Can the Roof Air Conditioner be Recharged? How do you troubleshoot?

JDxeper · June 16, 2009, 09:46 PM

How do you check the roof AC? It will run and will not cool! Can they be recharged? i??
JD

gromit440 · June 17, 2009, 09:55 AM

Hey JD,

Is it the fan that is running or both the fan and compressor? If just the fan is running, a start and/or run capacitor on the compressor may be all that's needed. If both are running, the system can be charged with freon. A leak test should be done first to see where the freon leak is and how bad it is. A very slow leak may allow for a charge that will last quite some time.

If it's a freon12 unit, a 12oz. can will cost about $50 to $100 if you can find one. I just had my daughter's car charged with freon12 at a local truck repair shop that has been in business for years and the owner had some squirreled away. The cost for the charge and labor was $100. A changeover from freon12 to freon 34a would probably be at least $150.

If it's a freon34a unit, a charge would be minimal.

Do you have a friend or know of someone that does HVAC work that could take a look at what you have and lend you their expertise and advice? To replace the unit would probably be in the $650 range, if you shop around. Or you could buy a unit and install it yourself to save a few bucks. Good luck!

Jeff

ibdilbert01 · June 17, 2009, 01:25 PM

Make sure the thermostat is working. If it doesn't click when you turn it down, it might be bad.

And as Jeff said, R12 units (Mainly the older air conditioners) can be expensive to fill.

Its really easy and cheap to convert a car over to 134A, but I don't know anybody who has done it with an RV Style AC Unit. R12 units used a form of mineral oil that keeps the compressor lubed. R134A will not mix with mineral oil and requires a different type of oil. If its an older unit, and it has a leak, it might be best to just replace it. (Of course thats nothing more than an opinion)

Heres a simple trouble shooting guide.
http://bryantrv.com/roofac2.html

I had ran across a better troubleshooting guide, but can't seem to find it. If I do, I'll post it here.

JDxeper · June 17, 2009, 04:09 PM

Thanks for the info, printed the trouble shooting guide, will look for the simple things first. If it gets complicated will try to find a friendly HVAC, person. If it gets too bad I can get a new Carrier V delivered for around $500 from one of friendly advertisers on the CW. I'll keep you posted. !:)!

Froggy1936 · June 17, 2009, 07:24 PM

The roof air is most likely charged with Freon 22 same as house A/C which is still available. Look on ID tag it will tell you which one it has in it. If there are no service valves, you can purchase the type that, when installed,and tightened, they punch a hole in a line and give you a service port for vacuuming and charging. They are supposed to be leak proof. If the system is empty, you will have to add some Freon and check for the leak with a electronic leak detector. Most leaks will have to be cleaned and silver soldered (if you can access them). If no leaks can be found, you can pump down a vacuum (with a vacuum pump), then close all valves. If it will hold a 29 in vacuum for 8 hrs, go ahead and recharge it (use at least i can with oil added).

Good Luck. Frank

nikoj · June 20, 2009, 11:42 PM

You first need to confirm that the compressor is actually running. Small a/c s typically use only one fan motor and it will run if the compressor is bad. Look for any oil in the unit, that will indicate high side leaks, but not necessarily low side ones. If the compressor is starting and air is moving inside and out it would be quite likely you have a refrigerant leak, but not definitively. If the compressor is not starting checking the value of the starting components is necessary. Small a/c units can be very primitive is this regard, I see small commercial systems that only have a run capacitor, typically oval shaped steel cans, but may be round, almost all run caps are steel cased. If you have a start cap it should be in a black plastic case. A typical range would be around 150-250 ufd. (microfared) A run cap has a much lower value, many units run about 12 ufd per ton. (12000 btuh) The start cap needs to be within +/- 20% of the rated value, +/- 10% for the run cap. They have to be checked with a capacitance meter, an ohm meter is not enough. The age of the ac is important - if its over 10 years old replace it, the rv ac's i've seen are like domestic refrigerators, factory sealed systems with no access - they generally work great for years but when they have a serious problem e.g. refrigerant leaks you just replace them. Age is important due to wear in the compressor and deterioration of the coils, other unpleasant problems can occur if you had a leak and sucked air into the system, moisture can be hard to get out of the oil and will cause acids to form. The good news is most ac problems are electrical in nature. Good luck.

Nick

jkilbert · August 31, 2009, 09:03 PM

as long as there is nothing wrong with the compressor thr rooftop units can be recharged. this is something that an hvac tech needs to do because you need a refrigeration license to purchase either r-12 or r-22 refrigerant. most of the units are r-22 like a residential unit. also if someone does this for you, insist on a sweat on schrader valve not a puncture valve. the puncture valves will eventually leak the you have to pay for everything all over again.

DaveVA78Chieftain · July 01, 2012, 04:43 PM

Now that we are a few more years down the road, I have a sneeky feeling the $ of R-22 has gone through the roof. Was watching a local news article recently that home AC recharge costs for any unit more than a couple of years old have gone through the roof. They no longer make the older refridgerent. Gotta love they way they make sure you are forced to buy a new unit on a semi-regular basis for home or RV.

Dave

Oz · July 01, 2012, 07:53 PM

That is correct, Dave. We had a few people with older cars ask the same question at my previous job. When I consulted the shop, they said it would be phenomenally... yes, I said, "phenomenally" expensive to recharge them since the supplies were dwindling and no more could be made.

hankf_52 · July 12, 2012, 05:51 PM

RedTek makes a product called 12a part nbr 313..to recharge r12 systems with an ozone safe product called 12a..it comes in a kit with (3) cans and a hose
check them out

piorun · July 12, 2012, 06:29 PM

I just recharged AC in my 85 Cadillac with R-12. It costed me $400. You can get probably anything it will just cost more

shaneperch · March 29, 2013, 09:38 AM

They are usually R22 units. if they are built before the 2000s There is a" drop in" refrigerant that will work with the oil in an r22 system. I think it is a 400 series refrigerant. I don't know what a new unit is today. I bought a new one in 1999 and I think it was 600 bucks i am sure they are more today. I think you should repair yours.

pvoth1111 · June 01, 2014, 11:23 PM

If the seal between the return and supply is not tight.....the cold air will blow under it and "satisfy" the tstat....I've had this issue on my front a/c.....if there is no oily residue on around the coils or piping it has all the Freon it ever had......check everything else first as the system wasn't meant to be opened up or added too.....once you open "with piercing valves" it may never seal 100% again......and then will have to be topped off often.....time to time....use an amp meter to confirm compressor works as needed....and keep clean the coils and filters.....