When in doubt, blame the sealant.
Ivor Matanle explains rumours and counter rumours that are doing the trade no good.
Vehicle air conditioning has now been around for long enough in Europe for there to be plenty of middle-aged air-conditioned vehicles of comparatively low value on the road.
Work on elderly air conditioning systems, especially where defective components have to be replaced, can sometimes cost more than the vehicle is worth.
But the hard fact is that working on an old system can take as much time as working on a new one, sometimes more. As a result, it is increasingly common for the potential cost of curing leaks by replacing components in old a/c systems to be uneconomic from the car owner’s standpoint. The risk then is that the car will be driven away unrepaired, leaking refrigerant and damaging the environment.
A solution to at least some instances of this problem, now widely available in Europe as it has been in the USA for decades, is to use air conditioning system sealants. However, there is a snag. Unless sealants are used by trained professionals who understand what they are doing and have the right equipment, they can cause problems. As in any field, problems caused by faulty installation and slovenly use tend to get blamed on the product, so there are those who will tell you not to touch a/c sealants with the proverbial barge pole. Those people are plain wrong.
What is needed is a clear understanding of the nature of sealants, of how and when they should be used, and of how potential problems can reliably be avoided. Used correctly, sealants reduce environmental damage caused by unrepaired air conditioning systems and can, in the right circumstances, enable drivers of middle-aged cars to benefit from effective air-conditioning for years longer without major cost.
The nature of a/c sealants
Sealants are fluids that are added to the refrigerant circuit of automotive air-conditioning systems. They come in two broad types:
Sealants that soften and rejuvenate the elastomers that are used for seals and O-rings in the system and that become hardened with age. The sealant restores their flexibility and sealing ability, preventing leakage through the seals.
Sealants which, when they encounter water, solidify to block small leaks in metal pipes or components. The principle is that, where there is a leak, the rush of refrigerant through the hole cools the refrigerant, liberating water from it as condensate. The water thus deposited around the leak solidifies the sealant that it encounters in the refrigerant, blocking off the leak. Once the leak is sealed, the condensation stops, and no more of the sealant becomes solidified.
Some manufacturers offer products designed to do both jobs – Primalec’s Airco-Seal Pro is one of these.
The sealants that cause the most controversy are the second type, designed to seal small leaks in metal pipes and components. The active component is a cryosilene compound, such as organosilane, introduced as a liquid to circulate with the refrigerant and designed to solidify in the presence of water. Provided that the compound encounters only moisture caused by condensation at the site of a leak, there is no problem. However, the sealant is unable to distinguish between condensate and water already in the system as a contaminant. Therefore the key requirement is that the air-conditioning unit is dry before it is refilled and the sealant is added.
When sealants should be used
First, it should be recognised that all sealants are intended for use in vehicles already several years old. They are not an appropriate approach to leaks in almost new vehicles, or cars just out of warranty whose value merits the cost of replacing faulty parts.
It is essential that an accurate diagnosis of the size and number of leaks in an air-conditioning system is made before the decision to use sealants is taken. Cryosilene sealants, such as Airco-Seal Pro from the UK manufacturer, Primalec, are effective only for small leaks. Several small leaks are fine. One large leak is not suitable for sealant treatment. As a guide, Primalec states that Airco-Seal Pro is suitable for systems that take at least two weeks to lose a substantial part of the refrigerant. If the system is unable to hold at least a partial charge for at least 24 hours, then the leak is outside the range suitable for sealants.
How sealants should be used
First check that the extent of the leakage is not more than the sealant can handle. Pull a vacuum in the system for five minutes. If you cannot reach 25” of vacuum within five minutes and then hold it above 23” for a further five minutes, then the leak is probably too large for effective sealing.
Check that there is no leakage through the compressor shaft seal – sealants are not effective with shaft seal leakage.
Always change the filter/dryer. Many problems are caused by inexperienced or slovenly operators who think they can get away with not changing the dryer. The desiccant in a used dryer cartridge, by its nature, contains water. If that water comes into contact with a Cryosilene sealant, the sealant will solidify, destroying the filter/dryer and potentially damaging the system extensively.
Evacuate the unit and hold a 29” vacuum for at least half an hour.
Attach the tap hose of the sealant container to the low pressure port of the air-conditioning system. Evacuate for a further minute to remove air from the tap hose, then take the tap hose off the low pressure port.
Charge the unit with the specified amount of refrigerant, then start the engine with the a/c unit switched on. Check the system thoroughly to ensure that it is working properly.
Insert the appropriate amount of sealant and run the a/c system for at least twenty minutes. The sealant will now circulate with the refrigerant, sealing any small leaks as it finds them. At the next maintenance session, the sealant will leave with the refrigerant and some of the system lubricant.
What about effects on workshop equipment?
If the workshop system is kept clean and dry, and serviced correctly, there is no reason why the use of sealants should block or damage equipment. Of course, sloppy maintenance of equipment can cause problems, with sealants as with other materials and procedures. One of the problems that cause workshops to have doubts about sealants is that the warranties on air-conditioning workshop equipment may state that the introduction of materials other than refrigerants and lubricants into the equipment invalidates the warranty. This is an understandable element of caution by the manufacturers. However, no problem will occur if the installation of sealants is carried out exactly according to the sealant manufacturer’s instructions. The same applies to warranties on air-conditioning components. As an added safeguard, a Primalec product called Recycle Guard can be used to filter all oil, dye and sealant from the refrigerant before it enters the workshop equipment.
The DIY effect.
A lot of the ugly rumours that sometimes surface about sealants have arisen from the extensive availability of a/c sealants in DIY supermarkets in the USA. DIY users of the materials rarely have the proper equipment for the job and, in USA, have on many occasions used sealants when they were not appropriate, or without changing the filter/dryer, or even without first discharging and recharging the system. When the system fails as a result of their efforts, they predictably take the car to an air-conditioning specialist, usually without telling him that they have added sealant. If the specialist does not use diagnostic equipment capable of identifying if a sealant is present, and, if it is, which sealant is in the system, the specialist’s workshop equipment is likely to be hard hit. The manufacturer of the workshop equipment objects to the claim and blames the sealant, whereupon the aircon specialist decides never again to allow sealants to darken his door. Once again, the fault lies not with the sealant but with the way in which it was installed.
Fortunately, DIY availability of sealants in the UK and elsewhere in Europe is minimal and DIY work on air conditioning systems is rare.
The other big source of potential trouble is when a less-than-scrupulous workshop owner spots the opportunity to generate turnover from the owners of older cars by offering sealant treatment as a universal low-cost means of fast air-conditioning repair. Or, of course, when a back street car trader sees it as a fit-and-forget way of selling on cars with a spot of aircon trouble. In either case, even if they have the right equipment and do the job properly, a proportion of the vehicles they treat will have bigger leaks than are appropriate for sealants. Or they will neglect to change the filter/dryer. You get the picture.
Richard Doran of Primalec, one of Europe’s biggest manufacturers of air-conditioning servicing products is adamant that aircon workshops must regulate themselves.
"Bad workshop practice has the potential to destroy a large part of the air-conditioning servicing market and alienate customers." he explained "Insistence of proper training of anyone servicing air conditioning systems, particularly when they are using sealants, is essential. We are happy to advise workshops using Airco-Seal Pro, but is essential that questions are asked and advice given before the sealant is used."