AC system pressures - Toyota Nation Forum : Toyota Car and Truck Forums

murphymp · 11-09-2010, 10:52 PM

I've got a 94 camry w/ 250k miles. Been having AC trouble: cools great, no cool, totally random. After a lot of research, I replaced the expansion valve and receiver dryer. I then vacuumed the system and charged with 30oz r134.

The system seems to be cooling fine, but the system pressures don't match specs. The high side only registers about 150 PSI and the low side registers almost 40 PSI. Spec is 200-225 PSI on the high and 21-36 on the low. So the high pressure side is to low and the low pressure side is to high. WTF?

Any ideas of what's going on?

Stillrunning · 11-10-2010, 05:31 AM

Pressures relate to ambient temperature. Did you get the pressure from the temp/pressure chart? My FSM normal range is 21-35 low side, 199-227 high side - rpms at 1500, blower set to high, ambient at 85-95F. Your charge volume is Ok at 30oz as long as system was dead empty.

What temp are you getting from upper outlet vent with system not on recirc at what ambient? Too high on low side and too low on high side could be internal leak in compressor.

***Mister_Perkins*** · 11-10-2010, 09:12 AM

did you flush your coolant system out before charging it?

Or did you just suck the air out / recharge?

If you added oil to your system without flushing it you could have overfilled your oil. Even though you connect a vacuum pump to the system and draw the air out, you are not pulling the oil out.

Your system could be over filled.

Since your high side is low, It would indicate to me that your system is not pumping correctly. that would make your low side high.

NAPA sells an AC Flush solvent you may want to look into. Since our cars are old, the oils will turn into a gunk and clog the system , not allowing it to circulate properly

You could also get away with using ethyl alcohol for flushing

Stillrunning · 11-10-2010, 12:17 PM

Quote:

Originally Posted by Mister_Perkins

did you flush your coolant system out before charging it?

Why would he need to flush if system not contaminated with anything except moisture maybe? Excessive oil will reduce cooling but we don't know yet how the system is cooling. It's virtually impossible to flush through condenser and evaporator.

***Mister_Perkins*** · 11-10-2010, 12:37 PM

Quote:

Originally Posted by Stillrunning

Why would he need to flush if system not contaminated with anything except moisture maybe? Excessive oil will reduce cooling but we don't know yet how the system is cooling. It's virtually impossible to flush through condenser and evaporator.

he said that he vacuumed the system. A plugged Air conditioning line or pump would cause your high side to be low pressure and your low side to be high pressure. The car is a 94 so it was right in between R12 and R134. Depending on what oil was used in the compressor, mixing R134 oil with the R12 can clog the entire system (Causing it to have similar problems as listed that he is experiencing)

And when you flush the system, you pull your lines apart, clean each piece individually and re-install them.

The only other thing I can think of is if you push the AC button and your radiator fans dont turn on that could be the reason why it works sometimes and doesnt work other times

murphymp · 11-11-2010, 02:34 AM

System is factory r134 and used plain old r134 for the recharge. No system flush and no oil was added. Just pulled evaporator and replaced expansion valve and dryer. The specs came from the factory service manual. Ambient air temperature was about 75 degrees F today and I was getting a steady 42 degrees F from the center air vent. I checked again with RPMs of the engine at 1500. I didn't have the correct RPM yesterday.

The LP side fluctuated between 28-37 PSI and the HP side was between 200-225 PSI. There were bubbles in the sight glass when the pressure was dropping. I assume this was the expansion valve at work. I think the LP gauge may be reading a little high. I'll hook up my stand alone LP gauge tomorrow.

Is the pressure in the system supposed to fluctuate while it's running or is it supposed to be relatively constant? I've got swings of 10 PSI on the low side and 25 PSI on the high side.

