Servicing Volvo Climate Control Systems

Volvos built for the U.S. are equipped with a climate control system that comes standard in most models. The climate control system contains a function selector dial, driver and passenger temperature dials, a recirculated air switch, A/C on and off switch and a fan speed (blower motor) control switch (See photo 1).

The heater-A/C blower motor is controlled by the Electronic Climate Control (ECC) output power stage, as the air conditioning system operates only above 32° F. If the blower control switch is in the off position, the A/C compressor will not engage. Some additional components used for this type of system include a sun sensor, outside temperature sensor, low-pressure switch, interior temperature sensor, four damper door motors, high-pressure sensor, engine coolant temperature sensor and the A/C main relay.

Climate control services can range from needing to recharge the system, to performing major component repairs, such as a condenser or an evaporator replacement. This article will cover the climate control system on 850, V70 and S70 models, which are most common.

COMPRESSOR CLUTCH CONTROLS

The A/C clutch is activated by the engine management system. The ECC unit requests activation using an A/C selected signal to the engine control unit via the low-pressure switch. The engine control unit (ECU) determines when the A/C compressor kicks in based on the engine temperature signal, pressure signal from the pressure sensor and accelerator position.

A few months ago, we had a customer's Volvo in our shop that had a mysterious problem with the A/C-heater system. At times, there was no air coming from the dash vents at idle or while the car was being driven. It was an intermittent problem; the fan was still working but no air was circulating at all.

The way I found the problem was when I discovered that the A/C compressor was not cycling; it was on all the time! The customer bought the Volvo used and there was a problem with the ECU. It was obvious that the technician who formerly serviced the vehicle didn't understand the system. He jumped the main A/C relay, energizing the A/C compressor clutch, which caused the evaporator to freeze and restrict air flow to the main heater-A/C box where the air is distributed. The fix was to replace the ECU and recheck all of the other systems.

A/C PRESSURE SWITCHES

The A/C compressor is connected in series with the high-pressure switch, low-pressure switch and the safety switch. The high-pressure and the safety switches cut off power to the A/C compressor if the pressures become excessive. They then supply a signal to the ECU to run the cooling fan. The low-pressure switch turns the A/C compressor on and off to maintain pressures within the limits.

TEMPERATURE SENSORS

The outside temperature sensor is mounted just below the glove box door and sends notice of any temperature changes from the cabin to the control unit. The passenger compartment temperature sensor, with an integrated fan, is located in the center of the dash panel. The resistance of the air temperature sensor decreases as the temperature increases. The solar/sun sensor is located on the top center of the dash panel; it's a photodiode that generates current when exposed to sunlight.

AIR DISTRIBUTION CONTROLS

The air distribution control is based on signals coming from the ECC unit, which adjusts the ventilation and defroster/floor damper door motor. The ventilation air distribution setting is selected if the driver's side control panel is set for maximum cooling. The floor/defrost setting is selected if maximum heating is selected. The defrost/air setting is selected if the engine is cold and outside and interior temperatures are also low.

RECIRCULATED AIR SETTING

The ECC unit selects the recirculated air mode to provide cooling only when high outside temperatures exist, provided that:

1. There are considerable differences between the desired and ambient temperature on the driver's side.
2. A high fan speed is manually selected. In this case, the recirculation damper will be set to a mid-position. Only 50 percent of the air will be recirculated.
3. The off position of the recirculation switch corresponds to the automatic operation; the ECC unit determines whether recirculation is required.

DAMPER MOTORS

The temperature control damper motor, recirculation damper motor and floor/defroster/ventilation damper motor are all identical, but their control range varies according to the damper being controlled. Damper motors have a position sensor to enable the ECC unit to determine the damper position, learn damper limit positions and to detect any fault in the motor. The floor/defroster/ventilation damper is operated by one motor and linkage.

SELF DIAGNOSTICS

The ECC unit can detect faults in the system and store diagnostic trouble codes (DTCs). If a fault is present, the system informs the driver by flashing the orange A/C and recirculation button areas for 20 seconds.

The fault warning is given when a fault is discovered or present each time the ignition is turned on or the engine is started. DTCs will remain stored until cleared.

There are five different test modes/settings that can be selected for the reading of DTCs and other diagnostic functions. The best way is to use the Volvo Scan Tool 998 8686 or equivalent for pulling fault codes. Connect to the datalink connector located in the console (See photo 2).

The most common area for A/C refrigerant leaks in the 850 and 70 models is the evaporator. To test it, add some dye and give it a small charge. Run the system and use the black light to detect small leaks at the water drain located below the main housing. If there is no evidence of a leak at this point, remove the right lower dash and glove box assembly. Then remove the speed control unit that is attached to the main housing. Look in that area with the black light for wet and oily spots. Dirt and grime cling to a leaking evaporator. That is a telltale sign of leakage and restricted air flow to all areas.

EVAPORATOR CORE REPLACEMENT

Whenever the A/C evaporator needs to be replaced, the main dash must be removed. The main dash consists of five primary sections - upper frame, lower frame (left and right), dashboard cover and the lower console section. All the main sections are glued together and can't be separated.

