98 Suburban a/c pressure -30 low-155 high

[cris2004]

I've put in a new Delco compressor, oriface tube, rear expansion valve and dryer. I pulled out the condensor, it did not seem to have any restriction. Same for all the lines, low muffler is cool, high muffler hot.

At idle I get 42/150, at 1800rpm 30-32/155, this at 80 degrees.

The truck cooled great (30/290) before sitting a couple months, then I had similar problems. I thought the compressor or clutch was weak, so I replaced it. The original cooling wasn't as good with the rear air on, so I changed the valve there as well.
I had a few black specs on the O-Tube.

There is so slight a difference in the high pressure at low and high RPM's, I wondering if there is a pressure controlling device outside of the high and low cut -off switches. There is the pressure valve in the back of the compressor, one that gets moved into the new one, but I understand it's another emergency relief.

None of my books have this low side -normal / High side low scenario. Anyone have an idea?
Thanks very much!
Chris

[brcidd]

A common a/c failure mode on C/K trucks- is mechanic's mistakes:

1. the condenser is plumbed backwards..

2. There are 2 orifice tubes in system.

Your threads on both ends of condenser are the same...did you assure the compressor feeds the TOP of condenser?

There is to be NO orifice tube in outlet of condenser for a dual air system, are you sure no one put an OT in the outlet of condenser? Yours should be after the "Y" split, downstream from condenser.

[j cAT]

Originally Posted by cris2004

I've put in a new Delco compressor, oriface tube, rear expansion valve and dryer. I pulled out the condensor, it did not seem to have any restriction. Same for all the lines, low muffler is cool, high muffler hot.

At idle I get 42/150, at 1800rpm 30-32/155, this at 80 degrees.

The truck cooled great (30/290) before sitting a couple months, then I had similar problems. I thought the compressor or clutch was weak, so I replaced it. The original cooling wasn't as good with the rear air on, so I changed the valve there as well.
I had a few black specs on the O-Tube.

There is so slight a difference in the high pressure at low and high RPM's, I wondering if there is a pressure controlling device outside of the high and low cut -off switches. There is the pressure valve in the back of the compressor, one that gets moved into the new one, but I understand it's another emergency relief.

None of my books have this low side -normal / High side low scenario. Anyone have an idea?
Thanks very much!
Chris

the exact pressures will not be found very easy...I remember years ago seeing this detailed info ...

basicly with the ac fan on max, engine RPM 1500-2000 the low side should be 40psi area with the air temp @80deg F , the high side is variable on vehicle type ETC..

when adding refrigerent , monitor the high side pressure when you see this pressure go above the 175 psi area this should indicate that the system has suffecient refrigerent to operate correctly...

If you continue to add refrigerent and suddenly see a rapid increase in the high side pressure then you have added too much...

I always slightly under charge the system...I always add 4 OZ of oil to a system that has never had any oil added since manufactured. this reduces seal leaks...use PAG 150..check to be sure ..

better to be too low on refrigerent..too much and you will destroy the compressor valves..too much oil is no big deal it only reduces the effeciency slightly..

the prior compressor readings the high side was 290 psi...If the air temp was 110 deg f ok..if 80deg f that would be too much pressure...could be bad engine fans/fan clutch/dirty exterior of condensor..too much refrigerent.

[cris2004]

I'm sure I got the condensor in right, the lines left attached wouldn't allow it any other way.
I don't know where a second O tube is! The one I replaced is indeed after the split. The rear has an expansion valve. Where would the second one be?

I agree too much oil can hurt slightly, in my case it wouldnt allow the low side to get down due to the density. I'm sure I have the right charge, I used a digital scale after pulling down to -28. I cant' get that high side to budge up! It used to be over 250 on a warm day and 300 when hot (100 degrees)

[j cAT]

Originally Posted by cris2004

I'm sure I got the condensor in right, the lines left attached wouldn't allow it any other way.
I don't know where a second O tube is! The one I replaced is indeed after the split. The rear has an expansion valve. Where would the second one be?

I agree too much oil can hurt slightly, in my case it wouldnt allow the low side to get down due to the density. I'm sure I have the right charge, I used a digital scale after pulling down to -28. I cant' get that high side to budge up! It used to be over 250 on a warm day and 300 when hot (100 degrees)

oil will not effect the pressures any ....air in the system will cause higher pressures with the correct charge..

I would say the compressor is N/G....not pumping good..

low pressures hi/lo side with the correct charge !

my vehicle 90 deg f its around 225psi hi side ..

[cris2004]

I'm fairly sure it's not the compressor. I tried an off brand before going back to a new Delco, having the same problem still not fixed. With the high pressure side at 150 I'm getting 70 vent temp on an 85 degree day. Yuch.
I tried adding freon though I know I'm filled, it would raise the low side but not improve the high side.
It worked great before sitting couple months. I've made several attemps now and am running out of ideas lol. I'm going to acess the evaporate even if I cant see what it could do to in a case of 25 low / 150 high. Could be an evil squirrel I guess.
I was hoping there was some sort of high pressure control device keeping it low. It seems odd that from idle to high speed reving it barely budges the high side needle.


