air conditioning

[p38js]

how much R134A freon does my 95 suburban hold?

I serviced the freon today set the high side to 150psi and the low side to 30psi. I noticed that when I had the a/c on the compressor would cycle on and off, when I would turn on the a/c for the back passenger the compressor would not cycle on and off. is ths normal operation. the pressure did not change when the back was turned on and off.

 

[Acesneights1]

You cannot charge a GM system by pressure. It is a measured charge and best not to deviate from it. Should be a sticker on the a/c box or rad support saying how much. If not maybe someone on here with a burb with rear a/c can help you. Do not over charge it.

 

[THEFERMANATOR]

roughly 2.3 lbs for a 95 with dual air is what the sticker on mine said before. The charge should be closer to 3 pounds though IIRC. The 95 only holding 2.3 makes no sense since the 96 holds 4.1 pounds and the only fifference is the hose assembly at the compressor and the compressor itself.

 

[Kick Ass Matt]

my 94 holds 4 pounds
If your comp is cycling on and off then your charge is low.

Depending on your ambiant temperature your low side should be around 35 and up. On a 95 deg day it would be humming around 45 - 50 low side

Matt

 

[jmiller]

There's a chart in service manuals that shows the High Side / Low side pressure relationships. These are pretty much independent of system size and temp.

Any particular low side or high side pressure is dependant on the outside temperature.

I was topping off a charge on my truck by pressure, it was 20 / 175. Added until it was in the 30/250 range.

It is best to charge by weight. But partial charges can make this impossible with out recovering the entire system.

Over charging the system floods the system. This is extra high and low side pressure, and causes ineffective cooling.

Low charge is symptomatic of compressor cycling.


A reasonable way to tell, is watch for the compressor to stop cycling. Check the accumulator for a level of temperature differential. This signals excess refrigerant in the system. Some is ok, I've used an inch or so as an indicator.

Recharge methods:
Best is by refrigerant Weight
Second is Sight glass in liquid line, No bubbles
Third is pressure differential chart
Forth is compressor cycling / accumulator temperature diff.


Some systems don't specify weights, like R12 conversions, off road and farm equipment, etc.

Some people, I know, will only use a sight glass. They will add one if the system doesn't have one. (don't recommend)

When using pressures, make sure the condenser is clean and has good air flow!!! A blocked condenser will jack the pressures around and cause you not charge properly. Blocked orifice tubes can also cause issue with pressures.

If you know the system is clean, inside and outside, charging by pressure is a good option.

John

 

[THEFERMANATOR]

I just checked my ALLDATA and it calls for 2.2 for single and 4 for dual, I wish I still had the factory label from mine as it said 2.3 for dual which I always thought wasn't enough.

 

[Brooklyn Tow]

3500HD reg Cab.......from sticker = 2lbs of 134.

If that helps.

 

[turbovanman]

There's a chart in service manuals that shows the High Side / Low side pressure relationships. These are pretty much independent of system size and temp.

Any particular low side or high side pressure is dependant on the outside temperature.

I was topping off a charge on my truck by pressure, it was 20 / 175. Added until it was in the 30/250 range.

It is best to charge by weight. But partial charges can make this impossible with out recovering the entire system.

Over charging the system floods the system. This is extra high and low side pressure, and causes ineffective cooling.

Low charge is symptomatic of compressor cycling.


A reasonable way to tell, is watch for the compressor to stop cycling. Check the accumulator for a level of temperature differential. This signals excess refrigerant in the system. Some is ok, I've used an inch or so as an indicator.

Recharge methods:
Best is by refrigerant Weight
Second is Sight glass in liquid line, No bubbles
Third is pressure differential chart
Forth is compressor cycling / accumulator temperature diff.


Some systems don't specify weights, like R12 conversions, off road and farm equipment, etc.

Some people, I know, will only use a sight glass. They will add one if the system doesn't have one. (don't recommend)

When using pressures, make sure the condenser is clean and has good air flow!!! A blocked condenser will jack the pressures around and cause you not charge properly. Blocked orifice tubes can also cause issue with pressures.

If you know the system is clean, inside and outside, charging by pressure is a good option.

John

Good advice and I'll add one more, MAKE sure the clutch fan is working. I just did a Ford repair and at idle, it didn't do a thing except freewheel, sent my high side pressures thru the roof. New clutch fan, fixed.

 

[p38js]

thanks for the info guys. Still do not understand when the ac is turned on with the rear turned off the comperssor cycles when I turn the rear on the compressor does not cycle. I guess I will have to put the machine on it and suck it down and service it up with 4lbs of freon.

 

[THEFERMANATOR]

thanks for the info guys. Still do not understand when the ac is turned on with the rear turned off the comperssor cycles when I turn the rear on the compressor does not cycle. I guess I will have to put the machine on it and suck it down and service it up with 4lbs of freon.

That ones easy. Pressure is a direct function of temperature, and these systems turn the compressor off and on via the low pressure cycling switch. When the rear air is on you are pulling more BTU's out of the A/C system which raises the pressure in the system as you put more heat into it essentially. With just the front air on you are using less BTU's of cooling so the pressure drops in the system some and the compressor cycles.

 

[Missy Good Wench]

Here is the playbook from Missy's Garage.

I start with an empty system and add 134 until the compressor cycles correctly.

