93 toyota pickup, low side good, high side climbing

[bohica2xo]

That condenser is not performing well at all.

Airflow is obviously part of it - that fan begins to slip pretty good by 1800 rpm, looking at your numbers.

But the water spray should have pulled it below specs. At 86f with a wet condenser I would have expected a high side around 200 or even less with a lot of water.


I am beginning to suspect that condenser. It looked like simple airflow, but with all of the bypassing corrected those pressures are too high for just the weak fan clutch.

[Djea3]

In my most recent numbers I did NOT use any water on the condenser. In the past I have sp;ashed water on the condenser and saw immediate reaction, but there will not be water available when driving. there is an instant reaction so no need to check farther.

I did not see the compressor cycle at all....with 25lb low and going to 400 lb shouldn't the pressure switch have activated and shut the compresser? I cant find the specs anywhere.
does anyone have anything negative abt uac components??

what next? what could cause a new compressor that is otherwise good not to function? what else could cause these symptoms?

[JohnHere]

I don't think you answered a key question bohica2xo asked earlier: Your truck came from the factory with R-12. Is it still R-12, or was it converted to R-134a at some point? If it's still an original-spec system, my references for this vehicle call for 29 ounces of R-12 and 7 ounces of mineral oil. Does your under-hood decal agree with that spec?

If it was properly converted, you would need to charge it now to approximately 80 percent of the original spec, or about 24 ounces of R-134a. In addition, the mineral oil must have been completely removed and replaced with 7 ounces of PAG-46. I'd put 4-1/2 ounces in the compressor, 1 ounce each in the condenser and evaporator, and 1/2 ounce in the R/D. One ounce more oil distributed throughout the system would be okay, too. Many Toyota A/C systems of the late-1990's running R-134a call for 8 ounces of PAG-46.

You also didn't specifically mention how you evacuated and charged it, and with what.

Lastly, if it was converted, the new receiver/dryer must be compatible with R-134a.

[Djea3]

Ok here we go. I used these UAC part numbers from rock auto kit:
UAC KT3742A
UAC CN3932PFC
UAC CO21008C
UAC EX7012FC
UAC RD1224C
UAC RS2581
UAC RO0900B
Then when this problem occurred I changed the TX valve: Napa 207306 which shows for 1994 so IS a 134a part number.

I checked the specs for the fan clutch. It is about a 1.4 ratio to the crank. At cold start up it is a little over 70% of calculated fan shaft speed at high idle. When warm it can be as low as 20% shaft speed. Therefore all the numbers seem to work and 640 at warm idle is actually on the high side. 750*1.4*.7=735 for cold idle at 750 rpm. 635 should be well within spec unless I don't have all the information. Does the fan clutch hold 1:1 at 750 or does it slip at warm idle? Hot at 1800 engine RPM should can be as low as 500 rpm so the numbers I gave before do not seem out of line. Remember that the clutch is designed for rpm when DRIVING not sitting. Regardless.....the ac system was running acceptably before replacing parts.

This truck has been 134a for MANY MANY years. I also flushed EVERYTHING except the new parts. The condenser was pressurized when it arrived.

So where are we now?

[bohica2xo]

So the truck is a 134a CONVERSION. Ok. We will circle back to that in a minute.

You replaced a leaking compressor, and your assertion is that "worked fine before". Did you test the systemm pressures before the repair?

Perhaps the old compressor was not able to post pressures above 300 anymore?

So you replaced the parts, cleaned things and you see high pressures.

When we see this it is usually a condensing problem. Airflow across the condenser is the #1 culprit. So we use water to find this problem quickly. Yes, we all know you can't carry a hose - this is the purpose of the FAN. Again the #1 culprit is a dead fan clutch. #2 is missing seals allowing bypassing of the condenser.

Every mechanic has had a part fail while working on a related item. It is entirely possible that right about the time you replaced a tired compressor, that the fan clutch was sliding down a steep failure slope.

You are cherry picking some book values to support your position that the fan is doing it's job. On what planet would a fan speed go DOWN as heat load increases? That 20% value reflects a situation where the working fluid in the clutch is warm, and the heat load is LOW. At high heat loads the clutch is supposed to couple more securely, and increase fan speed.

Tim is spot on, here in the desert we used to lock those old Toyota fans because they were barely adequate in costal california. I still hear them on the street when the landscapers go by.

Now, the 134a conversion. When properly converted a system was supposed to have an HPCO installed in the clutch circuit. They cut out around 425 PSI, and reset around 350. There is still a HPRV in the system, and most of those open around 450 psi. This is the big reason to shut down a system at 400. A slightly weak, corroded HPRV may open at a lower pressure, and they often will not reset. I try to avoid opening that drawer on Pandora's dresser.
Does your system HAVE an HPCO?

