the best ways to improve uptime and reduce maintenance costs for the customer is to promote a basic visual check of major A/C components, hose connections, and fittings at regular intervals, like with every engine-oil change. This inspection routine has another benefit: it can generate business for your parts and service department.
Many A/C components are consumable items. It’s more cost-effective to replace them than to repair them. So preventive maintenance is an opportunity to sell a range of OEM-quality all-makes replacement parts for the air conditioner. Here are some examples:
1. RECEIVER DRIERS
The receiver-drier’s moisture indicator provides a quick visual cue about the refrigerant’s condition: a blue dot means the refrigerant is dry; pink, white, or grey indicates acid or moisture in the system. Checking the sight glass during an oil change or any scheduled maintenance procedure means the truck can receive necessary service while it’s there in the shop, before moisture and acid damage critical A/C components and lead to a failure on the road.
Dust, bugs, feathers, and other debris collect on the face of fins and tubes and act as a thermal barrier, making it hard for the condenser to shed heat. Condensers also fail because of vibration, which can cause hose connections to come loose and fatigue the condenser tubing adjacent to the fittings. Every 12 months, the condenser should be cleaned (taking special care not to bend or damage the fins) and the hose connections securely clamped.
3. COMPRESSOR/CLUTCH ASSEMBLY
The compressor provides the mechanical energy to circulate refrigerant and manipulate the pressure inside the system. It’s the heart of the A/C system, and the No. 1 HVAC maintenance expense item. Excessive noise and poor cooling performance are the two most obvious symptoms that a compressor is failing. Replacing the compressor involves pulling down the system, which adds refrigerant recovery and recharge to the repair cost.
Next time you see, “A/C won’t blow cold air” on a work order, note that the repair and downtime probably could have been avoided with a simple visual inspection of the truck’s air conditioning system. Any time you change the truck’s oil, check the A/C.
Arctic Traveler Canada is a master distributor and technical service expert for RedDOT. Call us today at 1-800-295-4156 for more HVAC solutions.
Before you pull the A/C compressor from a heavy-duty vehicle, take these steps to confirm that it really needs replacing:
1. Is The Compressor Rotation Smooth?
With the vehicle off, turn the compressor shaft with a 14-mm socket. If you feel grinding or hanging as you rotate the shaft, it’s probably due to broken components within the compressor. If the rotation is smooth, move on to Step 2.
2. Is The Coil Getting More Than 11.5 Volts?
Take a reading with the engine running and the clutch engaged. If there’s insufficient voltage, get to work on that. Otherwise, move on to Step 3.
3. Is The Coil Resistance Between 2.8 And 4.4 Ohms?
Any resistance outside this range will prevent the clutch from engaging or will cause used circuits to open. If the answer is yes, continue to Step 4.
4. Is The Compressor Able To Produce 350 Psig Or More?
If not, leave the compressor where it is. The system may have a low refrigerant charge because of a leak that needs repair, or a high-side blockage that limits refrigerant flow to the compressor.
Tech Tips from Red Dot
” We see lots of compressors that are returned fully functional and therefore not warrantable.
Get the diagnosis right. Perform a simple compressor function check before you pull the component from the vehicle.”
Tech Tips from Red Dot
1. Inspect Electrical Connections
As you perform a visual inspection under the hood (cab) and/or at the rooftop condenser, take a moment to check all electrical connections both visually and by feel. Make sure all leads and wires are properly supported and securely connected, and that there’s no corrosion or grime on the leads or connectors.
2. Check Electrical Current Flow and Device Functions
Perform the following steps to check current flow and electrical device functions:
- Turn on the ignition.
- Turn on the A/C system. This will power the thermostat and clutch. If it does not come on, use the A/C mode switch to check the leads to the switch. You should hear a “click” from the thermostat and hear the clutch drive plate “snap” against the clutch pulley.
- Check fuses. If all the connections are clean and tight and there’s still a failure, check the fuses in-cab as well as in-line.
- Check A/C clutch engagement. Since you can’t see and may not hear the clutch engage, get out and look at the clutch. If it’s engaged, you will see that the drive plate is against the pulley and not slightly spaced from it. If you aren’t sure the clutch is engaged, look for the lead wire connector near the clutch. Break and close that connection. The clutch will disengage and engage again.
- Test blower speed operation. Some systems have a common switch that turns on the air conditioner and powers the blower motor. Test blower speed operation by adjusting this or the separate blower control switch. Feeling the air flow from the ducts or note blower sound (speed) changes.
- Inspect roof-mounted condensers. Don’t forget to inspect roof-mounted condensers and A/C units for dirt and debris. Be sure the condenser fan(s) are working properly and all parts and electrical connections are securely fastened. The roof-mounted condenser fans may come on when the system is turned on. Like the thermostat and most clutches, the normal on-off cycling action can not be observed until the engine is running with the A/C system on.
Once your visual inspection is complete, talk to a qualified A/C technician about what you found. Your troubleshooting efforts will be rewarded with a speedier repair and perhaps a lower repair bill.
An electrical resistor whose resistance is greatly reduced by heating, used for measurement and control. Thermistors, derived from the term THERMaIly sensitive reslSTORS, are a very accurate and cost- effective sensor for measuring temperature.
Your HVAC Thermistor can be replaced with #1400K for Quicker Installation and Less Hassle!
Our Kit contains “First Fit OE Products” for longer life solutions to today’s A/C problems.
Check out the video courtsey of MEI here ….
A relatively new feature in the heavy duty industry, the cabin air filter is often overlooked in regular vehicle maintenance. That’s unfortunate because the cabin air filter is just as important to the passengers as the engine air filter is to the vehicle and a likely cause of “A/C Not Blowing Cold“. A cabin filter processes the air that enters the passenger compartment via the vehicle’s heating and air conditioning system, increasing passenger comfort by trapping particulates, pollen, and other irritants.
For people with allergies and other sensitivities to airborne agents, the cabin filter represents a significant advance. Replacing the cabin air filter at the recommended interval, or sooner especially in areas of high particulate, allows the A/C system to run at optimal efficiency and passengers to breathe cleaner, fresher air, which makes any journey more enjoyable – Courtesy of Denso Corporation
Remember to always use caution when performing preventative system maintenance, as ambient conditions (heat load) will increase refrigerant hose temperatures and don’t forget having the right quality parts on hand makes all the difference. See How To and Which Components to Inspect and watch this video to learn more about Basic A/C Troubleshooting.