AC issue, shared in hopes it will help others

My son's 89 F350 has about 50 psi static, which is low for 90F, but we noticed something odd right away on filling it so stopped after four oz of oil/dye and one can of R134.

The oddity is identical pressure readings on the low side and high side with the compressor clutch jumped to run. This condition can be caused by an blown out orifice tube.  We had drawn the system down for about 30 minutes so moisture in there should be minimal, otherwise that can cause elevated low side pressure. It held the vacuum successfully. So the system has no leaks, at least no big leaks.

Following up on the orifice tube lead, I checked on Rick's Free Auto Repair I see that all F-series from 1980 to 2009 use orifice tube. Whew.

So that's what we'll replace.  And a receiver dryer for good measure. The system was open for a few hours and it's been humid in Texas.

AC work is not all that hard so I encourage folks to try. Shops charge over $100 just to service an AC. It can be done at home.  Just get you some gauges and manifold, some cans of R134, some dye/oil, and crack the books. I even repaired the AC in my Cummins 4BT grader last summer.

FYI

Appreciate the symptom and resolution heads up

Yes, thanks for the heads-up.  Please let us know what you find.

Yep, working on my AC right now. Fixing to head out there and put a charge on it. I have concerns that my compressor may be worn out, so we shall see!

 

Same or close pressures can also indicate a bad compressor.

Yep!  But that compressor just came out of a truck with a blown motor, featured in another thread. It was working fine there.

A few R134 cans. Fleabay had the best price.
A set of gauges with manifold. I used Harbor Freight.
Decent vacuum pump. HF again for me.
Small doohickey to add dye/oil. Went with best Amazon reviews.
64 pz of dye/oil, got it on fleabay.
Assorted spare fittings from fleabay.

That's all you need!

Our orifice tube is on order and we'll keep y'all posted. It's HOT in Texas these days.

RenoHuskerDu wrote

Yep!  But that compressor just came out of a truck with a blown motor, featured in another thread. It was working fine there.

Ok, cool! (Pun intended!). Good you know the history. I didn’t remember if you knew.

RenoHuskerDu wrote

A few R134 cans. Fleabay had the best price.
A set of gauges with manifold. I used Harbor Freight.
Decent vacuum pump. HF again for me.
Small doohickey to add dye/oil. Went with best Amazon reviews.
64 pz of dye/oil, got it on fleabay.
Assorted spare fittings from fleabay.

That's all you need!

Our orifice tube is on order and we'll keep y'all posted. It's HOT in Texas these days.

Great write-up and really appreciated the part & equipment list.

This is another To-Do item on my list (original factory air system).
And especially with more "Heat Domes" in our future! Current Heat Dome is forecasted to last another 4 or 5 days.

If you are doing the work I strongly suggest running some AC flush through the system with the orifice tube removed.  Get as much of the old oil out as you can and then add the proper charge of Pag oil for your system.  If you do this you will actually notice a improvement in the AC cooling.  Oil doesnt cool and for some strange reason in the old days shade trees would add a can of oil when ever they would add refrigerant citing that oil flows with the refrigerant and will come out with the refrigerant.  Problem is they are adding more than the miniscule amount that will seep out with the refrigerant and then you end up with a high head pressure situation where there is horrible cooling but the pressures read good.

Im going to be doing this for my truck if I can get the clamp on hoses off my receiver drier (dealer AC unit).  I currently blow 58 on a 100 degree day but I want to get it right.  The other car of mine I did it on I flushed it as I had a compressor lock up (was put in new about 8 years ago) head pressures are identical to what it was before with the new compressor but the AC blows so much colder than it did before.  I suspect too much oil in the system from the previous people that worked on it.

I also suggest looking at pag oil with the UV dye already mixed in.  I picked up a large bottle of the stuff for $5 and its enough to do all my vehicles multiple times.

Rick - thanks for "the devil is in the details" post ....

Pag, what is that? Time to do some Internet research.

