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High-Side Pressure too High

91bimmer on Thu July 01, 2010 7:22 AM User is offline

Year: 1991
Make: BMW
Model: 325i
Refrigerant Type: R12
Ambient Temp: 68
Pressure Low: 23
Pressure High: 300

My a/c has never worked too well although it's never leaked all the refrigerant out. I recovered the R12 and replaced a leaky pressure sensor that would only leak when the a/c was running. I also replaced the TXV and receiver/dryer. I then refilled with new R12 after pulling a vacuum. I used a 30lb can of R12 and burped the lines before injecting the refrigerant so I'm certain no air got into the system

I'm not sure if I have a problem but here are the pressures...

700rpm 68°F Ambient: Low side - 33psi ... High side - 180psi

2000rpm 68°F Ambient: Low side - 23psi ... High side - 300psi

I had to run then engine for about 3 minutes at 2000rpms to get the high side up to 300psi. So it doesn't just jump from 180 to 300psi as soon as I rev up the engine.

Does it sound like I have a blockage somewhere? The high side pressure is read Between the receiver/dryer and the evaporator TXV. So the high pressure is read AFTER the condenser and receiver/dryer and before the evaporator. There is a #6 metal line between the high side port and the evaporator so I'm thinking that might have corroded or filled with gunk (stop leak??)??? Could the blockage be before the high side port like in the condenser?

The ambient was cold (68°F) so I really couldn't tell how well the a/c was working because of course it's going to blow cold at those outside temps. It will reach 90°F on Sunday so I will definitely find out then how well the a/c works but I suspect that if the high side was 300psi with 68°F ambient then it's going to be much higher once the ambient temps increase. The high pressure switch will turn off the compressor at 380psi.

Any suggestions of what/where the problem lies?

91bimmer on Thu July 01, 2010 7:32 AM User is offline

Want to add one more thing.

According to the sticker under the hood, the system holds 2.15lbs ± .05lbs. I accidently added 2.25lbs although much of that extra 0.05 lbs was lost in the lines going to the system.

mk378 on Thu July 01, 2010 11:29 AM User is offline

Are the condenser fans OK? Condenser and radiator clean on the outside? Pressure like that usually means the condenser is not getting adequately cooled.

91bimmer on Thu July 01, 2010 11:49 AM User is offline

The 2-speed condenser fan is working. It operates at low speed when the a/c is on which is how it's supposed to operate from the factory. I did manually turn the fan on high speed to see if it had any affect but it didn't.

Also the radiator and fan clutch are brand new. My old radiator was full of gunk and you couldn't even see through the fins. I'm really stumped as to why I'm getting such high pressure and even poor performance at idle.

mk378 on Thu July 01, 2010 1:51 PM User is offline

Gunk in the condenser fins too then? Fan shrouds or air blockers missing?

The system should definitely be trying to kick the electric fan up to high when the pressure is 300.

91bimmer on Fri July 02, 2010 10:06 AM User is offline

Alright I did some research. The electric fan operates independent of the a/c. The a/c turns on the low speed but that's it. The fan primarily operaties via a radiator temperature sensor. If the sensor reads very hot, then the fan will operate in high speed.

I did install a new condenser when I did the radiator. I also used the radiator shroud. I believe everything on the car is stock with no modifications. So it should be working as intended from the factory. I guess maybe the condenser is no good if it can't cool the r12 at idle???

bohica2xo on Fri July 02, 2010 3:23 PM User is offline

In your first post, you did not mention replacing the condensor - but you did mention stop leak.

WAS stop leak ever used in this vehicle? If so you could have a blockage ANYPLACE in the system.

Your replacement condensor - was it purchased from a popular online auction site for less than 40 bucks - with a "lifetime warranty"? Tube & fin construction?

