AC Issues

jv982 · Aug 22, 2007

So last summer I replaced the compressor, accumulator, orfice tube, and all of the o-rings for a R134 conversion. The AC was blowing COLD, like 37f cold.

Now I am having issues with the AC again. My compressor will run when the truck is idling, but if I rev it over 1500rpm for more than 5 seconds it shuts off. It will turn itself back on when I return the engine to idle. It does this when driving, or sitting still. Even when the compressor is running it does not produce any cold air.

Also, my low pressure line does not get cold or show any condensed water on it. Last summer it would have a tiny bit of frost right after the accumulator on it, but now it is hot.

Any ideas?

baddis · Aug 22, 2007

the way it sounds you have a leak and the system charge is low. the easy way to check is to look for oily spots at connections and in your condenser. if this doesn't work then you will have to get the dye and a black light.

jv982 · Aug 22, 2007

If I had a leak, why would my compressor shut off when the engine spun faster?

MAKG · Aug 22, 2007

Because it's low-side pressure regulated.

You don't think the compressor spins all the time, do you? That part of the behavior is COMPLETELY normal. It's the warm air that isn't.

You need a shop. If you don't understand how the system works, you have little chance of correct diagnosis and virtually no chance of a correct repair.

baddis · Aug 22, 2007

you beat me to an answer but mine was pretty much the same

jv982 · Aug 22, 2007

I must have miscommunicated my issue here...

The compressor turns off and stays off when the engine is spinning faster than idle.
It will turn on for about 2 seconds, and then stay off for several minutes. That is not normal.

I understand how a/c systems work, but I do not understand why the compressor would not run while the engine is spinning faster. Please explain.

Does Ford have performance tests that say that at a certain temp with the engine at a certain speed the pressures should be _?

*edit* And I will be doing all of this work at a shop, with access to a/c equipment. I am not just replacing parts and throwing cans of refrigerant at it. I am looking for a technical explanation.

baddis · Aug 22, 2007

you don't have enough refigerant in the system. the low pressure switch will not allow the compressor to stay engaged. i don't know all the specifics but listen to makg he knows his stuff.

jv982 · Aug 22, 2007

I would be happy to listen to him, as I always have listened to his advise, but he has not explained anything for me.

baddis · Aug 22, 2007

[QUO7068]TE=MAKG;Because it's low-side pressure regulated.[/QUOTE]

meaning the system is low of charge

MAKG said:
You don't think the compressor spins all the time, do you? That part of the behavior is COMPLETELY normal. It's the warm air that isn't.

the compressor will only run part of the time until the temp is reached then the compressor shuts down

[QUO7068]TE=MAKG;You need a shop. If you don't understand how the system works, you have little chance of correct diagnosis and virtually no chance of a correct repair.[/QUOTE]

if you don't know anything about a/c systems they are dangerous to work with with threat of damaging you 1 year old parts,hurting yourself or others.

RobbieD · Aug 22, 2007

One thought that comes to mind, as the compessor spools up with more RPM, is that the compressor's demand of the low refrigerant pulls the pressure down on the low side, tripping the low pressure switch. Just a guess.

jv982 · Aug 22, 2007

Honestly baddis I don't think you understand any of this. You don't even understand what MAKG has stated.

baddis said:
[QUO7068]TE=MAKG;Because it's low-side pressure regulated.

meaning the system is low of charge

low-side pressure regulated means that whether the compressor runs or not is determined by the pressure on the low side

baddis said:
the compressor will only run part of the time until the temp is reached then the compressor shuts down

This is not climate control with a thermostat like a house. The compressor does not shut off because it has cooled to a certain temperature.

baddis said:
[QUO7068]TE=MAKG;You need a shop. If you don't understand how the system works, you have little chance of correct diagnosis and virtually no chance of a correct repair.

if you don't know anything about a/c systems they are dangerous to work with with threat of damaging you 1 year old parts,hurting yourself or others.

Now you are just being a smarta$$. Surely you don't think I need that explained to me.

MAKG · Aug 22, 2007

And if it's NEVER turning back on, it's a good bet your orifice tube is plugged. You confirm this with a high side measurement -- it will get extremely high in that 5 sec or so. Note this can CAUSE leaks on the high side (it can get THAT high -- and from experience the pressure relief valve isn't always the first thing to pop).

Which is usually the result of incorrect charging, flushing, or assembly (introduction of contaminants, including "stop leak" and water vapor).

Ford has a lot of P-T diagrams, as well has cycle times, and so on. But they aren't the same for R-134a and it's hard to satisfy the conditions (interior "stabilized" to 70 deg F).

jv982 · Aug 22, 2007

RobbieD said:
One thought that comes to mind, as the compessor spools up with more RPM, is that the compressor's demand of the low refrigerant pulls the pressure down on the low side, tripping the low pressure switch. Just a guess.

That is a good thought, but I wouldn't think that would keep the compressor off almost entirely at higher RPM's. I could be wrong

MAKG said:
And if it's NEVER turning back on, it's a good bet your orifice tube is plugged. You confirm this with a high side measurement -- it will get extremely high in that 5 sec or so. Note this can CAUSE leaks on the high side (it can get THAT high -- and from experience the pressure relief valve isn't always the first thing to pop).

Which is usually the result of incorrect charging, flushing, or assembly (introduction of contaminants, including "stop leak" and water vapor).

Ford has a lot of P-T diagrams, as well has cycle times, and so on. But they aren't the same for R-134a and it's hard to satisfy the conditions (interior "stabilized" to 70 deg F).

Now the orfice tube being plugged makes perfect sence. If it is blocked it would let enough pressure through when the compressor is spinning at idle but when it spins faster it would starve the low side. Is that what you are saying MAKG?

Now no "stop leak" or other has been added ever. How would water vapor clog the orfice tube?

MAKG, Please confirm for me a super high pressure on the high side

MAKG · Aug 22, 2007

Water vapor can plug the orifice tube in two ways:

1. Corrosion products circulate and collect on the high side of the tube.

2. The vapor deposits on the LOW side as ice.

I'd suspect #1 under the cirumstances.

I've also seen orifice tubes plug from failing compressors, pressure lines, and even accumulator/driers. If a plug confirms, you'll find the residue all over the orifice tube. If it's the compressor, it will be magnetic and might even have chunks in it.

I'm making wild guesses here, but perhaps you're "compacting" the deposits above idle more than at idle. It's not COMPLETELY plugged, since a few minutes gives you a cycle back. But it sounds pretty plugged up.

jv982 · Aug 22, 2007

MAKG, Please confirm for me a super high pressure on the high side.

I will confirm the guage readings before I open the system up (after capturing the refrigerant), but it sounds like I need to flush the sys. and replace the accumulator and orfice tube. Hopefully thats it.

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