'99 F250 Super Duty- immediate low side drop

[69DropTop]

My compressor was leaking at the case where the two halves bolt together so I grabbed one out of the junkyard trying to save a little money. I installed the junkyard compressor, pulled a vacuum and it would drop about 5psi of vacuum every 5 mins or so. I decided to partially charge to see where the leak was and sure enough leaking in the same place as the last one. I decided to get a new compressor this time.

I flushed the condenser, evaporator, lines, installed a new orifice tube added the correct amount of oil and went to charge the system. I noticed that the compressor was cycling on and off a lot through the whole charging process. I looked at my gauges and it wouldn't take long at all for the low side to drop to about 20 and the compressor would shut off. I put the called for 40oz in but it kept doing this so I thought it might have wanted a little more refrigerant so I put about another 4 oz or so in but still had the same results.

The only thing I can think I might have done wrong is when I removed the lines from the condenser I didn't pay attention to which one went where. I searched the 'net and only found one diagram and it showed the high pressure line going to the top and liquid line going to the bottom so that's how I hooked them up.

I hooked the high side up and it never gets above 100psi since the compressor isn't on long and both sides are equal when the engine is off. I did have to bend one of the rubber hoses around pretty good to get it back in and routed properly, could that have caused this? I was thinking I forgot to put the orifice tube in but I remember putting it in and I believe it only goes in one way so I'm thinking that isn't the problem.

Anyone know what I should look at? Any advice would be much appreciated.

'99 F250 AC Lines Diagram.PNG (34.11 KiB) Viewed 9902 times

[69DropTop]

Someone told em the the orfice tube is clogged up, does that sound like a possibility? I flushed the condenser, lines, and evaporator very thoroughly with flushing agent and shop air. At this point I'm not sure what to do so was planning on pulling the orfice tube and if I don't see anything there install the new suction and discharge hose set I bought.

Is there anything else I should look at or do while I have the system open?

[bohica2xo]

You never stated the test conditions - Ambient air temperature / Cabin fan speed / vent temperature / engine speed / High aide pressure / low side pressure.

If you are above 80f ambient I would be inclined to recover it & check the orifice tube for debris. That is assuming that the evaporator has good airflow and that the high side pressure is not out of control.

I had a bad HPCO switch drive me nuts once. There are several things that could cause what you are seeing, we need to know more about what is happening.

[69DropTop]

I apologize for not providing info for the test conditions at the time but think I have it figured out.  Last night I disconnected the liquid line to evaporator connection and when I did the filter/screen half of the orifice tube came out with the liquid line.  I took a mirror and saw the other half of the orifice tube was way back in the evaporator tube.  I was afraid I wasn't going to be able to get it out but eventually between blowing compressed air from the other end of the evap and using a pick I was finally able to dig it out.  I'm going to pickup a new orifice tube, install, and recharge.



Has anyone ever heard of an orifice tube doing that or know what might have caused it?

[Dougflas]

quite common. The plastic falls apart and breaks.

[69DropTop]

quite common. The plastic falls apart and breaks.

I could see that but that was a brand new orifice tube, guess it happens but sucks and threw me for a good loop.

[69DropTop]

I installed a new orifice tube last night, vacuumed the system and then charged.  It was about 74 degrees outside.   When I went out for a test drive the best temp I would get out of the vent was about 45 degrees and it went up to 51 when I'm guessing the compressor was off.  With outside air temp only being 74 I would have expected to see at least 40 flat or maybe high 30s for air discharge temp.  After my test drive with the fan on medium-low I looked under the hood and saw the evap outlet tube had a noticeable layer of ice on it before the compressor shut off but I didn't notice ice on the evap inlet line so I rubbed my finger on it and there was the slightest amount of ice but not like the evap outlet.  When I had the fan on high and had it set to recirculate neither froze.  I don't have pressures right now but I do know when I got done charging, fan on high and Max A/C setting the low side was sitting right at 30 when the engine was at idle.



Do you think a little more refrigerant would help me see slightly lower discharge temps?

[Dougflas]

test conditions are rpm 1500 doors/windows open, fan on high speed set for max cooling. Fords had eractic cycling switches back then. Make sure you have the correct charge in the system.

[69DropTop]

I knew the fan was supposed to be on high and set on max but didn't know windows were supposed to be down or doors open. The sticker calls for 40oz. I put 3 12oz cans in and between 1/3 to a 1/2 of a 4th can. I did have a similar test scenario last night- fan on high, set on max a/c, held throttle about 1500-2000 rpm but windows were up and I was getting higher 40s out of the vent. The coldest temps I got were with the fan on low or medium low. I can try the same test tonight only more of what you described with the windows down.

[Tim]

Might have missed it. What are the low/high-pressure readings at 1500 rpm?