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Discussion Starter · #1 ·
Hi,
I have been having issues with my ac that I can't figure out. I am in process of moving from Cali to wash and towing a 20' cargo back and forth. Last trip ac compressor grenaded. When I got home I got and installed rock Auto kit with new compressor, condenser, dryer, and orifice. I did a flush of both lines and evaporator. Pulled a vac and left overnite, no leaks so charged to manual volume. Blew ice cold. Did fine around town for couple weeks.
Hooked up trailer and set off north. After about an hour, turned on AC and nothing but hot. Compressor was fast cycling about 5 sec on and 5 sec off. It was two days of hell at 95 plus degrees, thought wife would off me...
Get to wash, unload trailer and my ac toolkit was there. Hooked up gages and everything normal and was forming ice on both ends of cold line.
Hooked the trailer up to take some stuff to storage. On way home I turned on AC. High cycle of compressor and hot at vents again.
After I got home unhooked trailer and popped hood to see what was going on. Still high cycling of compressor so turned it off, connected my gages, and it ran normal. Ice cold at vents and normal cycling, ice on cold line. Gages read low 25, high 175, ambient about 75 deg.
What is happening here? Is there a temp sensor that I reach when pulling trailer? Is there an internal valve in compressor that could cause this?
I'm leaving to go back to Cali in couple of days and would like to have this resolved...
My truck is in good shape and only 150k miles. All systems working fine.
Thanks for any input!
Doug

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Definitely low on charge. Whether you have a leak or just didn’t charge it sufficiently the first time is unknowable. I would suggest using a dye containing refill can and get the pressure to 32-35 low side with engine at 1200 rpm doors open blower on high. Then, when you get settled, get the UV light out and find your leak.


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Discussion Starter · #3 ·
Thanks for your response. I charged it to the tag under the hood by weight. Should be correct unless new condenser is slightly larger volume.
Not sure charge is everything though as it still can go from fast cycling to normal operation in just a couple of minutes. I have not been able to get the gages on it when it is fast cycling but when it does this the cold line off the compressor is just as hot as the hot line in. When it operates normally the cold line and dryer form ice. It's like there is a blockage on the cold line and it cycles off the high pressure switch during high cycle times but that blockage disappears when cycling normally. I will have to get a gage on it when it's happening to know for certain, but I have no idea what sort of blockage could do this - like a valve going on/off. Very strange....

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A CCOT air conditioning system (like we have) should never form ice. That indicates the suction pressure is at a Pressure-Temperature point below freezing, which the low-pressure switch should prevent. Unlike HVAC systems, the compressor speed won't stay constant in an MVAC system. That makes setting charge by pressure challenging. Add to that the variable cooling across the condenser (wind speed) and you get into lots of fun. So, you sit there at idle and the system stays above the low-pressure limit and all is well. Then, you get on the road, towing nonetheless, and see your low side pressure plummet leading to the rapid cycling.

Ford did issue a TSB at some point raising the recommended charge by 4 ounces. Then - the new microchannel parallel flow condenser that out now decreases it significantly. Which condenser did you install? Was it the MOTORCRAFT YJ594? Did you put a red orifice tube in? You also mentioned leaving the vacuum overnight. Do you have a micron gauge or did you eyeball it on a dial gauge? I wonder if you truly had a full vacuum when you charged it.
 

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Discussion Starter · #6 ·
RT, lots here to unpack.
First, red orifice was installed
Condenser was not a Ford unit, I believe made by spectra. No way to tell if volume internal is same as Ford unit, no such documentation came with unit.
I only have the standard analog high/low gage set. When I pulled vacuum, I ran pump until gage settled at lowest reading plus 45 minutes more runtime. Gage indicated 29 in I believe. Gage was in same position in morning when I checked for any leak, ran pump for another 15 min before disconnecting it and starting to fill from cans.
I filled to the weight on the underwood tag using a postal scale to determine partial can at end.
Sounds like the consensus is that I am undercharged and I should charge until low pressure is above 30psi at about 1100 from, max air, high fan, doors open, 75 ambient?
Thanks,
Doug

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Discussion Starter · #7 ·
RT,
I do have one of the hand held halogen sniffer gages and could not detect any leaks using that.
Thanks,
Doug

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Discussion Starter · #8 ·
Ok, hooked up gages and added some additional r134a. New results:
1100 rpm, high fan, max air, both doors open
32 low / 265 high
42° air from vent

600 rpm, same settings as above:
37 low / 215 high
45° air at vent

Compressor cycles less often at low fan settings now. Will have to drive it a bit to see if this was the fix. I added about 3-4 ounces estimate.

