What would cause very low pressure differential between high and low sides, OTHER than the compressor?

After evacuation, the system will accept only half a can of charge, and pressure differential is ~ 85psi/140psi. Had similar problems with my last compressor, but that one squealed like a **** - I found worn side housings and a lot of heat spotting inside that old compressor. New one turns easily, and I decreased belt tension a little.

I have an expansion valve on order from Malloy... Everything I've read tells me this won't help, but it's cheap to replace anyways.

Any ideas? No A/C in Texas weather got really old, really fast.

 

check to make sure you have no leaks in any of the lines, condensor, drier and even under the dash parts.

make absolutely sure that you have ZERO leaks

 

What temp and humidity were these pressures read at? Sounds like the second compressor is bad as well.

 

Is the compressor clutch slipping? or belt slipping possibly?

 

As far as things under the hood, there are no leaks. I have checked this multiple times over. Have not checked evaporator and expansion valve, will do when the new valve gets here.

~ 96F, 40-46% It is barely compressing above static pressure. I'm really hoping this second compressor isn't also bad, which is why I want to explore the other possibilities of what it could be. But, if that's what it comes down to, it is what it is.

No to both.

 

How long does the compressor run? With only half a can I would guess it has a high cycle rate. If it has a normal cycle rate the comp. is bad. If it has a high cycle rate, you need to get more freon in and retest.

 

Continuously. A friend was loading in the freon while I was keeping RPM around 2000-2500. He has recharged the system in his FD as well as the cars of many other people here in Houston, so I trust him to not be doing anything incorrectly.

I would put more than one can in, but it will not accept more refrigerant without the low side skyrocketing. Maybe I should give it another shot.

 

Overcharging will cause a high low side, but the high side is low for your conditions as well. I would evac. the system and verify the charge weight, but I think your going to find the comp. has valve sealing issues.

 

I might as well wait until the new expansion valve gets here next week then. I will update this thread with the results.

 

An expansion valve that is failed wide open will produce the effects you describe. I would be surprised if you have two bad compressors; these rotary vane compressors will usually work (albeit noisily) until they literally fall apart.

You won't be able to charge refrigerant into the system unless you can get the low side (suction pressure) << vapor pressure of the refrigerant you are using.

 

I thought it was the expansion valve as well. It makes sense to me, because even if it is stuck wide open, there is a very small amount of restriction. That would explain the low pressure differential. While it is low, there is still a small amount of compression; if the compressor were bad, I would think there is no pressure differential. But, can't rule that out unless the expansion valve I ordered fixes the issue.

I understand that the system will not charge unless the low side is at a lower pressure than the fluid in the can. I would have failed thermodynamics if I didn't. The compressor is creating at least some vacuum on the low side, so I thought maybe after letting the oil seep into the o-rings, I would give it another shot.

I'll update the thread again once I get that expansion valve. Just a little info for anyone else that orders one: the part number in the '94 parts manual for MANA A/C is NLA (this would be for '94-'95 cars). Ray is sending me the '93-'94 MANA expansion valve, which should be fine. He did not send me a P/N, sorry.

 

I would suspect the expansion valve as well since your low side is high. If your low side was low, and your high side was 140-ish

If you have R-12 the 1993-1994 part number should work. If you have an R-134a system (and I've yet to see a MANA R-134a system on a 1994) then you may have issues with the threads being different, but not to worry, the MANA system uses a generic externally equalized TXV design. Find one at the Auto A/C supply house with the right threads and fittings and you're in business.

I would suggest you not run the system above idle until you have most of the charge in the system. It should pull most of it in before you need to increase the engine speed. With a partial charge, you're not getting proper oil return to the compressor, so the fewer RPMs the better.

When I charged my system I put nearly a whole can in as a liquid on the high side before starting the car. It was funny to see all that pressure twirling the compressor backwards as the refrigerant migrated to the low side of the system.

 

Car is a '95 with R-134a, so it sounds like it won't fit. Eh, I'll have to see. If it does not work, I'll check the place you suggested.

The car was not run above idle for very long, and I have long since disconnected the clutch for the compressor.

 

For any one wondering, FD01-61-J14 (expansion valve) does fit on my 1995 with MANA AC. FD01-61-J14 and the O-ring for the expansion valve (H261-61-J17) is $88.71 shipped in the continental US.

However, this still did not help my AC issues. There are two more things I have not replaced - the condensor and the dryer. The high side condensor line is slightly crimped, but my friend cewrx7r1 said he has a worse crimp in his and his AC still works. We're thinking maybe the condensor or dryer are gunked up pretty bad, but still flow well enough to allow some flow. Going to try to source a condensor. Can get a dryer locally. Or maybe have someone make a custom condensor.

Ryan1 - not ruling out the compressor, just trying to eliminate less costly items first. The condensor and dryer also happen to be the two components I have not replaced.

We have verified that all the LINES flow fine. Also verified that the system does not leak over the course of 2 days, so there are still no leaks.

 

Maybe someone put some stop leak and it encountered moisture in the lines and gunked them up. Not sure of the effects you might see but I imagine you wouldn't be able to get much charge into the system.

 

Interesting.

The drier should be replaced if the system has been open for any length of time, and especially if it is the original one.

Where, locally, are you buying a MANA drier from? I'm about to take my system down to replace the compressor and I'm gonna replace mine again. Last time I had to order it, and the company that made 'em didn't do a great job machining the holes where the o-rings go. It is leaking ever so slightly.

