R-134a - high side 450, too high?

[sasilverbullet]

Just put a new compressor/rcvr dryer on a 90 Grand Marquis. Filled it up with the required oil first, then put two more cans of 134a in. Cools just fine but the high side is running around 400-450. Keep in mind that's at 99 degrees ambient with 90% humidity and the car standing still w/engine about 1500 rpm.

Is this too high? If so, any possible causes? Bad compressor?

 

[EricF]

plugged orifice tube..
cooling fan not pulling enough air through the condenser...
(so bad fan clutch or electric fan not spinning at speed.)

 

[cmf]

It should be around 315-325 on the high side at that ambient temperature. Are you idling it and not using recirculation? That can cause issues because it will suck in the hotter than ambient temperature engine air. I always charge cars with the AC on recirculation with the windows open, so it's sucking in close to ambient temperature air.

 

[Trav]

Way too high, not far of blowing something if left this way. It should be around 225-250psi at those temps.
Is the fan working? Check the clutch on the fan if it has one.
You say you put 2 cans in, how big were the cans and how much does the system hold?
Did you vac it down?

For vehicles currently running with freon R-134a only
Outside-----low side-------High side------Center vent temp
60 F -----28-38 psi----130-190 psi ----44-46 F
70 F ------30-40 psi ---190-220 psi ----44-48 F
80 F ------30-40 psi ---190-220 psi ----43-48 F
90 F ------35-40 psi ---190-225 psi ----44-50 F
100 F -----40-50 psi ---200-250 psi ----52-60 F
110 F -----50-60 psi ---250-300 psi ----68-74 F
120 F -----55-65 psi ---320-350 psi ----70-75 F

 

[cmf]

250 at 1,500 RPM? I could imagine 250 at idle RPM but not at 1,500 with 99 degree ambient temperature. Correct me if I'm wrong.

 

[Trav]

From this article...
You can also use this good rule of thumb with R134a, run fan on High with all windows open and engine at 1500 rpm. High side pressure in PSI should be about 2.2 to 2.5 times outside air temperature in degrees F. Example if it's 90 degrees F, high side should be no higher than 225PSI

http://www.instructables.com/id/How-to-Repair-Automotive-AC/step1/freon-check/

 

[cmf]

Weird, my chart must be wrong then. Here is a picture of it, it's for 1,500 RPM:

 

[Trav]

That's strange alright, the chart that came with my robinair gauges is close to the one in the article @1500 RPM. But that could just as easily be wrong also.
I always went by it and never had one go much over 250PSI but who knows.
Maybe someone who works a lot with A/C can chime in.

OP is this a R134 conversion? If so i read somewhere there needs to be something changed not just the valves.

 

[JHZR2]

Yes too high.

Did you pull a vacuum for a few hours or did you just add the refrigerant to the air in the system?

 

[229]

Did you replace the receiver/drier and oriface tube?

 

[robshelton]

Use a fan in front of the condenser and that pressure will decrease.

I use a large fan (or 3) to simulate the airflow of driving down the road when taking pressure readings. It's way more accurate. The general rule I'm aware of is the high side should be 2 to 2.5 times the aimbient temp (F.) for the best cooling. When mine is charged to the max I occasionally get a little frost blowing from the vents. Of course my thermometer will be reading in the middle 30-'s, so the temp at the evap is colder.

Use a thermometer in the center vent and post your results.The best temp check will be on the highway with the ac on low (not recirc) and measured in the center vents. If your pressures don't come down and your temp isn't in line you probably have a restriction in the high side. Think orifice tube or expansion valve type things. Good luck and post the results!

 

[RH+G]

Thays way too high. Is it even cooling at such a high pressure What is ur low side?

 

[harry j]

Too much oil?

 

[mechtech2]

That is high enough that the high pressure switch/blow off should trip.

But without proper airflow [a GOOD fan] pressures WILL go much higher than normal.
What's up with the concurrent low side pressures?

 

[2oldtommy]

A '90 Merc would have been charged with R12 originally. Yhe question is whether or not the conversion was done correctly. A professional job would include new decals indicating R134a refrigerant as well as the change in charging ports etc. If not, any number of things may be out of order.FWIW-Oldtommy

 

[Texan4Life]

being a r12 conversion I would expect to see high, high side pressures, but yes that is to high. I would keep it under 375 psi personally.

things that can cause this.. dirty condenser and or not enough airflow, a restriction (like a dirty orifice tube), or it is overcharged.

since you put on a new compressor, I can almost guarantee your orifice tube (assuming it has one) is dirty if not down right plugged up. It has a fine screen that catches wear particles from the compressor.

If it was overcharged that much the chances of it "cooling just fine" are pretty slim. since it would also start to run the low side up.

my .02