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AC Problem 400+psi High Side

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loudnslow

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The AC wasn't working when I got the blazer and I'm trying to get it straightened out.
Found a few leaks, replaced condenser, compressor (r4), accumulator, orifice tube.
Put in some oil, evacuated, added 2 cans of r134 into both ports with engine off.
At first the compressor was cycling quite a bit, but I didn't see pressure drop on low side. Then compressor started running for longer and longer and now the pressure on high side just keeps building. I've run it up to 450psi. Low side seems to stay around 90-100. Ambient low 80s. Fan is spinning, but hard to tell if it's fast enough (no overheating issues though)

To me this sounds like a blockage, but where? orifice tube?
I see in the shop manual that there is a pressure relief valve and high pressure switch, but little description. At what pressure do they activate? Just venting to atmosphere?
 
That sounds like it is way overcharged. Low pressure side should be around 30-35 PSI with R-134a. I know you said evacuated, but for how long? Typically you want to hit it with vacuum for around 15 minutes to remove any moisture in the system. You say 2 cans were added, but what size cans?

Typically when converting from R-12 to R134a you want about 80% of the charge weight that the R-12 calls for. So if it calls for 2 lbs, you want about 1.6 lbs or thereabouts. And remember that the oil counts on that, so it sounds to me like you are way overcharged. I haven't dealt with most of the late model versions, but I know the only one I have seen with a high pressure switch is after they went to full on R-134a from the factory. Normally I only see a low pressure switch at the accumulator, and I have never seen a pressure relief that would vent excess pressure. It is illegal to vent to the atmosphere, so I don't know how you could release the pressure legally without a capture system.

Edit: Also, never charge an AC system with the engine off and do not charge through the high pressure side. Charge should only be added through the low pressure port with the AC set to Max and fan on high, engine running, and jumper the low pressure switch if the clutch does not engage. You don't want to force the charge in, rather let it be drawn in by the compressor.
 
I added 2x 12oz cans. The capacity I found in the shop manual is 3lb8oz. I'll have to check on the exact definition but I believe that's not including the 11oz of oil.
I replaced the compressor so there was no refrigerant to begin with and I ran the pump for about 20 min then made sure it wasn't leaking (another 20min) and only then added the r134. I think it's unlikely that the system is overcharged...

I'll have to scan a page from the shop manual to show the pressure relief valve and high pressure switch. It's shown right on the compressor, but to be honest I didn't look for it on the physical part.

I didn't think it was an issue adding refrigerant to the high side with the engine off. The high side port is right in front of the orifice tube which is where the refrigerant will be liquid anyway. It could definitely be bad when engine is running since the pressure would be much higher than in the can. Am I missing something?
 
The high pressure switch should shut off the compressor at any pressure over 400 (usualy 380).

I agree with your thoughts that you may have a blockage someplace in the system. You did not mention what prompted the AC work in the first place. you did say you replaced the compressor, was there a catastrofic failure that may have thrown junk into the system?

I usually look for blockages by looking for the "cold spot". Any place you go from hot freon to cold freon there is a blockage or restriction. In a normally operating system there should only be one "block" in the system, the O-tube. if you have a transition point any place else in the system than the o-tube you have a block in that location.

If you cant find the block anyplace else I would guess you got some kind of debris in the O-tube clogging up the works. Recover the freon you have put in the system and inspect the o-tube.
 
The system cycles on when low side pressure is high enough, and off when low side pressure drops to a preset point. If it initially cycled normally or fast, then the low side was being drawn from and tripping the low pressure switch. Most likely it now has so much pressure that the low side never drops down and the high side continues to build contributing to the problem.

And I will stand by what I said about never charging a system without everything running. That is standard operating procedure for any AC system, and can cause damage when the system is not running during charging.

My guess is the orifice is now completely clogged from charging into the high side, and there is so much pressure now that the suction side cannot drop down.

