DIY Auto A/C Recharge kit w/built-in gauge- worth a try?

[Vikas]

Can you explain why both high and low pressure gauges are absolutely necessary?

I personally have no problem if a competent and honest mechanic were to add the "missing" freon and the appropriate amount of oil and charge fair price for labor and parts. It is very frustrating and hard to find somebody who is both honest and competent.

The Arctic Freeze kit which I just purchased seems to have been used. The gauge is showing reading. If I press the trigger, somethings starts whoshing out from the adapter end. If I try to remove the nozzle by turning it counterclock wise, I start getting the whoosh again. It looks like nozzle has already puntured the can. So it is going back to the store. I need to consider do I exchange or just return it and try to get some quotes for A/C top-off service from local shops. One of the guy just quoted $35 per lb of freon + the whole nine yard of evacuation and refill!!! I don't think even R12 was that expensive when it because unavailable to general public.

- Vikas

 

[Test Specimen]

You need to know that the system is functioning correctly prior to using the pressures and temperatures to determine the refrigerant charge. If the compressor is not pumping well because of a failing valve plate, then having only the low side pressure gives you bad information. Even if the compressor is working well, the dial gauge assumes the evaporator temperature is at some value, and not every system has the same design temperature. The quality of the pressure gauge won't be very good either, considering they spent maybe 15 cents on the device. Trusting a 15 cent gauge to protect a $600 compressor seems risky.

Once you have assured yourself that both high side and low side pressures are normal, then you can calculate the subcooling of refrigerant liquid coming out of the condenser, or the superheat of the refrigerant vapor leaving the evaporator (for TXV controlled system only). Orifice tube controlled systems are run with a wet evaporator outlet, and won't have any superheat.

Most automotive technicians have no idea how to do this properly (no one ever taught them). They have been taught to remove the charge and weigh in the correct amount. The engineer who tests the system does a charge optimization process where they add a little bit if refrigerant at a time and measure the subcooling and superheat until they get the optimum performance from the system. I have had to do this on automotive A/C test stands where the original hoses have been replaced with custom ones, and it takes some time to do correctly.

Stationary HVAC/R technicians are taught the subcooling and superheat methods of charging. If you want to learn how to charge a system properly, read up on how they charge systems using pressure and temperature as compared to the saturation properties of the refrigerant.

 

[stogiedude]

I've pumped in a can of oil and a can or two of 134 once a year for around 3 years into my '94 Chrysler Concord AC. It's pretty simple to do and in my case it saved me from doing an expensive repair. The AC is nice and cold for the entire season for the cost of a can of oil and a can of 134 + the original cost of the recharge kit with the hoses and gauge.

Will it always work on every car? Of course not, but IMO it's worth a try if you just have a slow leak like my car.

I just tried to charge my newly acquired '94 Seville AC and it wouldn't work. I took it to my regular mechanic and he said the shraeder valve was bad. He replaced the shraeder valve, pumped up the system and I have nice cold air now.

Most places would have probably told me I need a new compressor or the expansion valve is bad or the evaporator needs to be replaced etc. It cost me $200 to have the valve replaced, charge up the AC system, replace the fuel filter and the air filter, which for some reason I didn't check when I got the car a couple of days ago.

To me it was worth the $200, but if the valve wasn't bad I would have charged the AC myself. If you can't get it to work, hopefully you have a decent mechanic who will fix what is actually wrong and for a reasonable price and not do ten other things that you don't need.

 

[johnsmith]

Just linking these two threads: http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=24;t=000449;p=1

 

[Chris142]

The old R12 systems were very forgiving. You could over or under charge a system and it would still work.

R134a is very unforgiving. A little off and you can blow hoses or damage a compressor.

The proper way to recharge a R134a system is to remove whats left, ck the orifice tube, vacuum and charge it to manufacturer spects.

If it's a custom system or you want to charge it w/o removing the refrigerant thats in the system, vacuming etc then you should have a high side guage, low side guage, know the ambiant temperature and have plenty of air across the condensor.

 

[Test Specimen]

I think this information needs to go in this thread as well as the preventive maintenance thread. There is a real benefit to having the correct amount of refrigerant in the system.

Undercharged systems will not carry the oil through the system as well as a properly charged system. If the oil hangs up in the evaporator because there isn't enough refrigerant velocity to push it out, you will probably have reduced compressor life.

If you overcharge the system, you will also probably have reduced compressor life because you will have excessive high side pressures, or get liquid refrigerant slugging back to the compressor that will wash out the lubricant from the bearings.

The dial pressure gauge on the recharge can won't tell you one way or the other. If you were able to measure the high and low side pressures, as well as the temperature of the lines leaving the two heat exchangers, you could determine if the system was properly charged. Otherwise, you have to weigh in the proper charge as determined by the engineer that designed the system based on the measurements they made while testng the system.

 

[Clement]

I used this same kit on my wifes car last summer, '94 Merc Sable. It took two cans of refrigerant to get the pressure on the dial up to where it was supposed to be. The AC worked fine all summer after that. I'll have to top it off again this year. I put one can in it to get it working (using the same gauge and 'spray' nozzel from last year) and it looks like it needs another.

I agree that from a purely mechanical point of view, it would be better to spent the multi hundreds of dollars and have a mechanic work on it, fix the leak, and refill the system. HOWEVER, from my point of view, It ain't worth it, especially if I can get it running for about $15 (2 cans of refrigerant).