Found out that Pag stands for Polyalkylene Glycol, (PAG), a synthetic lubricant that is used in combination with a refrigerant that replaces CFC-12 (R-12) refrigerant in air compressors (which actually don’t compress “air” at all). So, then why do they call air compressors air compressors? Ahhh…. that’s for anohter time, don’t want to get sidetracked.

Further research reveals a whole bunch of different compressor gasses, lubricants, and problmes with seals, O-rings, and other stuff. Compatibility charts are lengthy, even for Ford, according to “Article No 98-4-8 Air Conditioning R-12 to R-134a Retrofit Kit Availability - Vehicles with factory installed A/C only”. Mix things up and there can be problems.

Will an '85 A/C unit have to be changed out? or rebuilt? What oil goes with what A/C system? This is (for me) getting a bit complicated. Doing the physical work is one thing, but making sure the right chemical stuff is used is another. Actually, its quickly becoming the hardest part.
-= John =-

Nemesis F150 wrote

Rick - thanks for "the devil is in the details" post ....

Pag, what is that? Time to do some Internet research.

Found out that Pag stands for Polyalkylene Glycol, (PAG), a synthetic lubricant that is used in combination with a refrigerant that replaces CFC-12 (R-12) refrigerant in air compressors (which actually don’t compress “air” at all). So, then why do they call air compressors air compressors? Ahhh…. that’s for anohter time, don’t want to get sidetracked.

Further research reveals a whole bunch of different compressor gasses, lubricants, and problmes with seals, O-rings, and other stuff. Compatibility charts are lengthy, even for Ford, according to “Article No 98-4-8 Air Conditioning R-12 to R-134a Retrofit Kit Availability - Vehicles with factory installed A/C only”. Mix things up and there can be problems.

Will an '85 A/C unit have to be changed out? or rebuilt? What oil goes with what A/C system? This is (for me) getting a bit complicated. Doing the physical work is one thing, but making sure the right chemical stuff is used is another. Actually, its quickly becoming the hardest part.
-= John =-

Honestly Ive always just flushed the old oil out and run PAG oil.  Never had a problem doing that before.  Many claim it poses a problem but Ive never seen a problem in 20 years of doing it this way.  The question how ever is which PAG to get you have many grades and I typically run PAG 46 but Ive seen PAG 120 before.  In the case of my '82 truck, thats a york compressor for a dealer AC installed unit, when I get around to flushing the system out I will run PAG 46 just the same as most of the oil will remain in the compressor`s sump to lubricate the compressor.

With a rotary compressor Ive heard some compressors will make noise with thinner PAG oil and call specifically for a heavier PAG oil.

Besides what type of PAG oil to use is how much total?

Then a break down how much in each part:
Condenser
Compressor
Dryer,
Evap coil
and if any for hoses?

When I was rebuilding my system I had a vary hard time finding anything on how much per part, all mine other than the evap coil was new.
Yes the coil was flushed out and think I used PAG 46, would need to find the bottle to make sure.
Dave ----

I just finished this up last weekend. I kept my OEM FS6 compressor, but had concerns about it due to it's seemingly lack of suction when I turned the hub. Still not sure that it isn't wore out. I replaced all the refrigerant lines with the exception of the suction line. Replaced the evaporator, dryer, orifice tube and installed all new O rings. I kept my OEM evaporator and flushed, along with my suction line, with brake cleaner. I pulled a vacuum of about an hour and let it sit over night to find that it held. I pulled another vacuum of about 45 minutes a little before I charged the system.

Prior to assembly of the system, I put 10oz of PAG46 oil in the system. Five ounces went into the compressor and the remaining 5 oz was put in the evaporator, condenser and dryer.

There is a formula for conversion of R12 to R134. The R12 system takes 52 oz. Conversion to 134, per calculations, was 42.8 oz. This amount is by weight, not volume. I went just a little above the 42.8 oz calculations despite having a scale.

My final high side and low side readings are shown in the photo, as is the cooling temperature in the vent. Both high side and low side are high and the best idling temperature I got was 70 degrees. Temperature outside this day was 98 degrees. Driving, I got a temperature of 60 degrees. I'd like cooler and I believe it was cooler when I had it converted over all those years ago. I'll be monitoring it. I've only driven it once since doing the job but will be monitoring as the ambient temperature drops.

