I have a 1992 F-150 w/5.8. The truck was converted to R-134a some time ago (well before I bought it). The A/C worked very well when I bought the truck 4 years ago. However, towards the end of last summer, it stopped cooling, and the compressor began cycling rapidly when in A/C mode. Since it was getting cooler, I ignored it until now. I assumed it was low on refrigerant, and ordered a set of manifold gages last week so I could check the numbers and top it off. I have no prior A/C experience, and this is a "learn-as-I-go" deal.

After receiving the gages, and hooking them onto the system, I had a static (non-running) pressure of about 50-55 lbs. on both sides, and running (with the cycliing switch jumpered) was Low = 5, High = 100. From what I read on line this, along with a rapidly cycling compressor, indicated a low charge.

I found some old, dried oil residue around the cycling switch on the dryer, so I bought a new one and replaced it, along with the (green) O-ring. I hoped this was the leak that caused the whole problem as none of the other system components have any oil residue whatsoever. I keep the engine clean and detailed, so an oily connection would be obvious.

After replacing the cycling switch, I added one 12oz can of refrigerant, and the readings were: Low = 12, High = 145. The compressor was still cycling rapidly, so I had to jumper the cycling switch again to get these readings. An improvement, but not up to the numbers I read that it should be. Assuming it was still low on refrigerant, I added two more 12oz cans before I could get the compressor to settle down and stay running consistently on it's own.

When driving, my vent temperature was in the 65* range; too high from what I could gather. I added one more can, and was able to get the vent temperature to a low of 53*. The static readings after this were 72 lbs. and the running numbers were; Lo = 38, High 190. I had read that the low should be in the 20-30 range, and the high should be around 2x ambient temp (it was about 90 today. The low looked a little high, and the high seemed to be right in the ballkpark.

The problem is that I now only have a vent temp of around 65*-70*. I am not able to get back to the 53* I had earlier. The compressor still cycles rapidly at certain RPM's, and runs steadily at others. Lower RPM's seem to allow it to run steadily.

Also, I remember back when the system worked well, that the dryer always used to sweat, and feel cold to the touch, along with the large line running out the back and along the upper fire wall. Now, they're slightly cool, at best.

The small line (fluid?) that runs from the RH side of the compressor to the firewall box is warm to the touch until it reaches a coupling, and then it's VERY cold below the coupling. I'm assuming that's where the orifice tube is located. the high-side tube on the LH side of the condensor is very hot when running, just like it is supposed to be.

Also, I double-checked that my blend door was going all the way closed as it should by removing the glove box, and watching and feeling it as I turned the temperature ****.

Questions:

- Does the system sound like it's under-charged, or over-charged? I put in a total of 4-12oz cans. Seems like a lot.

- Is the cold line below the coupling on the RH side line correct?

- My compressor makes some noise (always has, even when the system was cold). Could this be an indicator of trouble? It seems like the wide pressure range from Low to High would indicate the compressor is relatively healthy.

- Does not having a cold dryer indicate that it might be blocked, etd?

Any other input, experience, or advise anyone can give will be much appreciated. Am I asking the right questions? Should I be looking elsewhere? Remember, I'm learning as I go, so all input is appreciated.

Thanks!

JD

 

Since your Compressor is still cycling and the vents temps are high, I would say you are low on refrigerant. I would add a little at a time, checking the low (suction) line(s) and dryer for maximum cool temps. You can overfill pretty quick with 134 so go slow until you get desirable vent temps. I would also suspicion that you are low on refrigerant oil but no way to be sure since you had the leak and do not know how much was lost.

 

General rule of thumb for R-134s conversion is to charge to 80% of the manufacturer's specification of R12. In your case your truck is rated at 44 ounces of R12. That would make your R-134a charge around 35 ounces. You have overcharged the system.

With your other symptoms of compressor noise, whacky low to high sides pressures and high vent temperatures sounds like you may have a bad compressor. These older Ford compressors are known to let loose internally which fills the system with black goo which in turns plugs up the orifice tube and lines the hoses with said black goo. The condition is referred to as Black Death.

Evacuating the system, opening it up to inspect the orifice tube will tell you the story of what is going on inside.

 

Yeah, a touch under 36 oz. is what I came up with using the 80% factor I found on line. That's why I'm also leaning toward over charged. I plan to dump out some refrigerant, and see if I can get it to work better.

I'd considered a compressor failure as well. But, it seemed to turn smoothly (I'll check again tonight), and I thought the low/high side pressures looked reasonable. If dumping refrigerant doesn't help, I'll open it up and look for signs of crud in the orifice tube. If I see anything like the photo in the link, I'll order a new compressor, condenser, orifice tube, and dryer/accumulator.

Do you think the evaporator and lines can be flushed adequately?

Thanks!

JD

 

You may have a clogged orifice tube. The line that runs from the condensor to the evaporator is called the "liquid line". Where it joins to the evaporator is where the orifice tube is. If it is super cold down under this connection, but just barely cool on the accumulator, then it sounds like not enough refrigerant is being returned to the compressor. It can't just be overcharged or else your high side would be over 300 - something else is going on.

 

On these older style condensers you stand a pretty good chance of getting it adequately flushed. The evaporator should be fairly easy as well.

 

Yes, the liquid line is warm from the condenser to the joint where I believe the orifice tube is. Below the joint, going into the evaporator, it is VERY cold. Does it sound like a partially clogged orifice tube?

Thanks!

JD

 

Thanks - I'd always had the "catastrophic failure" idea in the back of my mind, given how old the truck is. If I can save the evaporator and lines by flushing, it will reduce the project cost and time. I'm hoping I can flush/clean that big manifolded hose assembly that runs from the dryer to the compressor (low side) and from the compressor to the condenser (high side). That piece alone is about $100.

Thanks,

JD

 

I am just having the same problem on my system as you did,TX92. My A/C still runs r12 but is doing what you describe. I was going to get what is still in my system recovered. Then look at & repair & flush , pull vac. and use some r12. I still have five 12oz. cans and my system is 2lbs 12oz. if I remember correctly, but I'll have to check. Did you have an orifice tube blocked ? If so was your compressor bad? Just trying to cross my T's and dot my i's. I just don't want to waste what I have.

 

For starters, when you removed the cycling switch or Low Pressure switch you opened the system. once the system was opened you introduced air and moisture into the system, both of which are very bad for the system. So now you need to either buy a recovery system or take it to a shop to have the refrigerant recovered. Then you need to buy a vacuum pump, or while you are at the shop having the refrigerant recovered have them pull a deep vacuum on the system.

Chances are good that you now have ice partially blociking your orifice tube, and you are getting erratic readings from the combination of air and moisture and ice in the system.

Matt

 

what i read from the original posters post is that he opened the system to replace the "cycling switch" whatever that is. i am assuming he is talking about the low pressure switch. after he replaced it, he jumped it and put 4 cans of freon in.
this tells me it is not working properly because #1 he overcharged the system, and more importantly, #2, he never pulled a vacuum to evacuate the system before he charged it.
with these two mistakes, you will never get the AC to work properly.

 

Bingo. Air will cause high pressures and poor cooling. You need to have the system recovered and evacuated. You also should replace the accumulator and replace the oil in the system so that the R134a isn't mixing with the mineral oil and any remaining R12. The mineral oil and R134a are not compatible, you need to use ester oil or PAG oil. The desiccant in the accumulator also will be saturated and has probably absorbed moisture, hence why it should be replaced.