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Discussion Starter #1
I am finally getting round to fixing the air conditioning system on this 1990 bronco 5.0. The bronco had been parked for at least 10 years and there was very little pressure in the system. I converted the system over to R134 by replacing the compressor, condenser, dryer, clutch cycling switch, o-rings and red orifice tube. Funny thing is this already had some green o-rings in it so maybe it's been worked on before. I took it to a shop and had them pull a vacuum, confirm no leaks and charge the system. Here is the head scratcher. With the engine running and the AC on max the high side pressure is around 100psi (it's about 60 degrees in the garage), the low pressure builds to about 45psi and the compressor kicks on. When the compressor kicks on the high side pressure goes to about 150 and the low side pressure drops down to about 22-24psi. The compressor stays engaged for about 2 seconds then disengages. It then takes about 8-10 seconds for the low pressure to build back up to 45psi and the cycle repeats.
  • No cold air comes out of the vents even when I jumper across the cycling switch. It's actually warm air (warmer than ambient temps)
  • I have tried a different cycling switch
  • adjusted one cycling switch by turning it counterclockwise 1/8 of a turn.
  • removed the cycling switch and placed a jumper wire across the plug. The compressor stays and the pressure remains low. I forgot to document the pressure reading I'll try it again this evening.
My current theory is that I put the orifice tube in upside down. Is that even possible?

The tech who did the recharge did not know what the problem was and I didn't want to pay them to trouble shoot it yet.

Any other suggestions?
 

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Our 1981 Bronco was doing that same thing.... it was simply a low charge of R134. I just went out to the Bronco because I remembered that I had the tech use a sharpie to write the charge amount on the label under the hood...... 2.3 lbs. He had gotten close with the conversion chart, but ended up at 2.3 lbs by observing the gauges.

I replaced the entire AC system on our Bronco, except for the high and low side hoses. Turns out that was a mistake because the high-side hose had pinhole leaks along the length of the hose, causing the refrigerant to leak slowly over the course of a few days. They verified that it was leaking by applying air pressure to the system through their gauges and squirting the hoses and connections with soapy water.

My local Bumper to Bumper store made me a new hose. Once I got that installed and had the system recharged, it worked like a champ.... 45 degrees from the vents!

I don't recall if the orifice tube can be installed backwards or not.
 

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You could install a orfiice upside down but would be very hard. Unlikely

Suck the system down again. And make sure your vacumm holds. When I have time. I like to vacuum test old systems for 2hrs or more. You can also do the Hi air psi in system and soap and water test also

Most common prob if its not a leak. Is charge level or oil levels wrong

MAKE sure you have dye in the system also

Good luck & Happy Holidays.
 

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Discussion Starter #4
Thanks for the suggestions. Before taking it to the shop for a recharge, I pulled a vacuum and let it sit for 1 hour with no change in pressure. After that I pulled vacuum for another half hour. The tech pulled vacuum for 30 minutes before charging it.

When I get home I'm going to check the static pressure as I rough indicator of refrigerant level. Next I'll jumper across the cycling switch and observe the gauges to see if it gives any clues. I'm pretty much out of ideas after that.
 

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Purists would not recommend this.I hooked up a toggle switch on the dash, "hot" to the Compressor.

Works for me, summer I'll run for a while and shut it off for minute or two, hasn't blown up yet.

Good luck, sometimes AC problems can be the worst. I had something called "Black Death", caused by incompatibility of oils when using Synthetic R12. Had to clean and recharge the system.
 

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The idea of a toggle switch for the A/C clutch is good. I have one on our 1969 Ford Falcon Futura wagon that a previous owner installed. I like it!
8C75FD5A-D363-414B-B020-76CE9F75CE4F.jpeg
 

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Discussion Starter #7 (Edited)
Well, the static pressure indicates that there is enough 134 in the system. About 58psi at 60 degrees.

I bypassed the cycling switch, when the compressor kicks on, the low side pressure dropped to almost zero so I pulled the jumper wire to shut it off.

What would cause the low side pressure to go so low while the high side pressure was normal?

I'm thinking about recovering the 134, open it up and inspect everything again. Maybe I've missed something.
 

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1996 EB 5.8L, E4OD, 2.5" RC Lift, 33" tires, 3.55 gears
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I’m no AC expert but I recently replaced my entire A/C system in my 96. I agree that it is a good idea to capture the 134 and recheck for leaks. It’s possible that your leak doesn’t show up when vacuum is pulled and only leaks under pressure. That happened to me. Mine would hold vacuum for hours but the moment I pressurized the system and sprayed soapy water, I found a leak. I didn’t recharge until the system held pressure and passed the soapy water test and then held vacuum overnight.

I’d also be weary of giving too much credence to static pressures. just my .02. Good luck
 

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My current theory is that I put the orifice tube in upside down. Is that even possible?
Yes. I did it in a ranger once. It was a pain to pull out too. It defintely sounds like something's clogged down there. That there is an overpressure on the high side and underpressure on the low side indicates refridgerant isn't moving like it should be and the orifice tube closing off on pressure because it's in backwards wouldn't surprise me.
 

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If you do go this route, be careful pulling it out, IIRC mine broke in half when I pulled it out and that lead to a lot of awkward prodding to remove the bits that remained in the tube.
 
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