I have a '91 Explorer with a malfunctioning (R12) A/C.
Earlier this season the A/C was working, but not real cold. When the temps hit on the 90's, I added my last can of freon. After adding the freon, I found that the compressor clutch was not cycling. The air is very cold, but I am concerned that the system might be overfilled.
Questions: How do I test to see if the system is overcharged? How can I check to see if the cycling problem is due to a bad cycle switch? I am assuming that running the compressor at a 100% duty cycle will damage the system. Is this correct?
I have a hard time getting mine (when fully charged) to cycle off on a hot day. Did you try it early in the morning or late at night?
To test my system on my newer Explorer with the other refrigerant (whatever it's called) I use a pressure gauge that came with an A/C recharge kit. Older cars had a "sight glass" and you looked for bubbles when you turned off the A/C. You might have a hard time finding a kit for an R12 system at an auto parts store. eBay perhaps?
The A/C on some of the newer Explorers comes on with the defrost cycle and it's my understanding that on some cars once you turn on defrost the compressor will continue to be active until you turn off the engine so my guess would be that it's probably not real bad that it stays on.
My experience has been that if you are adding freon in hot weather it is darn near impossible to overfill a system. The only sure way to check overcharge is with gauges. I believe there is a high pressure blowout valve sticking out the back side of the compressor. If it's truly overfilled and runs way too much pressure that valve will blow out. The AC in these is marginal in hot weather so it would not surprise me that it needed to run constantly at this time of year.
Ashton, thanks for the reply. I have a set of gauges but the factory manual I have doesn't have any readings for them. So I wouldn't know how to interpret the readings. Any idea what they should read?
The A/C in this Explorer has always been real strong. And it was not uncommon that I could not run it full blast, even in the hottest weather. Now it's in the mid 90's, and the temp at the vents is well bellow 50.
Ballpark is that if you are running over about 250 on the high side it may be getting overcharged. That would be assuming you have normal low side pressure of around 25 to 35. The hotter it gets the higher the hi side pressure will be. And if there is a restriction in the system it might have hi pressure on both the low and high side or some other weird pressure split. On the newer systems (much newer then a first gen explorer) they use so little freon that it's just about impossible to charge based on pressures, you pretty much need to evacuate them and then put the exact charge back in. I think some are down to less then 8 ounces of freon. But even on these old explorers charging by pressure is hit or miss because so much of the "right" pressure is dependent on how hot (or cold) things are, engine speed, etc. They seem to have decided that assuming the system is otherwise ok it's just as well to simply feel the temperature of the inlet and outlet pipes of the evaporator. Plus they have an accumulator which holds excess freon so to some degree you can't overcharge anyway unless you manage to shove so much in that the accumulator can't hold it all. Pretty hard to do in hot weather.
Contrary to what you have been told, it is not only possible to overcharge a system no matter what the temp (excluding extreme cold) but it is possible to introduce enough refrigerant as to destroy the compressor if you are not familiar with the systems and their properties...
High side pressures are dependant upon ambient temperature and humidity.... rather than reinvent the wheel, I stumbled arouind in Google for a very few minutes and came up with this
formatting link
- I scanned throughit quickly and think it should answer all of your questions and do so withreasonably good answers... FWIW, low side pressures are "controlled' (notthe best word for what happens) by the low pressure cutout switch. The proper way to charge any AC system is by weight of the refrigerant... while you can sometimes get away with a SOTP gauge reference method, this may not be in anyones best interests... I haven't had to work with R12 systems for several years (they are nearly outlawed in Cananda... if you have one and it works - good for ya... if you have one and it don't - this gets gnarly... DIYers are allowed to do things that would have my licence revoked.
HTH
Top posted - as usual.
Somehow the old fool managed to hit "rely to sender" as opposed to "reply to group"...
Not sure who you are replying to. No one said it was impossible to overcharge a system. Try reading stuff BEFORE you respond to it.
As was already said had you bothered to read it first.
