A/C system - Not functioning, need help!

Question

1996 Chevrolet Tahoe 5.7

When i bought the vehicle, the a/c system was never working. Replaced compressor (seized clutch), replaced accumulator, replaced o*****e tube and leaked checked (none found). System was filled with proper amount of refrigerant. Recharged, but there is no flow.

When Air Conditioning is turned on, compressor clutch kicks in. But the 'High Side' needle shoots right up, onwards to 400 lbs. As for the 'Low Side', manifold shows around 80 lbs. 'Low side' lines/hoses are not cold, and high side lines/hoses are hot.

There is probably a clog somewhere. I tried blowing compressed air through the lines(not advisable), removed high and low side valves, and blew in through the high side. And air came out of the low side.

Everything appears to be functioning the way it should be but, what else could it be?

**I've already recharged the system 4-5 times, trying out different solutions but, no go. And also tried flipping the o*****e around, but same thing. Blew air through the condenser and that's also good.

Answer 1

I too am ase cetified,- 30 years ago when that first came out, an did service on referigreants 20 years before that!  I was there when this cruddy system first came out! They saved about $40 a unit by not putting a standard thermal expansion valve in system, -- instead using the "critical charge system". This works ok as long as everyting works almost perfect! 1/2# too much or too little freon knocks it dead! So the first question I would ask, is just how much freon are you putting in?

Next thing is to feel lines in and out of condenser Line should bve real hot on high pressure side going in, should also be hot coming out,- but not as hot! Since condenser is supposed to dissipate some of heat into air! (this is actually the heat absorbed by cold in evaporator!

I hav e seen components installed with the plugs in lines somewhere, - so though it sounds dumb, are you absolutely sure that you removed plugs? Check condenser lines if you have not done so yet! Freon must flow through there too!

Now here is how to get the right charge! Even if you have no measuring equipment like the manual says!  After you have evacuated the system etc. Start freon flowing into low pressure side!  Have engine running faster than normal idle -- maybe 1500rpms,- all doors on vehicle open controls set to maximum, - note that the clutch clicks on and off rapidly! As you add freon, the "run time" on compr. should get longer between click off!  It may not have enough pressure to turn on safety shutoff switch, so you may have to remove plug and put jumper wire in it to keep compresor running normally! Anyway, continuing on, - when you have enough freon in to cause compresser run to last about 45 seconds, stop adding, and wait 4-5 cycles for pressures to equlize in system!  By now the top of accumulator should be getting fairly cold, - if not you have problems yet! I am guessing that you should have earound 2 1/2# in by now, Also by now the safety switch should work so plug socket back on!  now properly filled properly working system will flash frost just before compressor shut off each time! I always put palm of left hand on top of accumulator,- when cold ecomes unbearable you are real close to max performance! Now when the frost "flashed in moisture there", the system can not get any colder, continuing to add will go back to short cycling, and very high pressures everywhere -- especially if you "jumped thermostat" so clutch will not cycle at all!

You did not get something with shutoff valves operated externally did you? If you have them make sure they are turned open! Haven't seen any in years, but some re-manufactured stuff from Mexico could posibly have them on connectors from compressor!   In the "old days" we used to shut these off when removing connections, and it would hold part of freon from system inside compressor, -- which you could then use to "blow" air out of system when finished -- thus bypassing need for vacuum pump when far from shop!  By the way R-12 was 50 cents a pound in bulk -- wholesale!  But or government came along and fixed that -- (even though EPA later said it makes no difference in ozone!)

Answer 2

If you've got 400 and 80 at the same time, then it sounds grossly overcharged.  Do you keep doing the same charge over and over?  If so, why?  Aren't you curious about what it would do pulled down to 20 or 30?  It can't get cold unless the low side pressure gets down.

Answer 3

I am an ASE cerified master tech working at a dealership. I recently had a similar problem which was resolved by replacing the condenser in front of the radiator. This particular unit had a small receiver/dryer built into the condenser coils which was the clogging point. Try disconnecting the hoses feeding into and comming out of the condenser and see if shop air will blow through the condenser with sufficient force to allow good volume of flow. Watch out for the oil all over the place scenario! You stated that you have airflow from the high to the low side when blowing through the service ports. This should be done by disconnecting the actual lines and blowing through in series, instead of blowing into the service port where there is a parallel path for the pressurized air. Another problem might be too much oil or too much freon.

Answer 4

you need to take the lines off the compressor and off the evaporator and get a can of ac flush and flush the entire system including the condensor and evaporator, also afterwards make sure you have the proper amount of oil in the system. another question did you use an ac system to vacuum the system down after you changed the parts