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lesrwoody on Fri June 11, 2010 6:04 PM User is offline

Year: 2004
Make: chevy
Model: avalanche
Engine Size: 5.3
Refrigerant Type: r134
Ambient Temp: 95
Pressure Low: 30
Pressure High: 250
Country of Origin: United States

does any one know what would cause low side pressure to drop low enough to make low pres switch disengage the clutch no matter how much freon is in your system.
04 avalanche 1500 25.50 ounces
at idol 60psi low side and 250 high side orphise filter replaced system vacuumed 28 inches of mercury
thanks

HVargas on Fri June 11, 2010 6:37 PM User is offlineView users profile

Does the compressor engage if you jump the terminals in the switch harness. If you are getting 60psi on the low side, that is more than enough to engage the compressor.

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Edited: Fri June 11, 2010 at 6:39 PM by HVargas

GM Tech on Sat June 12, 2010 6:47 AM User is offline

With your quoted pressures of 30/250 at 95 degf amb- that is about perfect! What is the issue-- does truck cool? why do you want it to cycle so bad? The truck cools the best when compressor is running....cycling normally occurs when there is extra capacity, and system cuts off compressor to avert evap freeze. Low blower speeds will iduce lower suction pressure which will encourage cycling- but at 95 degf amb, I doubt much cycllng will occur- try it at 65 degf amb - then it will cycle- if that is what you want it to do so bad.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

lesrwoody on Sat June 12, 2010 8:00 PM User is offline

no the truck will not cool,the compressor clutch kicks out at 30 degrees.the only way i can get the truck too cool is set low side pressure at 60,then the air out of the vents will hit 60.but i cant seam to get the truck too cool below that.the problem im having is when i charge the sys with gauges to correct pressure 4042 psi low side at 1500 rpms it keeps acting low?compressor will kick out then blow stale air then it will engaudge and the cool air is back and so on . at my first posted pressures thats all it will do.it never gets cool cuz the compressor will not stay engaudged i dont want it to cycle i cant stop it thats the problem .im new at this so if i say something stupid sorry. thanks for your reply

Edited: Sat June 12, 2010 at 8:05 PM by lesrwoody

GM Tech on Sat June 12, 2010 8:41 PM User is offline

You should be charging by weight or volume, not by supposed pressures. Put in the amount specified on your underhood sticker and report back your results...

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

lesrwoody on Sat June 12, 2010 9:09 PM User is offline

sticker is gone,but i was told its 25.50 onces .not sure where to get this info.dealer maybe?also i should say my compressor seams to be whining some,and their were a few metal flakes in the filter.when i say a few i mean 4 or 5,also some sort of rubber pices not like oring pices but strait and small?

GM Tech on Sun June 13, 2010 8:55 AM User is offline

25.50 ounces for front system only-

if you have rear air its 43 ounces total

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

lesrwoody on Sun June 13, 2010 10:03 AM User is offline

i don't have rear air i don't guess only thing in back of truck is 2 vents is that rear air? no contrllos just vents,but you maybe on to something here cuz my dryer isnt sweating and when i charged it to where it would cool at 60 degrees it started to have a little seweat on it,and the low pressure hose to the compressor started to sweat some too.both lines out of evap are not cold.just one of them.i was thinking the dryer should be sweating a good bit also?

Edited: Sun June 13, 2010 at 10:56 AM by lesrwoody

GM Tech on Sun June 13, 2010 11:39 AM User is offline

If you have rear air you will have option code C69 on your options chart

you will have a line split just beyond the condenser, and a return line join in at the accumulator- between it and the compressor

you will have rear air controls, fan speed etc

you will have a rear evaporator

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

lesrwoody on Sun June 13, 2010 1:33 PM User is offline

oh well i didn't think that was the case but thanks for the info. ok i got it to 50 degrees now while drive ing down the road but when i stop the air starts to get back around 60.im sure it is a little overcharged but if i try to charge it at 40 degrees it wont cool.also i noticed that if i turn my fan to low it seams to get cooler? i also checked the blend door actuators but they seam to be working.im bout ready to give up!but i don't like just anyone fooling with my truck , it belongs too me and i know i will do the best i can to get it wright,when others will just try to rig something up.thank you for your replies your info is very helpful

mk378 on Sun June 13, 2010 1:57 PM User is offline

You really have to take all the refrigerant out down to vacuum, then charge by weight, and if it still doesn't work well then you'd know something else is wrong. Otherwise you're just guessing.

If you can't run the specified charge without excessive pressure, it could be bad condenser cooling, overcharged with oil, or blocked / incorrect orifice tube. Cooling a lot better on the road than at idle suggests a condenser airflow issue.

lesrwoody on Sun June 13, 2010 3:52 PM User is offline

i did take all the 134 out and vac the sys leak test held, then i got the amount from a local parts guy of 25.50 onces.this guy is a real parts guy not autozone guy,so im sure he gave me the wright amount to put in i used the 12oz cans and put in 2 full cans and a little of the 3rd can,that should have been enought wright?.not an air vac pump but electric im not a pro at this but i have charged sevral sys befor and never had any problems like this. i have tried puting more in but that just drives the head pressure up to 300 on hot days and i was always told it should never get above 250 is that so?i will read the static pressure and post it may be that will tell you all something. thanks guys. oh and i have replaced fan clutch.

Edited: Sun June 13, 2010 at 3:54 PM by lesrwoody

lesrwoody on Sun June 13, 2010 4:35 PM User is offline

static pressure 120/120 its hot in georgia 95 degrees!

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