That's my thoughts take them for what you will.
 
if you had a comp fail then you prob have a pluged orfice tube. and also trash in the system. you should have replaced the orfice tube / flushed the system / and new reciver dryer as it will hold trash also.

the 400 high side if prob from the pluged orfice tube and a build up of trash.

best get it checked out and try again.
 
rufusbooth said:
The high pressure switch should shut off the compressor at any pressure over 400 (usualy 380).
Click to expand...
I definitely saw it go close to 450. How is this done? bypass? It didn't look like a connection to the coil.
rufusbooth said:
You did not mention what prompted the AC work in the first place. you did say you replaced the compressor, was there a catastrofic failure that may have thrown junk into the system?
Click to expand...
The system was empty when I got the truck and wouldn't hold vacuum. Compressor and the condenser were leaking.
rufusbooth said:
I usually look for blockages by looking for the "cold spot". Any place you go from hot freon to cold freon there is a blockage or restriction. In a normally operating system there should only be one "block" in the system, the O-tube. if you have a transition point any place else in the system than the o-tube you have a block in that location.

If you cant find the block anyplace else I would guess you got some kind of debris in the O-tube clogging up the works. Recover the freon you have put in the system and inspect the o-tube.
Click to expand...
That's a good idea, I'll try it. It'd be strange for the o-tube to be clogged since I put a new one in yesterday, but it wouldn't be the 1st time a new part was broke.

lectric80 said:
My guess is the orifice is now completely clogged from charging into the high side, and there is so much pressure now that the suction side cannot drop down.
Click to expand...
Do you mean the liquid freon that was in the low side damaged the compressor and debris from it clogged the orifice?

sweetk30 said:
if you had a comp fail then you prob have a pluged orfice tube. and also trash in the system. you should have replaced the orfice tube / flushed the system / and new reciver dryer as it will hold trash also.

the 400 high side if prob from the pluged orfice tube and a build up of trash.

best get it checked out and try again.
Click to expand...
I used clean air to blow as much out of the evaporator and tubes as I could and replaced receiver/dryer, condenser, compressor, orifice tube.

Thanks for the ideas :)
 
More than likely the orifice is clogged.
Even though its new.
If a compressor fails, it puts debris all through the system. Air won't get it all out.

Plus, using shop air puts lots of moisture in the system. Never run shop air through a dryer.
You are probably going to have to use a liquid flush.
I don't know what they are using now. The good stuff got banned, but they got something you can use.

Don't use water of course<G>.

I have actually had to replace the condenser (ac radiator) because it had so much junk in it, it was cheaper to replace it.

If you do a flush, you will remove all the oil if you do it right.
Might be some in the compressor, but nowhere else.
So you will have to put a full oil charge in.

Putting liquid in on the high side, WITHOUT IT RUNNING, will not hurt anything. Its normal for it to see liquid.

However, if you are charging from a big can, its easy to overcharge that way, since you are putting it in a lot faster than with gas.

Bad news is, if you find metal in the orifice, you may have sucked some into the compressor. Plus you probably should replace the dryer...again.
They sell suction side filters. If you find a lot of trash, consider one. Cheaper than a compressor.

As for getting all the moisture out...
When I am doing HVAC work, I have a tank of dry nitrogen I use for flushing.
There is a procedure called breaking the vacuum.

No matter how hard a vacuum you pull, you can not get all the air and moisture out of a system.
Especially if its large.
So, you pull a hard vacuum.
Insert dry nitrogen at a point as far as possible from the vacuum point, and then suck it out.

Some manufactures required 3 breaks when replacing a compressor.


J.
 
Fordum said:
More than likely the orifice is clogged.
Even though its new.
If a compressor fails, it puts debris all through the system. Air won't get it all out.

Plus, using shop air puts lots of moisture in the system. Never run shop air through a dryer.
Click to expand...
Well, I have a separate filter/dryer that I use for special occasions like this when I need to not have any moisture.

