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is there such a thing as too big of a condensor?

vdubnut on Wed March 25, 2009 10:34 AM User is offline

Year: 1991
Make: chevrolet
Model: suburban
Engine Size: 5.7
Refrigerant Type: r134
Ambient Temp: 85
Pressure Low: 50
Pressure High: 325
Country of Origin: United States


last summer/fall i went through the process of converting over to R134..

i replaced the compressor, flushed the lines, replaced the o-tube, replaced the dryer, and vacuumed down the system.

when i went to charge things were going well, but then before i got to the proper amount of refrigerant in the system, the pressures began to get really high.

i just decided to leave it till this summer since it was fall and i wouldnt be using the air over the winter...

anyway, i believe the stock condensor is insufficent to remove enough heat and so the compressor just keeps running and the pressures get really shall i get the biggest condensor i can fit or is there such a thing as too much cooling from the condensor??

seems like the more the better?

mk378 on Wed March 25, 2009 11:02 AM User is offline

There is no such thing as too much condenser.

But consider the fan clutch and possible airflow issues (missing fan shroud, clogged fins of the condenser or radiator) first. If the fan clutch is the original one that came with the truck, it's very likely worn out.

vdubnut on Wed March 25, 2009 12:11 PM User is offline

thanks for the suggestions...

i doubt the fan clutch is the original as its a 1991 but there any way to test? it doesnt have any play in it like when they totally go bad...

the shroud is in place and the condensor looks clean and the radiator is new....replaced leaky one 2 yrs air flow should be ok...?

is there a suggested size/shape for this year suburban for a parallel flow condensor?

TRB on Wed March 25, 2009 12:23 PM User is offlineView users profile

If it's the original condenser an upgrade to a 6MM may help the higher pressures. As stated it would be wise to check that the fan clutch is working correctly also.

636420PL - 6MM Condenser


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vdubnut on Wed March 25, 2009 12:40 PM User is offline

it is an original....

how can i check the fan clutch?

i have not had any overheating problems...

iceman2555 on Wed March 25, 2009 1:03 PM User is offlineView users profile

The engine cooling system would be the primary consideration. This vehicle has a large tube and fin type condenser and should work adequately with 134a.
Average life of a fan clutch is 3 yrs/50k miles. Hopefully it is not the OE unit. Also, keep in mind that a fan clutch should never completely if yours seems to be decreasing in rotational speed, then it may be time for a change.
It was stated that the orifice tube was replaced and the system was flushed. What type chemical was used....and was it completely removed from the system? Failure to remove this extra chemical may result in increase pressures.
There is a unique factor concerning this model condenser....esp when the lines have been removed from the condenser....the fittings are the same thread size....and the hose bends are almost the other words...this condenser can be plumed incorrectly. Insure that the discharge line (compressor to condenser) enters at the TOP of the condenser. Of course, this means the liquid line (condenser to evap} is on the bottom.
Determining the correct recharge is also most important....a system that lacks a full charge will result in an increase high side (discharge) temperature/pressure condition. This condition will also result in an increase in compressor case temperatures. Lack of complete lubricant flow is also a result of this undercharge condition. This is a major cause of compressor failures on retro'd vehicles.
First check the engine cooling that all components work properly.
Secondly insure that the system is completely that the evap is flooded on this system. Doors open, high blower, max cool, engine at idle...measure the inlet and outlet temps of the evap...when they are the same...the system is properly charged. A slight variation of temps is more than 3-5 degrees.
Keep in mind also that pressures used on a retro fitted vehicle....are simply guesstamations. Make sure the system is fully charged....first step in any diagnosis procedure.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

vdubnut on Wed March 25, 2009 1:54 PM User is offline

when i flushed the system i used a large can of a/c system flush from autozone...not sure of the brand. but i put it in the lines and blew compressed air through them repeatedly to get it back out. i also did the same with the condensor and evap... also with the front to back lines. disconnected the rear evap and blew the cleaner out the back....i did this until i didnt get any more cleaner out....was a big messy pain in the butt!

i put in the specified amount of oil, dispersed into the lines, evap, and condensor prior to putting vaccum on it....

i was suspicious of a low charge because i was unable to get as much refrigerant into the system as i though it would take...85% of an r12 charge or thereabouts? i dont remember how much i put in(not what i had intended by calculation) but it got to the point where it wouldnt take any more...because the pressures got too high...i even was putting the r134 cans in warm water....kind of a double edged sword.....high pressure because of under charge and under charge because of high pressure...?

fan doesnt seem to slow down....and blows a ton of air when i rev it up...also quite a bit at idle...

orientation of the lines on the condensor were as i found them....i'll have to double check but i dont think they could be fitted incorrectly as they were different sizes inlet/outlet i believe.

vdubnut on Wed March 25, 2009 3:29 PM User is offline

i just went out and checked to make sure...

the compressor to condensor line is the top one and condensor to evap is the bottom one. mine must be somewhat different that the one you the two lines have different fittings and also are about 3-4 inches apart vertically.

bohica2xo on Wed March 25, 2009 4:11 PM User is offline

Fan clutches are usually overlooked because they wear out slowly, and you become used to the reduced fan howl.

Look HERE for info on testing fan clutches.

You can duct tape the gauge set to the windshield, and go for a drive. If you see normal pressures when moving, you have an idle airflow issue.

