Hello all,

My 96 4.9 has apparently lost its will to make cold air for me. This is a tough call. Part of me figures it would be nutty to spend lots of money on a/c for a truck I drive a couple of days a week. My rainy day funds took a real beating of late. Part of me wants the a/c fixed yesterday

I have to check the simple stuff, such as whether the compressor is trying to run, but have some questions prior to that.

One thing I have noticed for a while is that a particular fitting has long looked like it might be leaking. Could it have leaked to the point that the pressure is too low for the compressor to run? Does that make sense? It does to me, but what about to someone who knows something about a/c repair?

My best guess is that if the repair is small, I will have the pros do it. If the system is a train wreck, then I would probably lean toward rebuilding myself and having it charged once it holds a vacuum.

The question is where to start. I have some material on a/c that I need to review. What if any gage+dye type of testing would you do before going to a shop to have it checked and and maybe recovered? I am willing to buy gages, but a vacuum pump and recovery system are a little much for me right now.

Bill

 

A vacuum pump costs about $15 at Harbor Freight. It's the kind that requires a compressor to operate. First you would need to see if all the freon has leaked out. Find the low side (not that it matters for this) and push in the valve stem. Yes you will leak a little into the atmosphere but if it's empty then you won't leak any. You should press it for a few seconds, if it's empty it will stop hissing after about a second. Throw the gauges and vacuum pump on and pump it out. After a half hour of pumping turn off the valves and see how fast the vacuum drops, if any. If the system won't pull vacuum or won't hold vacuum then there's a leak. If the hose looks like it is leaking then it may be, the rubber hoses are available at the parts store. I don't have any experience with the UV tracer dye, and the regular dye was difficult for me to see. I have an uncle with a sniffer that I borrow.

I could actually go on and on with questions and instructions. Is the system still R12 or has it been converted to R134A? Did the a/c stop suddenly or has it not worked in a while?

 

The R12 system was phased out in 93. As for the compressor being low, you can get a tester from any parts store with a can of R134a for around $20. if it's empty, and you want to know if the compressor's even half good still, grab the clutch, and turn it with your hand. if it doesn't budge, it's shot. if it turns relatively easily, then it's likely still good. As for the leak, I've found that the easy way is to get an ac adapter mounted on the end of a basic air compressor hose (this is assuming that there is NO refrigerant in the system), and pressurize the system, and check for leaks using soapy water. Then, fix the leak as needed, replace the accumulator, and orifice tube (and other parts needed). After that, vacuum test it and fill it up. If it doesn't function after that, I would look into the high,and low pressure switches, and the relay being functional. And yes, if there is too much, or too little pressure, it will shut the system down using those switches, so that it doesn't blow a line on the high side. If you know someone that works at a shop that offers that service, it can help also. The guage manifold, and lines are about $40 each at Advance. The vacuum can be bought for around $200 off a tool truck, and if it's leaked out, there's not much to recover until you get to the point of checking switches. The relay usually dies before the switches do though. Just make sure you replace the accumulator, and orifice tube if it's been empty for a while, becuase it will have built up moisture int he system, and that's a bad thing to have.

 

I'm not sure when R12 wasn't used anymore. Don't get the professional $200 vacuum pump, the $15 Harbor Freight one works just as good for a lot less money. It's not good for professional use because of the wear and tear on the air compressor needed to operate it.

 

I shall have to look into this Harbor Freight vacuum pump. Somehow the idea of spending nearly 1/8 of the price sounds good to me.

 

Here's mine. It's just a venturi vacuum pump. It still pulls about -30. My hand is there for size comparison.