1. Disconnect the negative battery cable.
2. Disable the air bag system. Pull out the main plug on the air bag control module in the center console. Then remove both bags from the car.

3. From the engine compartment, remove the windshield wiper nuts and windshield wiper well cover panel screws. Remove the wiper motor mountings (See photo 3).
4. From the passenger compartment, remove the steering wheel and position it relative to the steering wheel shaft. Before removing the steering wheel stalks, mark the sliding shaft with typewriter correction fluid, so it can be installed the same way with the steering wheel centered.
5. Remove the steering wheel stalk connector and remove the left and right soundproofing, side defroster, left- and right-side speaker covers and speakers. Remove the dash cluster and main wire harness. Be careful not to scratch or mark the clear plastic cluster.
6. Remove the dashboard mounting screws and glove box. Remove the radio and A/C control panel knobs with all the retaining screws. Disconnect the connectors and remove the A/C heater control panel from the dashboard. Remove the center console and both seat heater switches. Pull out the radio and disconnect all the wires with the antenna cable.

7. From under the hood, clamp off the heater core hoses and unbolt the evaporator housing from the firewall, slide out the unit and place it on a workbench (See photo 4).
8. Check the heater core for leaks in the lower center section of the main case. Replace it if any coolant residue is noted.
9. Reinstall components in the reverse order and vacuum/recharge the system. Check for leaks, add coolant and make certain that the air bag contact reel is in the correct location, as it will be damaged and will need replacement if it's out of time (See photo 5).
10. Road-test the car and check that the steering wheel is centered when driving in a straight line.
11. To prevent having unhappy customers, install the correct code for radio. If no code is available, you'll need to contact Volvo.

Climate control repairs could bring in high profits for import specialist shops in all types of weather. Performing the various diagnostic tests will save your technicians time and prevent customer complaints.

Volvo Climate Control Service Tips: Low blower circulation could be caused by a leaking evaporator that is spewing out refrigerant and compressor oil, which could then eventually clog the evaporator. Check the cabin air filter, shown below, which could also be clogged. Check all engine and transmission mounts for movement as they will put a strain on the A/C lines and hoses, causing leaks. The upper torque arm/mount bushing should also be periodically checked Check cooling fan operation. A non-functional cooling fan could elevate the high-side pressures, causing low evaporator temperatures. Noisy A/C compressors could be caused from too much refrigerant. When the pressure is too high, it could freeze the evaporator. Check the serpentine belt for cracks as the load from the compressor could cause it to fail. Also check the timing belt, since it also takes more load when the compressor is engaged. Raise the car on a lift and check the condenser for leaks (wet oil spots) that are a telltale sign of refrigerant oil. - by Boe Kalinoski.

COOLANT Q&A How do extended-life antifreeze and coolants differ from conventional antifreeze and coolants? The main difference is in the protection they provide against damaging rust and corrosion in the cooling system. With conventional antifreeze, key inhibitors, such as silicate, phosphate and borate, can start to deplete after just 24,000 miles. This can diminish the protection of the cooling system. However, extended-life coolants (ELC), which are based on organic acid technology (OAT) and are free of the conventional inhibitors, utilize advanced inhibitors to provide maximum protection for the cooling system for up to five years/150,000 miles, when a complete flush and fill is performed. Because the chemistry is different in conventional coolant and ELC, it is not advisable to mix the two products. Although the antifreezes are compatible, the inhibitors do not work together. Topping off ELC with conventional coolant dilutes the corrosion inhibitors in the ELC, reducing the usable life of the coolant to that of a conventional antifreeze. Likewise, topping off conventional coolant with ELC does not impart extended-life characteristics to the conventional coolant. In an emergency situation, when extended life antifreeze is not available it is advisable to top off with water to hold you over until you get more ELC. - Courtesy of PEAK Performance Products, Old World Industries. Tech Hotline 1-800-477-5847.

A/C Performance Checks: Check that air blows from all the panel vents in the dash area with the mode control on vent position, and that the recirculation mode is working. Check the condenser cooling fan when the compressor is engaged. Then start the engine and warm it up to normal operating temperature. Turn on the blower fan switch to high speed and ensure that the recirculated air switch is on. Make sure that the windows, engine hood and doors are closed, then run the engine at around 1,500-1,600 rpm. Place the A/C thermometer in the center dash vent and check the temperature after a few minutes to stabilize the air flow. Check the temperature using the chart below. - by Boe Kalinoski.

Protecting Your Customers' Engine Cooling System When the A/C is operated, there is additional load placed upon the engine and engine cooling system. To prevent overheating the engine during operation of the A/C system, the engine cooling system fan(s) must be properly operating and the coolant level must be correct. If the coolant level is low, it should be replenished. However, the days of just adding some green coolant are over. Today, the coolant is chemically different for many vehicles. Keeping a cooling system in chemical balance requires the proper coolant. The wrong coolant could result in costly coolant system and engine repairs. Today, there are many different colored coolants to help identify what's in the system. And not only is the proper coolant required, but also the proper mixture of coolant and water. To achieve long-life engine coolant chemical stability, follow the vehicle manufacturers' recommended service procedures. - Courtesy of the Mobile Air Conditioning Society (MACS).