If there's a restriction somewhere on the high side, it'll usually show up as a cold spot since the restriction acts exactly like an expansion device.

Exactly what are your high and low side pressures? You stated you had a differential of 85/140....implying that the difference between high and low are 85-140.

BTW, I'm local if you want another set of eyes to look at it.

 

OP: Steps to take when recharging or replacing a/c equipment:

1) Vacuum system - evacuate all old refrigerant and oil.
2) Replace drier unit if system is opened
3) Once everything is replaced, vacuum system out and do leak test by using vacuum hold on A/C equipment.
4) Check to see that system holds vacuum, if not, you have a leak. (check for faulty equipment or o-rings)
5) Using a/c equipment, recharge system with refrigerant and correct oil (usually PAG)
6) Run system to check operation.

 

Very likely the issue.

Getting a dryer from Oreilly, then using the old drier to make a bracket for the new one. I read a thread on here that stated that the dryer they sell there has the correct size fittings.

I'm really hoping it's not the compressor, which is why I will try cleaning out the condensor in addition to replacing the dryer.

Ok. What I've been saying is that the low side is at ~85, high side ~145. If you are asking about the difference in pressures between both sides, then it is anywhere between 55-75psi. Not much. The lowest I have seen the low side reach is 80psi.

You're welcome to come look at it when I go to Chuck W's place to do all this stuff (on Friday after I get off of work, so I'd be at his place ~6:30-6:45).

Thanks, if you actually read my thread, you would see that I had done all of this with the exception of replacing the dryer.

 

Oh, I'm out in Katy too man. But I'll be using this thread to do all my checks when I change out my compressor next month some time. I hope you get it figured out, I know what driving around here is like without a/c...

 

It doesn't appear you did.

I read your thread, that is why I wrote in to help. There is no mention of an actual A/C evacuation/vacuum/replacment machine anywhere in your thread, by that I mean, an actual, professional machine. By the way your thread reads, you are using hand/home tools to recharge your A/C. This almost always leads to FAIL. Nowhere in your thread did you state that you did a vacuum hold test using said machine, this would show you that you have a definite leak, instead of wondering... do I have a leak?

You also stated that you were running the compressor while adding refrigerant. A professional machine does not require the car to be running, actually, it requires it NOT to be running.

So, the question remains, (and judging by your thread you are not using a machine)... are you using a professional machine or are you trying to do this at home using cans of refrigerant you bought at O'Reilly's or Autozone to recharge your A/C?

 

No, I'm not using a machine, but I am using a pump to pull a vacuum on the system greater than 25 inHG. The system has held this vacuum for days on end, hence why I never once asked "Do I have a leak?..."

We let the vacuum pull in as much fluid as it can (and obviously, the gas in the can expands into the system until pressure in the system reaches the static pressure in the can - about 110psi in this weather). Then the car gets turned on to allow the compressor to draw in more fluid. It's not like I'm just sticking a can on the car without evacuating my system first...

Doing it this way has worked for the person who's helping me for as long as he's had his car (single-owner R1). He's recharged twice from what I remember, same old drier. Works better than the AC in my DD (1997 Mercedes C280).


I reread my own thread, you are right, it was never mentioned. My bad on that. Thanks for helping and pointing it out. My apologies for being hostile.

In the meantime, I have purchased the proper AC cleaning fluid as well as new PAG 100 oil. Will be cleaning the condensor and replacing the drier this Friday. Then PULLING A >25inHG VACUUM, leak testing, etc.

P.S. I have had 3 separate bad experiences bringing this car to a "professional" shop here in Katy and Houston. Unless the shop wants to let me use their equipment, this car is never going to another shop again. Too many incompetent or lazy "certified" technicians here.

 

This thread? As far as I know, that dryer is NLA, and even if it wasn't the fitment is poor at best....mine has a slooooow leak.

If the low side is still that high then you still have an expansion valve problem, or by some miracle you've managed to create a huge plumbing problem that bypasses the expansion valve.

I suspect I know what your problem is.... Tell me, what did you do with the bulb on the TXV?

 

It doesn't require a professional machine. Just a good vacuum pump, guages and the right procedures.

 

Zip-tied and taped it back to the evaporator line, the same way that it had been when I took it out. Not insulated tape though, it's bubble-gum tape (think that's what it's called).

It could still be a huge plumbing problem. And it would be better to be safe than sorry, so even if the TXV is the issue still, I'm going to clean the condensor and replace the drier. Just a good idea, especially since I have most of the stuff already lol.

Sucks to hear about the fitment issues though. No, it was not that thread, I'll have to ask Chuck to send it to me again. Or tell him to come post it. Anyways, it's not NLA on O'Reilly's site... or Autozone's. I'll go to the store and check tonight.

I would think it's better to have a drier that leaks veeeery slowly and does it's job well rather than have one that's probably fragmenting on the inside and not allowing that stuff to escape the system lol. How slow of a leak are we talking about.

Thanks.

 

It is best for the line it attaches to to be perfectly clean, and then the whole thing well insulated...but if it is attached, it shouldn't be as far off as what you're seeing. The pressures you're seeing can be a result of a bulb that isn't correctly attached.


Just make sure you get all the solvent out of the condenser. It is a *bitch* to flush parallel flow condensers.

If you're referring to the "Murray" drier listed on O'Reilly's site (part# 33592), that's for the Nippondenso system.

My electronic sniffer won't catch the leak, but after 7 months it is a little oily on top.