Not if you follow normal procedures for getting proper pressure readings and shunt the cutout.
That's true for *some* systems, which was mentioned. The manufacturers proper method as listed in repair manuals for many older systems includes both pressure readings, sight glass, and simply feeling the inlet and outlet tubes (or measuring them with a thermometer). Some systems, typically those with accumulators, have a diagnostic chart that can often lead to a point where the "next step" is to just put another pound of freon in and recheck. If that brings temps into range then it's "your done" in the diag chart.
Whatever works for ya. I'm keeping several old systems blowing cold on a variety of freon types. Last was a 91 Toyota. Instead of $400 or more in shop fees a $50 134a retro kit fixed it right up including the proper fittings. The 64 t-bird is pumping Freeze-12 thru it's icy hoses. I feed the 89 S-10 a can of r-12 every year or two.
Even on the oldest systems, there is a "best way" to do things.... This "best way" is to charge by weight. Are there guidelines regarding system performance - yes.... But your best results will be by charging by weight.... (Let's not belabour any environmental considerations). We can use the sight glass - the "electronic" sight glass, pressures - temperatures - or a combination of any of these.... None are truly accurate.
Guages are for performance testing systems and are not a real good measure of how much of what is in the system.... Look at it this way - there are those of us trying to treat "your" planet with the utmost respect..... the least you couild do is return the favour....
OK, for example, my '78 F350 says on the AC compressor how many pounds of R12 it should have in there. So, in order to do it by weight, does all of the R12 need to be evacuated and then replaced? This does not seem to be within the scope of most DIYers. Or is it?
Yes, the system needs to be evacuated. No... it isn't within the scope of most DIYers.... And this should be telling you something... I can't speak for the US - in Canada, if you have an R12 system that needs servicing, it will not be an R-12 system when you are done. As an automotive shop, we can't purchase R-12....
Open heart surgery isn't within the scope of most DIYers.... DNA testing isn't within the scope of DIYers.... closer to home - accurate (or properly performed) voltage drop testing... and we can add any number of other operations....
If we are not properly equipped to do something... why would we attempt? If I don't have the proper equipment in my shop to perform a test or repair on your car, will you pay me for the attempt?
Look at it this way... how can you ice skate if you don't have a pair of ice skates?
It is not necessary to do it by weight on those old systems. When they built em on the assembly line they obviously were not going to hook up a set of gauges to each vehicle to charge it. Once you know exactly how much it takes to fill up the system then when you are starting with an empty system it's duck soup to fill by weight and be done with it, they will all be the same. Once the vehicle is in service those hoses used back then will lose about a quarter pound of freon a year (modern barrier hoses lose almost nothing). Those systems were designed to have a reserve quantity of freon in them to provide a cushion against that expected loss. My experience has been that they held about 30% more then the minimum needed to cool properly. That's about a pound of freon. So once you start to notice reduced cooling those old systems can have another can of freon put in (not quite a pound) and they are good to go for another 3 to 5 years till the hoses seep out that reserve again. That assumes that the system is otherwise OK. Pressure gauges can help tell if the system is ok. Back to the original question, no, it is not necessary to evacuate and refill a 78 vintage system if all that's wrong is that it's low on freon. All that's needed is to add more freon.
As to DIYer, the main thing a DIY can't do is recover freon since the equipment is fairly expensive. But if the system has already leaked it all out you may not need to worry about it. It is possible to DIY quite a few of the repairs like replacing hoses, or compressor, or other parts. As with many things, you may need to buy some tools that are not a normal part of a DIY tool chest but the money you save can be spent on the tools. I bought a vacuum pump on ebay that works very well for just over $100. Gauges can be had for about $50. If you have an air compressor you can get a flush kit for around $50 in case you need to flush out some of the parts if the compressor did a "black death". If you don't want to use R-12 you can either convert to 134a or just use one of the so called "drop in" replacements like Freeze-12. There are plus's and minus's to each.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.