There was some debris on the old orifice, but the screen wasn't completely blocked, so I'm not sure if there's really all that much trash in there. I also turned on the old compressor and it didn't sound too bad.
I'm going to look for a cold spot in the pipes first, but then break it apart, check out the orifice tube and try to find a blockage "manually".
 
loudnslow said:
There was some debris on the old orifice, but the screen wasn't completely blocked, so I'm not sure if there's really all that much trash in there.
Click to expand...

Unfortunately, that is not a good sign. An AC system must refer to the saying "cleanliness is next to godliness".

You should never see debris in the O tube. There are only 3 things I can think of that will cause dibris and they are all incredibly bad.

1. compressor failure
2. black death (Teflon coating sluff off should not be an issue in your case)
3. Desiccant bag exploding (usually due to wrong lubricant)

Any of the above requires a full system liquid flush and replacement of several components. receiver/dryer, O-tube, and usually the compressor. If you have a parallel flow condenser out in front of the radiator they can NOT be flushed, they must be replaced.

My guess is you did not get out all the junk from the first compressor failure. check that O-tube and if you have junk you need to do a full system flush (liquid) and as previously stated I would install a suction side filter.

Rufus
 
loudnslow said:
I definitely saw it go close to 450. How is this done? bypass? It didn't look like a connection to the coil.
Click to expand...

Usualy this as accomplished with a simple disconnect of the ground to the clutch coil. Some of the replacement compressors do not have a pressure switch in them and come from the factory with a slug in its place. you may not have one. If you don't have one, get one! They are required for a r134 a conversion.


Rufus
 
A LOT of wrong information here. Some good info too though.

You do NOT have to have the system running to charge through the high side.

This is the method I use to service MRAP's/HEMMTT's/HMMV's. I do this at least 2 or 3 times a week, so I know what works.

1- Evacuate old refrigerant. Make note of how much oil is removed.

2- Make repairs if needed.

3- Add oil- easy if you have an oil injector or Robinaire machine that does it for you. If you have one of these, oil gets added immediately after vacuuming. If you have neither, it has to be done before vacuuming. I usually just disconnect the low side line off the compressor and squirt the required amount into the hose. If you haven't flushed the system, only add what oil was removed. If none came out during evacuation, don't add any. This obviously doesn't apply if you've chemically flushed the system.

4- Vacuum for AT LEAST 30 min. 15 minutes is NOT enough. If it won't vacuum down to and hold at 29-30in HG, you have a leak. The longer you pull a vacuum, the more moisture is boiled off and the easier charging will be. On days where I'm not swamped, I'll let the vacuum go, then head to lunch, or go find something else to do. An hour or more works awesome.

5- Charge system. An MRAP calls for 7.05lbs of R134a. With a 30-45 min vacuum, I can usually get 4.5-5lbs into the system without it running, and both high and low side valves open. When it stops charging on its own, I close the high side valve and start the truck, let the compressor suck in the remaining charge.

6- Verify with thermometer that the system works like it should. With ambient temps above 100*, I can almost always get the temperature at the vent closest to the evaporator down around 45*. My record so far is 39*. :bow:


As far as trouble shooting your problem, I would say the condenser not getting adequate air flow or clogged with crap and needs cleaning. But you said the condenser is new. Is the condenser in front of the radiator? Is your radiator clean and bug/dirt free? Are you sure that your fan clutch is working correctly? Bottom line, the condenser absolutely MUST have good air flow, or the refrigerant just won't cool down enough, causing your high pressure. Do you have a fan on the condenser? If you can, point a big shop fan right at the condenser and see if your pressures drop. You can also pour some water on it to do the same thing. If your pressures drop, you have an air flow problem.

If the pressure went up as soon as the compressor kicked on then you have a restriction. If it came up to 400 after 20 or so seconds, then air flow is the problem.

How much refrigerant does the system call for and how much are you charging? Same thing with the oil. How much and what type does it call for and how much and what type are you using? It is VITAL that you get these right. To much oil and/or charge will both cause the problems you're seeing.
 
wasted wages said:
Ya think ??? :rolleyes::rolleyes::rolleyes::rolleyes::rolleyes: jeez....
Click to expand...
Not sure what you mean... I did run a vacuum after that too...