"Replaced the evaporator, dryer, orifice tube and installed all new O rings. I kept my OEM evaporator and flushed..."

I'm in a similar pickle. See my next post. But please clarify if you replaced the evaporator or just flushed it.

Well, so far no success. I'm looking for a good auto AC forum now. Anybody know of one?

We installed a new receiver/dryer and orifice tube. After taking less than half a can of R134, I noticed that high and low sides were still virtually in sync. So we stopped adding R134 and looked for leaks. It was dark so our silly little "black light" flashlight actually worked a bit. We found one missing O-ring and replaced it.  But in the morning, pressure was all gone.

Next steps:
1) get a more powerful black light today at NAPA
2) order AC 270-piece O-ring set, then renew all in system
3) pull new R/D out now and cap it up (humid lately, rain coming)
4) pull and inspect evaporator for evidence of leaks
5) ditto for condenser
6) did I miss anything?

I tend to suspect the donor compressor too now.  Anybody know diagnostic steps? Put a vacuum gauge on the low side?

Although I don't fully understand this mode of failure, I've read that a failing compressor can cause high and low pressures to be the same. I suppose that's caused by internal seals failing. Yes, this compressor came from a working AC system in an 89 Bricky, but it never was all that cool, and it sat for 6 months after the cylinder jacket perforation event late last year.

John - My temps were colder than that with similar pressures - before the leak I can't find took away the refrigerant and the pressures dropped.  So I'd say you have a problem.

Reno - Sorry you are having these problems.  Hope you get it sorted soon.

I don't have any guidance for either of you.  I've given up and am taking Big Blue to a pro on Monday.

RenoHuskerDu wrote

"Replaced the evaporator, dryer, orifice tube and installed all new O rings. I kept my OEM evaporator and flushed..."

I'm in a similar pickle. See my next post. But please clarify if you replaced the evaporator or just flushed it.

I kept my evaporator and merely flushed it. If your pressures are equal, I'm thinking your compressor may have an issue.

Here's a forum for where I've spent a little time: https://autoacforum.com/

Gary, it's really hard to say as I did all this in near 100 degree heat and high humidity. When I drove it, it was very hot and it came down to 60. But like I said, I do have concerns about my compressor. I know more in the weeks to come.    

Granted it is only 84 degrees today, but I put another can of R134a in so I could test and got these readings:

Engine RPM: 1500
Low: 35 psi  High 250 psi.
Outlet air temp in the passenger's left vent:

Doors open and in Normal: 62

Doors closed and in Normal: 59

Doors closed and in Max: 47

Note that this wasn't really a fair test because at about the time I shifted from Normal to Max I heard the belt-driven fan come on and that took the outlet temp south pretty quickly.  I think the doors closed/Normal temp reading might have been lower if I'd waited before switching to Max, but after closing the heater valve and cooling the heater core down it would have taken quite a while for it to heat back up, so I didn't wait.

And there was almost a steady stream of condensate hitting the pavement.  Plus the receiver/dryer was wet as were some of the metal lines.  It cools well if I could just keep the refrigerant in it.  

I also just flushed the evap coil and everything else was new.

You guys that cant keep psi in the system how long did you pull a vacuum and how long did it hold after you turned the pump off?

I also had growing pains with my AC system.
It held a vacuum for and hour before I started filling it.
First pain was a bad new O-ring that lost the psi in a week IIRC.
A little bit after replacing O-ring I must have for got to tighten the fitting and lost everything again.

The other day OAT was 97* heat index was 107* to 110*
It does cool the truck off but I think it could be better.
I took the temp prob out of the truck months ago so dont know what it was blowing temp wise.
If I came to a light and the RPM dropped to an idle it would start to blow warm but still cooler than the OAT LOL.

I can not run MAX AC as every little hill I come to it would go to defrost till I let off the gas.
On normal AC it only did it if I was really on the gas or climbing a good size hill.
When it gets a little cooler I need to look into this as it is a PITA!

Good luck on fixing your AC's
Dave ----