Stillrunning · 11-11-2010, 06:01 AM

At least oil should have been added when you replaced the dryer. If the system had multiple leak downs and refills you should have also added some to account for leakage. Getting the correct amount of oil is an art and a guessing game. I've used an oil quantity measurement tool, but it is difficult to read and I don't use it anymore. There are specs for adding oil as components are replaced. The system fluctuates as the compressor cycles on and off, but when on, a properly operating system should not fluctuate (much). Using analog gauges will show no fluctuation, where as my digital gauges show slight fluctuations when compressor is on. I can't speak for the accuracy of your gauges, but 42 degree outlet air is pretty cold from the upper vent. You'll need a 95 degree day to really see how it operates. You'll also notice that the thermometer in the outlet vent goes up and down as the compressor cycles. You may still have air in the system, which means a leak. When you vac'd the system did you shut off the vac pump to see if the system held vacuum?

murphymp · 11-11-2010, 10:17 AM

I didn't add oil with the freon. However, I did add 1/2 oz (15ml) of pag46 oil to the dryer before I installed it as well as lubing the o-rings before reinstalling. I used a 30ml veterinary syringe which works pretty well. The manifold gauges and vacuum pump were loan-a-tools from autozone. Perhaps I will acquire my own set of gauges in the spring when things warm up here. It's not getting above 80 any more and probably won't till march.

The system didn't leak r134 at all before the expansion valve replacement. My cheapo low side pressure gauge always showed it was normal. I vacuumed the system for 3 or so hours and it held a vacuum overnight before I charged it.

I'm guessing I could have a failing compressor. Would there be a downside to just waiting for the thing to go kaput and then fix it? It looks like a replacement compressor is $150-200. To expensive for a shotgun fix.

hill8570 · 11-11-2010, 12:19 PM

If I had to guess, I'd say your expansion valve is opening up too far for the temp. Bulb might've been misplaced relative to the airflow, or it just might be a crappy expansion valve (even the OEM ones are touchy...if this isn't OEM, it's definitely suspect).

Stillrunning · 11-11-2010, 01:29 PM

The only restriction (variable) in the system is the expansion valve, that determines Hi/Lo pressures. Hill my be right about a bad expansion valve but with 250k on engine the compressor might also be internally worn. Cost wise I'd replace the expansion valve first, ya it's a pain to do all over again. Depending how long you'll keep this car and how the A/C performs at 90+F you may just want to live with it.

murphymp · 11-11-2010, 05:17 PM

Grrr... Toyota dealer wanted $90 for an expansion valve. I got one and the receiver/drier via rockauto for $40 delivered. At this point I think I'll wait till it heats up in the spring and see how it runs. We've had a couple of near 80 degree days and it's been cooling just fine for about 200 miles. The random stop and start problem has not reoccurred, so I think I got the culprit. This was the thread that helped me identify the the original problem as the expansion valve since I was having the exact same symptoms.

AC Intermittent, Can't we solve this?

Yea, getting the evaporator out was a super big PITA. I don't want to do that again unless I have to. Nothing like working practically upside down with my head on the passenger floorboard. I'd venture a compressor swap would be easier. I'll live with it for now and see how it goes. Thanks for all the help.

hill8570 · 11-11-2010, 06:39 PM

Quote:

Originally Posted by murphymp

Grrr... Toyota dealer wanted $90 for an expansion valve. I got one and the receiver/drier via rockauto for $40 delivered. At this point I think I'll wait till it heats up in the spring and see how it runs. We've had a couple of near 80 degree days and it's been cooling just fine for about 200 miles. The random stop and start problem has not reoccurred, so I think I got the culprit. This was the thread that helped me identify the the original problem as the expansion valve since I was having the exact same symptoms.

AC Intermittent, Can't we solve this?

Yea, getting the evaporator out was a super big PITA. I don't want to do that again unless I have to. Nothing like working practically upside down with my head on the passenger floorboard. I'd venture a compressor swap would be easier. I'll live with it for now and see how it goes. Thanks for all the help.

Yeah, the OEM expansion valves are pretty spendy, but you can pick 'em up for ~$60 shipped at the cheaper online stealerships. Given it helps to be a three-handed double-jointed midget to be able to get that damn evaporator out, I'd rather spend money for OEM. Biggest problem with a expansion valve being too open (other than freezing up the evaporator and snowflakes in the car) is that your hi-side pressure never gets high enough to let the compressor cycle off -- not a good thing in the long run. Did you put the expansion valve bulb back on the same spot it was originally? Put it in the wrong spot and it'll be seeing a too-hot temp, and cause the expansion valve to open too much.

murphymp · 11-11-2010, 10:09 PM

I'm 6'5", no midget here! I did check it again today and the compressor is cycling on and off at 1500 RPM.

My expansion valve looks like this:

I don't know anything about a bulb. Perhaps you're referring to a different style? It only goes on one way.

I got out my old one and looked at it again. I wonder if it might have been clogged? There was a small amount of black junk in the area with the pinhole. I wonder if this could have caused my problem.