I have a quick question about the AC in my truck. If I turn it on to max ac and the blower to high and let the truck idle the idle will go up and down consistently. I have no cold air coming out inside the truck. People have told me that this means the compressor is cycling through but is low on coolant. I have heard to stay away from the canned stuff you see at wal mart. How much should I expect to pay to get it done professionally. Also should the air just come out of the defroster vent?

 

I just had my a/c checked for leaks, o-rings changed going into the compressor or condensor or something along those lines, and recharged for 80 or so dollars at a local belle tire. to replace all the o-rings like i asked would have cost a fortune for it calls for 6+ hours of labor.

from what i learned from my recent post. the do-it yourself kits are temporary. find the leak and have it fixed.

 

it is not uncommon for R134 to leak out thru the hoses over several years. If you are loosing a 12 oz can per year or two, it would be worth just adding a can. If it leaks out in a month, then you need to find a leak and have it fixed. The $7 cans a Wal Mart are the same gas the repair shops put in. You need a $15 hose and low pressure gauge to install the can. You really need the gauge to determine what is inside. Open the hood and look at the compressor clutch. If it runs for a few seconds, then cuts out, its a good possibility that you need a little gas. I had a 78 Fairmont wagon years ago that used one can of R12 a year. Cost me $.79 a year to top off. Never had a reason to take it in for repairs.

 

The big issue with the cans available in the parts stores is that most of them contain additives, boosters, sealers and other junk that just doesn't belong in your AC system. Those are all snake oil prodcts designed to flush your wallet and can potentially harm your system. Unfortunately, these are the cans that conveniently come with a hose and (totally worthless) gauge already attached.

Topping off the system, although not recommended, should be done with VIRGIN R134a and a proper can tap and hose. The virgin refrigerant does not have a hose attached and is usually on the bottom shelf. You really need a manifold gauge set to read both pressures too, but that horse has been beaten to death.

The reason that topping off is not recommended these days is twofold:
-Modern compressors don't have an oil sump, the oil circulates through the system carried bt the refrigerant. Undercharging will starve the compressor for oil, overcharging can cause oil "slugging" or hydrolock.
-Modern systems hold much less refrigerant than older systems. The "window" between overcharged-properly charged-undercharged is much narrower, only a few ounces. A slight overcharge can also quickly raise the system pressure and damage the compressor.
Refrigerant should always be added into a hard vacuum by weight.

With that said,
To top off the system correctly:
-Set the engine to a high idle, about 1500 RPM. High Blower, MAX AC, doors open.
-Add refrigerant until the accumulator starts getting cool. Let the system stabilize for about 2 minutes.
-Add refrigerant 2-3 ounces at a time(A postal scale works well for weighing the cans), with 2 minute stabilizing time between shots, until the evaporator inlet and outlet pipes are the same temperature. Check the temperature after the 2 minute periods.
-Once the pipes are the same temperature...STOP. Adding refrigerant beyond that point can damage the compressor.

 

But before I take it in does it sound like the compressor is atleast trying to cycle on and off with the way the idle changes? I am ok with paying more money to have it done the right way if its going to last. But I know that replacing the compressor is expensive and if I have to replace I think Ill say forget it.

 

The compressor is probably just fine if it's not making noise (fine mechanically, see below).
You've likely got a leak somewhere and the low refrigerant level is causing the system to cycle. The leak is most likely at a hose connection and should be a simple fix. That's where 75-80% of AC system leaks show up.

There is a "chance" that the leak is from the compressor shaft seal or body seals, though. This would mean replacing the compressor. If that is cost prohibitive, try the top off procedure I mentioned. It should get you by until you can afford the repair, or maybe longer.
There is also a "chance" of an evaporator leak, but it's not very common on most Ford products.

You can often visually spot leaks in your AC system if you can follow the lines out from the compressor and back. Look for oily dirt accumulation on the hose connections, crimped fittings and compressor (clutch face and behind the pulley). Refrigerant carries oil out with it and the oil attracts dirt.

Oh, your airflow issue is usually caused by a vacuum leak in the vacuum supply line that goes from the vacuum reservoir into the firewall and to the heat/ac controls. I'm assuming the truck is a 97-03 F-series, your sig says 84 Bronco, but.... Look around the battery tray, the plastic vacuum line tends to break in that area.

Hope this helps, Tom