Now correctly is dependant on ambient temperture outside.

Watch the high side pressure. 150 is not bad. The low side will control the on off of the clutch.

These are clutch cycling systems. The rear AC will have an effect on the whole system as it changes the amount of latent heat coming into the refrigerant.

Check the outlet air temp at the vents.

On an 80F day you should be able to get 40F discharge air when running down the road.

(OR CLOSE)

If the clutch cycles very fast, your low on refrigerant. This will also see a highside pressure that is too low also.

Its nice to be able to install just the right amount of 134 but unless you have a scale?tools to do this accurately I just use the high and low pressure along with the discharge air temp.

Done this for years, never an issue. Its not too hard to hit the "sweet spot"

Just dont get too much as the system wont like it and you can stall the compressor9NOT GOOD)

The front system uses an orifice tube to meter the 134 into the evaporator, the rear is controled by an expansion valve in the inlet side of the evaporator.

The expansion valve allows refrigerant to flow into the evaporator until either the core temp or the outlet pipe temp is where it needs to be. At this point the valve closes off the flow until the temperature rises enough to open the valve again.

The expnasion valve is a nice way to go as they can more closely control the refrigerant flow as compared to a orifice tube.

The OLD GM systems (70's) had what was called a suction throttling valve in the low side line.

This device controlled the return line "Vacuum" to the compressor. These were used in conjunction with an expansion valve to give very reliable service.

These old systems did not cycle the clutch and even on a hot day would freeze the nuts off a brass Monkey.


Another little tid bit.

There is a Product called Envirosafe. This refrigerant comes in a mustard yellow canister and has a PINE odor to it.

Its ability to cool is far better than 134 and 12. This material is compatible with all the oils used in these systems and wont screw up the seals as did the 134 when doing a retrofit on a 12 system.

The envirosafe is a Hydrocarbon based refrigerant (HC) and from what I have read, it will burn if you get it hot enough.

The temps required would incinerate your truck so its no worries there.

It takes only about 1/3 the amount of the material to do the job too.

I have used it to refil some old 12 systems. Stuff works great.

An R12 system refited to use R134 just does not get it done, the condenser is too small to work well with the R134 and this results in less than stellar performance.

Keep in mind though that by law and by fitting design, you must "Convert the R12 system" to use R134 first. (Fitting conversion kit)

Its common for the rear units to have issues with the expansion valve and not work, and the front unit work fine.

If your getting good cold air from the vents (40F to 45F depending on ambient) your good to go.

Another thing to remember is that if you are replacing any components you need to be sure of the oil fill in the system.

Refrigerant oil in the system mixes with the refrigerant and flows along in the stream. This lubricates the compressor.

Replacing an evaporator, condenser and or accumulator (Silver can on the firewall)
you will need to check the specs and add the proper amount of replacement oil.

There is PAG oil and Mineral oil and one other, can't bring it to mind right off but the 134 will not work wityh mineral oil. R12 likes mineral oil.

The Envirosafe will get intimate with any of the stuff.

There are several replacement Refrigerants on the Market but most require an HVAC license to buy them at the supply houses.

R134 and the Envirosafe products dont require these credentials.

Always be safe with this stuff as it is very cold and can cause severe burns to the eyes and skin upon contact.
Also there are very high pressures in play here too. DONT ever connect the cans or pail to the high side port. Also never open the high side valve on a gauge set when the rig is running.

Doing so can over pressure the container and result in a nasty explosion.

The low side is where to feed refrigerant into.

I like to pull a vacuum of 29" on the system using a HVAC vacuum pump prior to refilling.
Having the system open will allow some moisture to enter from the air and this can become entrained into the flow and freeze in the orifice tube or expansion valve.

The low vacuum "pull down" prior to charging will cause the moisture to evaporate and be sucked out of the system.

The R12 systems were very critical with moisture as any water when combined with the refrigerant will cause the formation of acids in the system that damage things.


Just how I do it.

MGW

 

[THEFERMANATOR]

To add onto what MGW said, it is PAG oil for 134 which is a synthetic and mineral oil for 12. 94+ are all PAG to begin with though. There is also ESTER oil which can be mixed with PAG or with mineral, but NEVER mix PAG and mineral oil. Also 134A is MORE critical that 12 to get the moisture out. When it first came out they said it didn't need to be vacuumed down, but after less than a year we discovered that this was false and that 134A reacts VERY badly to moisture in the system. Also in regards to the orifice expansion valve combo, do not go with an adjusteable orifice in the front A/C unit, you must stay with a fixed one if you want good performance from it. I tried that in mine before to get better cooling at idle and it helped at idle, but didn't cool for crap going down the road. And I highly reccomend running only the GM rear expansion valve as it is sized vith a different orifice than the aftermarket units so that it never completely closes off the refrigerant flow. The first valves did completely block off and they found that oil would puddle in the rear unit and eventually kill the comprerssor from lack of oil.

 

[Brooklyn Tow]

Missy are you related to GMCTD?.................LMFAO

 

[p38js]

thanks for all the insight I was able to put it on the machine today sucked it down made sure it held a vacuum for about an hour and serviced her up with 3.5lbs of R134A freon and ops checked good blowing icecubes out of the vents and the kids are complaining that it is to cold. (Perfect)