Back when conversions were more common, the plan was to charge 85% of the R12 charge by weight - to control the high pressure issues people were encountering during conversion.

An overcharge will certainly give poor performance, and high pressures that you can control with a garden hose.

About serpentine condensers.
Serpentine condensers are made by extruding an aluminum shape with a core of multiple passages. While the racetrack outside shape, and (usually) triangular inner passages exist in the basic extrusion, they are not finished size. The extrusion is stretched, and the cross section shrinks to the size required - like stretching a rubber band, it all gets smaller than it was when extruded. And they stretch it a lot. As much as a 50% reduction in area. Then it gets bent in to the repetitive "S" curves, fins brazed in between etc.

So as you can see there are a few ways for things to go wrong, but add in a 3rd party making parts for a 25 year old vehicle in a country that has very little A/C experience. What happens if the manufacturer figures out they can stretch the extrusion a little more, getting more parts per ton of Aluminum? The tube is 0.75mm smaller both ways, the walls thinner, and the passage ways a little smaller. The interior volume just went DOWN. It may cool as well, but add a couple of ounces too much & it is overcharged.

1) Your pressures are too high.

2) Your airflow sucks.

3) You may be overcharged.

4) Your aftermarket condenser may have a blocked channel or two right from the factory.



So to avoid chasing your tail, and belt feeding parts in to a vehicle I would suggest fixing the obvious, and recovering & adjusting the charge level. If none of that improves things then a condenser swap is next on the list.

[Djea3]

Thank you for the full explanation. I did not cherry pick any information, using only that which was available...the 70% value is supposedly the highest RPM for a standard duty thermal clutch so the math works. However I will bow to your experience and go ahead and freeze up the clutch and try again. This should eliminate at least one variable, unless the fan is weak as well.

HPCO, where would they locate it in a conversion? The OEM was a low/high pressure switch and located in the box under the dash. As to the seals between the condenser and its mounting frame I used standard weather stripping as I had it on hand. It there a kit for this or better way?

I will begin to lock the fan tomorrow and we will see what happens then and will post.

Thank you very much for such a well thought out answer that is logical. Your input at least assures me doing this is the right thing. This vehicle was in Dallas TX forever and now in Tampa. While they get hotter we get humid, it makes sense that the lower density and lower heat transfer values from humidity could make a difference in the cooling especially if the clutch is weak.

Thanks again!

[Tim]

Just for information. The UAC condenser used in replacement is a serpentine model, not a PFC.

http://www.ackits.com/toy-pu-94-89-4592 ... %203932PFC

[bohica2xo]

The HPCO for a retrofit is a Tee fitting for the high side adapter:

http://www.ackits.com/r134a-retrofit-sw ... 20retrofit

This gives a service port & a cutout switch. The switch is just wired in series with the clutch, it is normally closed. Not very esoteric, but they can save a lot of headaches.

For weather stripping almost anything works, as long as it stays put. Adhesive backed foam strip from Home Depot has fixed a lot of Suburbans over the years. Go a little thick on the foam so it is clamped between the condenser & the core support.

Humidity is a big load on a system, the heat capacity of the air at 50% vs 10%. Hope this helps.

[Djea3]

UPDATE: Took a rain day. I purchased some 5000scf (3000 up to 6000 is spec from Toyota) silicone from a hobby shop and rebuilt the fan clutch today with 50cc per spec as the bearings are fine. I reinstalled the fan and tested it, definitely higher output of air and higher rpm. 1000 rpm fan at idle, 2000 rpm fan at 1750. I decided that the system needed a little more 134 added it. Here are the results:

Fully warmed up engine. 86 degree ambient, 66% humidity all tests. Idle 860-900, high idle test 1800-1900 rpm

Idle : cycling (relatively slowly) between 40/325 and 30/425, vent 45 degrees
high idle cycling (4 to 7 seconds) between 40/315 and 20/415, vent 40 degrees

Then I used water on condenser tried to make it slow and constant.
Idle 35/325
high idle 20/325

The dryer seems to be about 10 degrees hotter than the bottom of the condenser in all tests. The HP lines from the dryer are same temp as the bottom of the condenser.

So it seems as if my pressures are still low/high regardless of the condition should be 50/240 ish according to the temperatures outside. I have already replaced the tx valve twice.

What the H is happening?

[Djea3]

PS: I just found this chart (hope it posts). It is relative humidity temperature service port pressure chart.

Interpolating it we should find a little different than I expected:
45-50 low side, 365/380 high side at 86 degrees 66% humidity. I feel better, however something is still not right.

post-13500-0-74080200-1408068036.jpg (142.39 KiB) Viewed 7757 times

What now?