AC Issues

[jv982]

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]

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]

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

[MAKG]

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]

:agree: :damnit1: you beat me to an answer but mine was pretty much the same

[jv982]

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]

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]

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]

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

meaning the system is low of charge

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]

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]

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

[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


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.


[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]

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]

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


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]

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]

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.

[RobbieD]

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


Good point; the system would probably short cycle instead. MAKG's thoughts make sense, and I hope that you get it squared away with the least amount of hassle. Good luck!

[skippy]

it is hard to diagnose with out seeing the gages hooked up and being there to look at the behavior of your system but the info you have supplied us with suggest a system low on refrigerant,enough left to bring on the comressor but not enough to sustain the pressure above the low pressure cut-out setting of the lp switch or as whats-his-name said a high side restiction starving the low side and tripping the lp switch.in any case you mentioned access to a shop and proper equipment,put the gages on it,run it and see if low press drops out of sight,high side climbs out of sight just before it cycles off.if you have a halogen leak detector run a leak check at all connections and along the hoses,if you find a place that the leak detector acts up back up the detector with soap bubbles.pm me if you want,if your close to douglaville i can help you with it.good luck.

[jv982]

I am going to throw the guages on and see what I can see. I have access to an a/c machine, a refrigerant "sniffer". Unfortunately I do not have access to a machine that flushes out the a/c system.

Thanks for the offer... If I need assistance I will let you know.

[skippy]

i don,t have a machine to clean out either,we use dry nitrogen in residential/comercial systems for pressurizing systems for leak checks and flushing out systems.just a thought,pressure swiches go bad and i looked at mine,its out of the truck and it has a slotted screw between the wire terminals.if the system cuts out around 30 psi its probably best left alone.

[Boomer]

First of all go back to his first statement..."high pressure line doesn't get cold"...high pressure lines don't get cold when they are charged right...system is low

Next...at the end of last year a little frost formed on the high line...the only way that happens is when the freon boils off comming out of the condenser due to LOW SYSTEM PRESSURE. You have to maintain high pressure to keep that stuff from boiling off to soon (like outside the evap tubing). Think of it this way. Water boils at 212 degrees at sea level. Put a glass of water in a bell vacuum jar and drop the atmospheric pressure and the water will boil at room temp. Bottom line and most importantly as stated by MAKG...if system pressures are low you need a shop...in the very least you need what a shop has to do the job right.

[jv982]

First of all go back to his first statement..."high pressure line doesn't get cold"...high pressure lines don't get cold when they are charged right...system is low

Next...at the end of last year a little frost formed on the high line...the only way that happens is when the freon boils off comming out of the condenser due to LOW SYSTEM PRESSURE. You have to maintain high pressure to keep that stuff from boiling off to soon (like outside the evap tubing). Think of it this way. Water boils at 212 degrees at sea level. Put a glass of water in a bell vacuum jar and drop the atmospheric pressure and the water will boil at room temp. Bottom line and most importantly as stated by MAKG...if system pressures are low you need a shop...in the very least you need what a shop has to do the job right.

Please excuse my typo.... I am surprised you caught it as no one else did, or maybe they just knew what I was trying to say. I will edit it in the orginal post as well..... I meant the low pressure line after the accumulator.

[skippy]

i understood what he was saying.

[envious8420]

pressures above 300psi-500psi(edu guess)
sounds like it may also involve a pressure switch

[MAKG]

The pressure relief valve is supposed to pop at 450 PSI. Other high side leaks are unfortunately likely to show up well below that.

I doubt this involves the pressure switch, but it can be jumpered if needed.

[skippy]

when i get around to the a/c phase of my resto i will have a high side safety swich w/manual reset set below the relief valve setting.

[MAKG]

Bad pressure switches are MUCH more likely to be always on or always off, then just cutting out during operation. Or else they can get leaky. Note that these are tunable, so if they always cut out at 30 PSI, you can tune them to cut out at the proper 24 PSI. Or even a bit lower for R-134a (too low forms ice in the evaporator core and makes the airflow bad).

[skippy]

i know,im talking about adding a hp cutout as added protection.i have my accumulator and hoses off right now,i looked at the lp switch last night and was supprised to see the adjustment screw.don,t see that in my field unless its a bulky metal box with cap tube in various lenths ending with a 1/4" flare nut and a 1/2" conduit knock-out. our encapsilated switches come in various cut in/out settings some with 24"leads and some without but none i,ve seen with that adjustment screw,thats just plain cool.now that i know i,ll bench test mine w/dry nitrogen before i put it in.when i add the high pressure safety i will have the manual reset variety so i have to check it if it ever toggles.im in no hurry to get the air going,not my dd.need to make it more road worthy first.24 psi seems a little low but ok.