It's happened again, and I'm getting really tired of it. Yet another call from a boat owner who called in what he thought was a trained and experienced marine refrigeration technician to fix a poorly performing system, and now it's working worse than it was before! Why? Because the technician had added refrigerant, or "put in a shot of Freon" to what previously was a perfectly charged system.
Our office here spends way too much time on the phone and in e-mails helping customers correct mistakes made by mostly well intentioned but misinformed and inexperienced technicians. Too often it seems that adding refrigerant has been a Hail Mary move, made after diagnosis was unsuccessful, and done in an effort to show the customer that at least something had been done. And that's where all the problems start ....
A capillary tube (cap tube) refrigeration system contains a very precise amount of refrigerant. There is no reservoir or holding tank for excess refrigerant, and over-charging will inevitably result in poor performance. The system will be either perfectly charged, or over-charged, or under-charged, and once the equilibrium has been upset on a perfectly charged system, it may take quite some time and effort to return it to its perfectly charged state. This is true also of the majority of air conditioners installed on small/medium size boats, as these are also cap tube systems.
So you have a problem with your cap tube system and you have someone purporting to be a marine refrigeration specialist come take a look at it. But before letting anyone loose in your bilges and cockpit locker, you'd best consider referring to the Rules of Engagement below.
Rule No. 1 - Just because someone comes brandishing a set of refrigeration gauges and what seems like a highfalutin qualification in marine refrigeration and air conditioning from a marine standards organization doesn't guarantee that they actually know what they are doing.
Rule No.2 - Never let any such technician referenced in Rule 1 above connect refrigerant gauges to your system without him/her giving you a detailed description of what he/she thinks the problem may be and why they feel the need to attach said gauges. Hint: If the problem is that the compressor is not coming on, there is no need to attach gauges.
Rule No. 3 - Never, ever, let a technician add refrigerant to your system without explaining exactly why he/she thinks this to be absolutely necessary.
Rule No. 4 - Ask the technician what method he intends to use to gauge the level of refrigerant in your cap tube system. If they say weight and/or pressures, tell them to instead check the frost-line, as described here: Frigoboat R134a Charge Guidelines
Rule No. 5 – If the technician thinks your system needs refrigerant, then that implies there is a leak. No point in putting more gas in a system that has a hole in it. Tell your tech to find and fix the hole first, then add refrigerant. Think of a car tire – if it's punctured, why keep pumping it up without fixing the problem first.
Rule No. 6 – Have the technician agree that if it later transpires that he/she had added refrigerant to the system unnecessarily resulting in an overcharged system, said technician will return and correct the refrigerant charge at no additional cost to you, no matter how many repeat visits this entails.
Rule No. 7 – Never, ever, ever-ever, let anyone (including yourselves dear boat owners) inject refrigerant laced with additives like leak detecting fluid, "conditioner", extra oil, etc., into your cap tube system. I know those products look mighty attractive on the shelf at Pep Boys, but the only thing allowed into your system is pure unadulterated refrigerant R134a.
Rule No. 8 – The telephone rule. The use of a cell phone by a technician to call the refrigeration system manufacturer for guidance can be either a good thing or a not so good thing. If the call is made early in the service visit because the technician is not sure what is going on, and before he/she has messed with anything, then this can be considered to be a good thing. Disappointing yes, but at least the tech is honest! If the call is made in desperation after all else has failed and the system has by then been flooded with excess refrigerant, then this is a very bad thing.
So there you have some Rules of Engagement that may help you avoid turning a simple problem into a nightmare. Cap tube systems are inheritantly very simple, but technicians need to think twice before "shooting it up with Freon."