Please let me know if these numbers seem in line with expected?
Thanks,
Doug

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I think you are on the right track. One thing people fail to realize, especially on these small (relative) systems is the refrigerant loss in the high-pressure hose can easily be a couple of ounces. This, combined with the recognition by Ford that their charge value was already 4 ounces low can lead to issues. In the future, when you hook up gauges on an R134a system, unscrew the port depressor on the high side (effectively closing the high side port) and open your low and high side knobs on your gauge set with the yellow hose still attached to your closed refrigerant can. This will allow the suction side of the system to pull the liquid out of the high side hose. It's a bit hard to describe this exactly without knowing what gauge set you have. I have the Fieldpiece SMAN 480, which has 4 knobs. That behaves differently than an old analog 2 knob set as I can isolate my charge port and suction port. A little bit rambling, but the basic point is every time you put gauges on it, you are extracting enough liquid refrigerant to fill the red hose and manifold if you don't do the purge. And - I'm sure you know about purging the air out of the refrigerant lines when you attach them. Don't want to be injecting air into the system each time as well.
 

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Discussion Starter · #10 ·
I have the older 2 knob style gages. I do get what you are saying about loss when you connect though. Hopefully I will get a warm day soon so I can test further. Glad to hear I'm on the right track...
Thanks for all your input, explained things better for me ..

Doug

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...charged to manual volume.
What manual? What charge does it say?
I charged it to the tag under the hood by weight.
What weight does the tag show?
Hooked up gages and everything normal...
What gauge readings do you consider normal?
...and was forming ice on both ends of cold line.
That's not normal, and it proves that the low-side pressure is dropping low enough for the temperature to be well below 32°F.
Gages read low 25, high 175, ambient about 75 deg.
That's on the verge of too low for the clutch to stay engaged, if the low-pressure switch is adjusted properly. This shows the correct pressure settings for each refrigerant, so ignore the first one for R12:

(click this text)


This shows how to adjust the low switch, but it's written for R12, so ignore the pressure given here:

(click this text)
Is there a temp sensor...?
No.
Is there an internal valve in compressor that could cause this?
No.

This page shows & explains how to install an R134a system in these trucks:

(click this text)
 

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Discussion Starter · #12 ·
Got home, and threw the gages on when temps were higher. It was turning off on the high pressure sensor.
Bled off some charge until it was going off on the low sensor but high pressure was still climbing faster than normal.
Had system evacuated and pulled the orifice. It was black and covered in chips, another grenaded pump.
Weird as everything that was not replaced with new was flushed with solvent flush several times. I drained out all the oil shipped in the pump to get the volume and added to the tag amount plus about one oz as some always gets away.
No reason I can think of why the pump went out.
New coming from rock Auto and Warranty returning the old stuff.
Please let me know if I missed anything obvious?
Thanks,
Doug

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isn't there a filter inline? trash in line from my understanding will crash the comp.
also, check vacuum it may be insufficient to switch the gates on blower system.
I re built mine about 10 yrs. ago and still ice cold. Seems I remember a filter.
 

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It was turning off on the high pressure sensor. ...another grenaded pump. No reason I can think of why the pump went out. ... Please let me know if I missed anything obvious?
The obvious answer is that it had too much refrigerant (overcharged) which naturally led to liquid entering the compressor, which hydraulic'ed it, just like water going into the engine would do. This is why refrigerant work should be left to pros. If you make even a small mistake, you can grenade the compressor, which then puts shrapnel through the manifold hose & into the condenser, which cannot be reliably cleaned, so it has to be replaced at the same time as the compressor, orifice, refrigerant, & oil.

Take it to a pro.
 
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