Cleaning the air path through all of the heat exchangers is a good idea as well. Small bugs & crud get lodged deep in the fins of everything in the stack. Use a drop light in the fan housing after dark, and look throughy the front of the condensor. It may be plugged up more than you think.


"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.

iceman2555 on Wed March 25, 2009 9:19 PM User is offlineView users profile

The 'flush' used may be a major contributor to this problem. AZ sells a 'oil based' flush. It is actually a light weight ester (POE) lubricant. It is almost impossible to completely remove this chemical from the system. It is quite possible that the system now has an over charge of lubricant/lubricant type chemicals.
Although no one wants to do something over, a suggestion would be to obtain a more suitable flush chemical and completely clean the system once more. Insure that all the chemicals are removed from the system. A good solvent based flush should be used and then the system 'air purged' using a clean/filtered air source. Drain the compressor....add the correct type/quantity of lubricant....the accumulator can be removed/drained and replenished with the correct type of lubricant. This will procedure will still maintain a 'slight' over charge of lubricant but the system should be able to absorb this overcharge.
It is imperative that the system be completely recharged.....the hard part of this is that this must be done no matter what the pressures are. This is necessary to maintain sufficient lubricant flow thru the system. It is hard to see pressures exceed certain levels. If after the system is totally recharged,the system experiences an excessive high side pressure..... then the engine/condenser cooling system must to altered to enhance cooling efficiency. Removal of refrigerant can and will effect compressor longevity. Many feel an undercharge of 5-10% can be detrimental to compressor longevity. This undercharge condition becomes more reliant in a retro because the system is being undercharged from the very beginning. This is often done to accommodate possible high pressure problems. Still is it necessary for the system to be recharged to a specific refrigerant level. In this is to insure that the evap floods under a heavy heat load. A compressor is designed to operate within certain undercharge conditions, however, there is a point (undercharged) where lubricant ceases to flow and the compressor begins to self destructor. This produces light debris fields which tend to restrict refrigerant flow and thus lubricant flow. The system finally fails completely due to this condition.
Good luck with your repair.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

vdubnut on Thu March 26, 2009 12:09 PM User is offline

so much for the claim on the AZ product that any residual cleaner is compatible with the system charge huh?

one other question and then i'll stop beating this horse to death....

say the problem is just an under charge and getting the additional refrigerant into the system would fix this....if i were to mist the condensor with a spray bottle of water while charging the system thereby increasing the heat removal through condensor, i may be able to get the "full" charge and maybe then the pressures would go down?

mk378 on Thu March 26, 2009 12:56 PM User is offline

It sounds like you have too much oil (some of it waterlogged from being in a used compressor), residual flushing material, some air in the system from using only a venturi pump, and an unknown situation with the OT. It would be best to clear everything out and start over.

More refrigerant is not going to help the high side go down if the problem is lack of condenser airflow and/or too much oil and/or air in the system.

HECAT on Fri March 27, 2009 5:54 AM User is offline

Originally posted by: vdubnut
so much for the claim on the AZ product that any residual cleaner is compatible with the system charge huh?

That claim is true. It will not evaporate with all the air purging you wish to try, and the residual POE in a sense, would be compatible. What the label does not say is that flushing is done to remove debris and oil to give you a clean and dry starting point. How can you put the proper oil charge in there when you do not know how much is still in there? You may have been more successful removing this from the tube and fin condenser because of it single tube path. But flushing the front and rear evaps without removing the OT or the rear TXV has surely allowed a lot of this product to pool and stay in the lower chambers of the evaps.


HECAT: You support the Forum when you consider for your a/c parts.


vdubnut on Fri March 27, 2009 12:38 PM User is offline

well im not sure what to do at this point. i thought i had gone through all the steps correctly...didnt know about the different "cleaners" i did however, remove and replace with a new one, the rear TXV to clear the lines and i did remove and replace the O tube so there shouldnt be all that much of the cleaner....also i put the cleaner back in the original bottle to make sure i got as much out as i put in ... also i bought and used a robinair vacuum...not a venturi type... starts to get to the point that the $$ put in end up more than the vehicle is worth....

question.... is the 636420PL - Condenser recommended a "true parallel flow" condensor....the best i can get, if i decide to go that route?

thanks for all the suggestions...this is really a great site.

TRB on Fri March 27, 2009 1:19 PM User is offlineView users profile

It's a 6mm Piccolo Style PF condenser.


When considering your next auto A/C purchase, please consider the site that supports you:

iceman2555 on Fri March 27, 2009 1:26 PM User is offlineView users profile

I performed a bit of research for AZ flushes...for more reasons than one.
They do offer a 'ester' based flush but also...unfortunately...they also offer a solvent based flush. Checked the MSDS and lo and old friend/enemy was present.
'CONTAINS: 65-75% ODORLESS MINERAL SPIRITS (64742-48-9)[265-200-4],20-30% D-LIMONENE (5989-27-5)'
Mineral spirits is, of course, and excellent cleaner/degreaser.....but it is impossible to remove from a system without the use of an additional flush to remove the mineral spirits.
Have seen numerous returned units that failed due to this chemical.

These are examples of systems flushed with a similar mineral spirits based chemical.
If either of these flushes, ester or mineral spirits, were used....simply changing the condenser will not save your system. If there is any your system prior to the installation of a new condenser. If the condenser is replaced and these chemicals result in a failed may be that your new condenser will be lost also......there are no short cuts to a successful AC repair.
Good luck

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

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