The proper condensor for that car is a high performance serpentine, worth about 200 bucks.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

mattd860 on Fri July 02, 2010 4:05 PM User is offline

sorry about the lack of info. I bought an oem Behr condenser for $150 bucks and it was brand new. The stock condenser is tube and fin and so is the new oem condenser that I bought. Was thinking about using the parallel flow condensers sold here on ackits.com but decided to stay stock. I have never used stop leak but just mentioned it just in case the previous owner used it (which he probably didn't). I was also just trying to justify a blockage because I have no idea how a blockage can occur without using stop leak or serious corrosion.

bohica2xo on Fri July 02, 2010 4:26 PM User is offline

A blockage will show up as a cold spot in the line at higher rpms, along with poor cooling at the evaporator.

Misting some water on the condensor should drop the high side if it is just a poor condensor.

Both of the replacment condensors for that vehicle are serpentine units Look HERE for the parts listings. If you indeed have a bad condensor, replace it with the serpentine unit.

You could have a counterfeit Behr part. The chinese copy stuff all the way to the mfg. logo...

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

91bimmer on Fri July 02, 2010 4:50 PM User is offline

Quote
Originally posted by: bohica2xo
A blockage will show up as a cold spot in the line at higher rpms, along with poor cooling at the evaporator.



Misting some water on the condensor should drop the high side if it is just a poor condensor.



Both of the replacment condensors for that vehicle are serpentine units Look HERE for the parts listings. If you indeed have a bad condensor, replace it with the serpentine unit.



You could have a counterfeit Behr part. The chinese copy stuff all the way to the mfg. logo...



B.

Well the old condenser that I took off which I assume is stock, was tube and fine. This is all very interesting though!! I'll try misting the condenser and see if pressure drops. If it does then i'll buy the serpentine one. Will get even better performance if I went with the parallel flow condenser instead of the serpentine??? Thanks for the info!!!

mattd860 on Sat July 03, 2010 1:24 PM User is offline

Let me know how it works with the serpentine condenser.

Edited: Sat July 03, 2010 at 1:54 PM by mattd860

91bimmer on Sat July 03, 2010 1:53 PM User is offline

Ok I misted the condenser with water and the pressure dropped dramatically. Below are the stats while misting condenser:

ambient 80°F - engine 700rpm - high side 150psi - Low Side 33psi

ambient 80°F - engine 2000rpm - high side 130psi - low side 22psi

Both tests yielded 40-45°F air temps from the vents.

I'm going to buy the serpentine condenser next week. I have a question though - the serpentine condenser core is about 14" x 14" however the stock tube & fin condenser core is about 14"x17". Since the serpentine condenser is smaller, will I still see an overall improvement?

bohica2xo on Sat July 03, 2010 3:22 PM User is offline

Obviously a condensor issue, and not a line restriction someplace.

Since you are sure the airflow is good, all fans working, seals & shrouds in place etc. - I will say that condensor is the issue. That is a dramatic change.

Serpentine & PF condensors are shockingly good when compared to older tube & fin units. Many times a replacement is the same size as the T&F unit - but half the thickness.

There are two condensors listed for that car, you must have the unit with the #6 & #8 hose connections. It is a bit smaller but more effective at transferring heat. It should be fine, just make sure it is getting good airflow.

You could of course fit the larger unit if you felt like modifying the vehicle. I don't know how extensive a job that would be on this particular vehicle.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

91bimmer on Sat July 03, 2010 3:49 PM User is offline

i did some sizing up and the larger serpentine definitely wont fit. the 14x19.5" parellel flow condenser should fit fine though but i will have to fab up some new hoses going to/from it. should i go with PF or serpentine?

bohica2xo on Sat July 03, 2010 6:11 PM User is offline

Given the choice, I would use a larger than OEM PF unit. If you are comfortable installing a condensor like that & changing a hose or two - Great!

It is impossible to put too much condensor in a passenger car. As you saw by spraying water on your old T&F unit, the high side pressures drop. So the compressor works less, parts last longer...

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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