Vanagon air conditioning becomes a hot topic every Spring. The camper crowd readies their Vanagons for summer travel. We often have customers who want to revive their air conditioners. Some of those vehicles are just low on Freon, many have been too low for too long. Here is the gist of how to evaluate and repair that system. First a few facts should be acknowledged. Unlike almost all the cars in our fleet, Vanagon air conditioning is not linked in any way to the vehicle’s cabin heating and ventilation system. In many cars, the air conditioner compressor is on automatically, and one has to choose the ECON setting to turn it off. Some cars automatically engage the A/C with the defroster as the dry air clears fogging quickly. In all cases, the air conditioner blows through the vents used by the climate control. The Vanagon however has the air conditioner completely separate from the heater in both the camper and regular versions. For many folks, their Vanagon is not their primary car, some are only driven a dozen times per year, or less. This sets the stage for the long term lack of usage of the A/C system.
Let’s take a moment to explain the Air Conditioning Cycle for those who might need a little coaching. Automotive air conditioning works on the same principal as refrigerators for houses, liquid evaporation. A suitable Freon gas gets compressed, then cooled to liquid form, which basically takes heat out of the Freon and into the ambient outside air. When that liquid Freon gets sprayed through a small hole and evaporates into a gas, it rapidly cools. Inside cabin air gets blown over the cold evaporator, cooling the passenger compartment.
Freon is a gas at room temperature, and a liquid when at pressures above around 80 psi at room temperature. A typical A/C system consists of a compressor, a condenser, a receiver/drier, an expansion valve, and an evaporator. A belt driven off the crankshaft spins an electrically activated clutch on the compressor. When the clutch is engaged, the compressor uses engine power to compress Freon gas up to a couple hundred psi. The Freon is now a high pressure / high temperature gas. The condenser in front of the radiator uses air movement from driving and/or the radiator fan to condense the Freon into a liquid, more precisely, a high pressure / high temperature liquid. The Freon temperature drops somewhat while going through the condenser, but it is still way hotter than ambient temperatures. The Freon then goes to a receiver/drier which has a filter and a desiccant bag to remove any debris and water. The high pressure / high temperature liquid now sprays through the expansion valve into the evaporator. The expansion valve has a tiny adjustable orifice which changes size according to evaporator temperature. The liquid sprays and evaporates into a low pressure / low temperature gas. Once the evaporator cools down to wherever the thermostat on the dash is set, the clutch shuts off the compressor until the evaporator warms back up. A quick touch on the hoses at the compressor will clue one about the system working. The high side should be about boiling hot, and low side should be freezing cold.
This article is all about Vanagon air conditioning. Modern cars have a fixed orifice and a variable compressor. The clutch turns on once, and then compressor runs continuously. The system varies the pressures electronically on demand to keep the evaporator constantly cold. Vanagon air conditioning is old school and far simpler. The gist of this article applies to other older models.
Almost every car air conditioning system seeps some Freon. Just a handful will make it 10 years without needing a recharge. Most systems need the Freon recharged every 5 to 8 years. Older systems like a Vanagon may need recharging more often. The main reason is that the compressor shaft has a seal between the Freon and the outside world, and it is the nature of a seal to seep very slowly to allow lubrication of the seal. The oil seals in an engine seep very slowly, hopefully so slowly as to not leave even a visible trace. Vanagon A/C systems have about around 8 ounces of lubricating oil circulating through the system, and a little oil comes out when the Freon seeps. As a gas, Freon is much more capable of seeping past a seal, as evidenced by the damp clutch face on many compressors. Any long term Freon seep or leak will leave some damp trace.