Thanks

[j cAT]

[quote=cris2004;6894779]I'm fairly sure it's not the compressor. I tried an off brand before going back to a new Delco, having the same problem still not fixed. With the high pressure side at 150 I'm getting 70 vent temp on an 85 degree day. Yuch.
I tried adding freon though I know I'm filled, it would raise the low side but not improve the high side.
It worked great before sitting couple months. I've made several attemps now and am running out of ideas lol. I'm going to acess the evaporate even if I cant see what it could do to in a case of 25 low / 150 high. Could be an evil squirrel I guess.
I was hoping there was some sort of high pressure control device keeping it low. It seems odd that from idle to high speed reving it barely budges the high side needle.




what did you use to check the vacuum when you pumped down the system ? just the guage set ? how long did you wait to see if the vacuum held 1 hour or so ? the larger the system the longer the pump down required..when you installed the new compressor did you dump out the oil and install new compressor oil ? how much oil did you add to this system ? what is the spec on the oil amount ? it is more with your vehicle ..

the pressure controlling is the pressure switches..this will cut power to the clutch..

defective compressor/clutch slip/belt slip/..

[cris2004]

I did use just a gauge set to watch the vacuum. Is there a better way? I left it on for several hours, then shut it off, and shut of the valve at the pump. The vacuum held overnight, I restarted it for an hour and filled the freon.
I think the compressor was shipped with out oil, or at least oil I should dump out. It said to add 2 or 4oz, I followed whatever it did say. The accumulator was pretty much dry, I added two to that as well. The book says 11 oz in the system. I'm not getting any particular noise from the new compressor, but I am honestly not sure of the oil total as I have not flushed the system.
I have a newer drive belt.
I hear ya on the defective comp, slippage, that was my original thought. I must be overlooking something moronical.
Thanks again for the help.

[brcidd]

Originally Posted by cris2004

I'm sure I got the condensor in right, the lines left attached wouldn't allow it any other way.

Please double check-your plumbing- your lines do have same connectors on them-and are possible to install backwards- I just looked at the replacement condenser. Your pressures indicate a condenser issue, and this is the only thing that comes to mind to resolve your issue.

[cris2004]

Fair enough. The top is coming in from the compressor outlet.
I really should have replaced it altogether. I didn't since I would have thought I'd have high pressures if it was restricting. I'm suspicious of the muffler/filters too but I may be just grasping at stuff.
Thanks

[brcidd]

No one tried to put an OT in outlet of condenser while it was out did they?

[cris2004]

No oriface tube in the condensor. I really wish I changed it, but wouldn't a plugged, restricted condensor cause high head pressures?

[cris2004]

What is the proper way to check an evaporator or condenser for partial blockage after removing them?
Thanks!

[mishalah]

I just did mine a few days ago and the readings are similar...approx. 30-34 and 175. I didn't take a reading on the vent temp with the windows open and running high, but I know it gets colder when being driven instead of sitting on the driveway.

I replaced compressor, drier, and OT. I have to think that the newer compressors might not require the higher high side pressures as the old ones. I'm gonna retest everything an another week or so as it gets hotter outside.

[MT-2500]

Originally Posted by cris2004

I've put in a new Delco compressor, oriface tube, rear expansion valve and dryer. I pulled out the condensor, it did not seem to have any restriction. Same for all the lines, low muffler is cool, high muffler hot.

At idle I get 42/150, at 1800rpm 30-32/155, this at 80 degrees.

The truck cooled great (30/290) before sitting a couple months, then I had similar problems. I thought the compressor or clutch was weak, so I replaced it. The original cooling wasn't as good with the rear air on, so I changed the valve there as well.
I had a few black specs on the O-Tube.

There is so slight a difference in the high pressure at low and high RPM's, I wondering if there is a pressure controlling device outside of the high and low cut -off switches. There is the pressure valve in the back of the compressor, one that gets moved into the new one, but I understand it's another emergency relief.

None of my books have this low side -normal / High side low scenario. Anyone have an idea?
Thanks very much!
Chris

To your first post.
Cooled good before sitting a couple of months I woulkd suspect a leak someplace.
Has the pressure changed from first repaired and cooleing good and after setting a coulpe mo's?
I would suggest you pump it out and recharge with the proper charge and see if it cools/works good.
If so run a leak test on system.

As to your last post on proper pressure.
Depends a lot on air flow threw condenser and out side tempt and engine RPM.
When ckecking pressure get engine warm and I always put a window fan in front condenser and make sure radiator fan is kicking in good.
At idle low pressure can range 35-40 and high should be over 150 up to 300 or more depending on condenser cooling and AC charge.
At 2K RPM low side may drop to 26 to 34 and high side range 175 up.

Vent temt cooling will be a little over low side pressure.
Rule of thumb evaporator cooling temp will match low side pressure.
28 low side pressure will give 28 degrees cooling.

As to checking for restricted condenser or evaporator you should watch pressure reading and take a tempt reading all over condenser before taking off.
A temt reading on condenser or evaporator will show a clogged up or not working spot.
Berfore and after a set/correct AC charge.
Post back all of your low and high pressure readings idle and at @2K and vent tempt and outside tempt readings.