Looks like my problem was that I ended up with too much oil in the system. Taking a closer look today, if the engine was just idling, it ran fine. If I gave it a few blips of throttle, the pressure would start climbing on both sides. Sometimes it would clear up and come down, others I would run to 450 and shut off the compressor. I'm thinking that I was sometimes getting a stream of oil through the orifice effectively restricting it.
So took everything apart, flushed, put in correct amount of oil and freon - everything's back to normal.

Thanks.
 
It sounded like you had it oil slugged. Most new compressors are shipped with oil in them. So if you added oil it was likely too much.

Much of what Kid Jethro said works well. Especially the vacuum part. The longer the system is open the longer you want to vac it, and high humidity really makes that necessary. Higher than normal pressures on 1 side are usually a blockage. Both sides is an overcharge or over oiled. Other things could be the problem but thats where I'd start looking.

If the temp at the vents seems high and the system is working like it should then look for an air leak or or heater core water shutoff valve letting some water by. Some of the newer systems use a blend door to regulate the temp and those can get broken or stuck causing higher temp outputs than normal. An easy test is to clamp off the heater hoses and see if the vent temp drops. If it does you know where to go find the problem.

Hey Joe, on the MRAP's how many evaporators do they have? I ask because 7+ pounds is a big system. The trucks we do at work have 2 evaps and use between 3.5 and 3.75 pounds. My record so far is 40 degrees once. but lots of 43~46 degrees.
 
smalltruckbigcid said:
Hey Joe, on the MRAP's how many evaporators do they have? I ask because 7+ pounds is a big system. The trucks we do at work have 2 evaps and use between 3.5 and 3.75 pounds. My record so far is 40 degrees once. but lots of 43~46 degrees.
Click to expand...

They have one big ass evaporator and 2 big condensers. Both condensers have 2 fans on each that sound like jet's when they kick on. No stealth operations in an MRAP with the A/C on. :haha:
 
I know this is a very old thread, but it came up while researching my problem:

Restoring a 1994 GMC K1500 with 5.7 V/8. I installed virtually ALL new A/C system components, except the evaporator. I thoroughly flushed the evaporator, and pressure tested it for leaks. (None)

Vacuumed the system down for one hour plus, and then the system held the vacuum overnight with vacuum pump disconnected. I then started to charge the system as normal. Often times, if I work quickly, I can get enough freon into the system just from the vacuum, that the compressor will kick in and I don't need to bypass the pressure switch. In this case however, there was an electrical problem and the compressor didn't turn on. The system took a little under two cans on it's own, (about 20 ounces +/-) without the compressor running. Capacity is 32 oz. System calls for 8 oz total oil. New compressor came with 7 oz so I added 1 oz to new accumulator.

When I finished fussing with the electrical problem and got back to tending the gauges, things were all out of whack. The low side is pegged high, and when the compressor is on, the high side quickly (in about ~5 seconds) goes to emergency cut off at 450 psi plus, then the safety switch kicks in and turns the compressor off. Static, engine off pressures are Low side = pegged, High side = 125 psi.

What's wrong here, and what's the fix??? Help??!!

Thanks,
Vettepilot
 
What kind of orifice tube is in it? What is your "electrical problem"? You shouldn't ever have to bypass the pressure switch while charging. So you flushed the evap, to ensure no oil? What refrigerant are you charging with? If it's different than the one on the stickers, the charge listed doesn't apply. Pegged high pressure usually indicates a blockage.
 
Well, guess what. Even though I tried to buy quality parts, they're all made in China anyway, and the A/C lines at the condensor were a really, really poor alignment/fit. You know where this is going, huh? Yep, I accidentally swapped the lines at the condensor, right where the Orifice tube is located...

Embarrassing.

So, lines are swapped back and vacuuming back down for an hour or so again right now.

THANKS!
Vettepilot
 
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