Freon has a normal pressure approximately equal to the degrees of ambient temperature in Fahrenheit. When the level of Freon drops near empty, the pressure drops until the damp ambient air can get back in wherever the Freon came out, especially when cooling off at night after the engine gets everything hot. Corrosion begins where the system is the coldest, in the evaporator. Evaporators are built like radiators, many hundreds of tiny internal passageways. Even slight corrosion starts to choke off and insulate the walls of the evaporator, and the system will not cool as well as designed. Normal A/C outlet temperatures are between 38 °F and 42 °F. Last century, Karmakanix would replace a corroded evaporator if the outlet temperature could not get down to 55 °F. Replacing an evaporator is an all day job, with 2 people needed for part of it. As the job is so expensive, we have now shifted our arbitrary limit to around 70 °F. Even 70 degree air feels good when the world around you is well over 100 °F.
Vanagon Air Conditioning Revival
Now how to revive Vanagon air conditioning systems. First and foremost, all Vanagon A/C systems were originally charged with R-12, the bane of the ozone layer. Most have been converted to R-134a, but if not, the conversion must be performed. Karmakanix maintains an old A/C machine just for draining and storing R-12, although most old and unused Vanagon A/C systems come in empty.
Next, an inspection: Check all fittings for the dampness indicating seepage. Check if the radiator fan comes on at its first speed when the A/C is turned on. Make sure the A/C evaporator fans work on all speeds. Try spinning the compressor clutch and compressor by hand. And finally, dry run the compressor momentarily to check for loud noises, which will require a jumper for power to the compressor clutch if the system is empty. The electrical system for the A/C needs to be checked for melting fuse connections and burned wires. On about half of the cars, the strap fuse is warped or creased, and some of the wires and connectors have been overheated.
Next the A/C system is drained and evacuated to at least 30″ Hg of vacuum and left for 20-30 minutes as an initial leak check. R-134a conversion is performed if needed by removing the old schrader valves and installing the R-134a service valves. If the system was empty, then a preliminary test charge of Freon is loaded and the system run. Check for rust in the Freon through the sight glass on the receiver/drier. The compressor noise level is reviewed after some minutes of operation. The low side and high side pressures are evaluated.
We make sure that the high speed radiator fan runs when the A/C high side pressure gets close to 250 psi. We find that many if not most of the pressure switches that generate the signal to run the high speed radiator fan do not work. The switch should close around 220-240 psi. when the switch fails, the high side pressure gets too high, potentially over 350 psi and up to 400 psi. This can cause high side hose, condenser or receiver/drier failure.
The outlet temperature at the evaporator is checked. If very little or no cooling occurs, then the system is not recoverable without changing all components and the job ends there. Only a handful are that bad off. If the system has passed all the initial tests, and the outlet temperature is low enough, then we perform a final leak test with an electronic leak detector. If that test is good, then we are done.
If rust is present, the system must be run, evacuated and recharged; and the process repeated until the Freon runs clean. The system should then be left under a high vacuum for at least a half an hour. The vacuum will cause any remaining moisture to vaporize, and that water can be removed when draining the system again. Then the receiver/drier must be replaced, as the desiccant bag inside is all used up.
Any connections that show any signs of seepage must have their O rings replaced. Vanagon air conditioning may seep at the condenser O rings, due to the high temperatures; and/or at the compressor due to temperature and vibration. The Vanagon air conditioning system converted to R-134a requires less Freon than the original R-12 charge capacity. The specification for R-134a is 1250 grams. After the final charge, the outlet temperature gets checked, then a leak check is performed with an electronic tester that is highly sensitive. If previous leakage has been an issue, we may put in some UV dye for future leak checking. It will show up bright yellow when illuminated with a UV light source.
To sum up, any Vanagon air conditioning system can be resuscitated. There really is no average cost, since every one has had a different history. If the system is clean, the cost is minimal. Many will need some o rings, the strap fuse and connectors, and maybe a high pressure fan switch replaced. The occasional rusty system will likely cost over a grand to revive. It may be worth it to some to replace an evaporator or even an entire system. Have a conversation with your Service Advisor about your expectations before the job begins. A working air conditioner can really make the different between a pleasant vacation and a Trip from Hell.