 

[Drew99GT]

This is what happened when I tried using one of the ID low side gauges only. The thing kept reading slightly low, only for me to find out the system was dangerously overfilled. One thing with those low side DIY guages: it takes a while for the pressures to stabilize to where they're gonna be after you mess with the refrigerant charge. If you charge it and the gauge immediately shows it's smack dab in the middle of the blue, it may be in the yellow or red the next time you test it after you've used the A/C for a few hours. Another thing that will really boost A/C performance if the charge is good: clean the condernsor! I just did that the other day by taking the two fans off and running my shop vac in reverse and reverse blowing all the bugs and pebbles out. Once that was done, I took a tiny screwdriver and knife and straightened out the fins that were smacked shut by rocks and bugs as best I could. I ended up with a large accumulation of dead bug parts on my garage floor along with pebbles and rocks. Finally, after reading the post about bug screens in front of the rad/condenser, I rigged one up with 1.4 inch hardware cloth. That in and of itself made the A/C colder!

 

[mechtech]

file:///C:/Downloads/car%20info/index.cfm.htm
Automotive Air Conditioning Parts & Equipment - ACKITS.COM
This link has a temp/pressure relationship chart for R12 and R134, and would help.

 

[grm386wa]

I used to have a small buy here pay here car lot and we used these "home job recharge kits" all the time.

If you've paid $1000 for a car or got a car you don't want to start forking $$$ into, then what does it hurt to try a $30 fix?

I have nothing but raves for these AC recharge kits. The only time one didn't work is when the compressor was bad. And considering I only spent 1 can of "juice" to determine something other than a low freon was the cause of the AC not working correctly, I consider it a bargain.

If I had a car that was just out of warranty, Id probably have it diagnosed and fixed professionally.

 

[Vikas]

quote:

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Originally posted by stogiedude:

I just tried to charge my newly acquired '94 Seville AC and it wouldn't work. I took it to my regular mechanic and he said the shraeder valve was bad. He replaced the shraeder valve, pumped up the system and I have nice cold air now.

Most places would have probably told me I need a new compressor or the expansion valve is bad or the evaporator needs to be replaced etc. It cost me $200 to have the valve replaced, charge up the AC system, replace the fuel filter and the air filter, which for some reason I didn't check when I got the car a couple of days ago.

To me it was worth the $200, but if the valve wasn't bad I would have charged the AC myself. If you can't get it to work, hopefully you have a decent mechanic who will fix what is actually wrong and for a reasonable price and not do ten other things that you don't need.

---

I bet your mechanic is NOT the one who is associated with MACS otherwise he would have insisted on replacing lot more components claiming that since the A/C had not been working for quite a while, most of the component would be shot. At least that is what is spouted off by the conventional wisdom.

I feel that if the A/C had lost its maximum cooling capacity gradually over years due to attrition, then it makes perfect sense to add little more chemicals in it to make it up for the last charge. There is no reason why this can not be a starting poing for most of the cases when the car is over 5 years old and still has semi-functioning A/C.

But for a professional mechanic, this approach is NOT cost effective from *his* business perspective. He does not want $50 repair taking up a bay in his garage.

I have read enough professional auto repair press to know how the business is conducted. I usually ask for waiting appointment and scan through the trade press and sometimes I even ask them to borrow those magazines! Also most of those magazines have very good web sites with archived material e.g. Motor Magazine. Shops need to recoup the cost of the equipment which I do find extremely high even for simple machines. Entire industry is geared toward extracting as much money as possible from customer without completely turning him off. It is an art but once you add a nice waiting room with DVD player and kids' play area, people just don't think twice about paying somebody $300 to tell them that their brakes still are good at 15K miles. Yes, I am talking about proverbial 15K service on barely one year old car which has a list of "Inspect this" and "Inspect that". These guys don't even take the wheels off to measure the rotor thickness or runout or the pad material and still fleece the customers for $300+ Given that as a background, it makes perfect sense for a professional A/C shop to insist on $1000 repair once a cars gets in his shop.

Anybody wants to give the perspective from a garage owner?

- Vikas

 

[stogiedude]

I just got the car a few days ago and when I picked it up the AC was blowing cold. Within a couple of hours as I was transporting it home within less that 100 miles it stopped blowing cold. I doubt it was driven much recently. There are a lot of old people in Florida who keep their Cadillac in the garage and drive it infrequently. The car is in near mint condition. It's a '94 Seville and it only has 56K miles. I'm betting that the car sat for a long time and was only driven a few thousand miles per year for the last 12 years. I believe that the valve went bad recently rather than this being a long term problem with the AC.

I have gone to this mechanic many times with several different vehicles because he does what is necessary without doing a bunch of other things to inflate the cost. He's not the cheapest around, he charges $60 per hour for labor and he marks up parts a bit more than I would like, but over all he is a better deal that going somewhere else where they are going to take advantage of you and do a bunch of unnescessary things to inflate the cost.

When I was younger I did almost all of my own auto repairs, now I just take it in and have it done. I don't want to be bothered and I don't like getting my hands dirty. Cars are a lot more complicated to work on now too than when I started driving in 1975. I rely on my transportation too much to let myself-a weekend mechanic-try to figure out what's wrong and then try to fix it properly the first time. I really don't have the time to do it anyways.

If I can do some basic things like shoot some refrigerant in once a year and the AC blows cold for the entire season, that saves me a lot of money over a repair that could potentially cost hundereds of dollars. If I can change my oil and use exactly the oil and filter combination I want without driving somewhere and waiting and dealing with the people there, then that is something I will do.

If I can't figure out what's wrong right away then it goes to MY mechanic and he takes care of it and I know it will be done right. I've gone through a bunch of mechanics over the years trying to find one that I can even half trust.