R134A help needed; 1998 Suburban.

On Tue, 18 Jul 2006 09:10:05 -0500, "Kevin" > wrote:

>
>"John Hermann" > wrote in message
...
>>I have a 1998 Suburban with the 5.7L V8 engine. My wife
>> has observed that the AC in this SUV is not quite as good
>> as my 1995 Blazer AC with a 4.3L V6 engine (it does very
>> well).

To be expected -- see below.

>> I bought the Suburban used, and had a mechanic
>> check/charge the system right after I acquired it (EBAY
>> purchase). From what I can tell, the system is working
>> just as good as the day the mechanic serviced the system
>> 4 years ago. But I have to agree with my wife that it
>> could be better. I have guages, and have measured the
>> high and low sides (while the AC was running on high/max)
>> as follows:
>>
>> High Side: About 135 PSI (might be flucuating slightly, but not sure).
>> Low Side: Flucuating between 52 and 54 PSI; mostly stays at 54 PSI.
>> Outside Temperature at time of measurements was 100 degrees F.
>> Air was blowing cool/cold, but not freezing cold.
>>
>> I don't know what the pressures should be for this system;
>> I'm hoping somebody could help me evaluate the system before
>> I take it to somebody for servicing/repair; that way I might
>> be able to tell if they know what they are doing, or if they
>> are tyring to rip me off.
>>
>> Thanks for any help, and Best Regards,
>>
>> John Hermann
>
>To start off with, the pressures will vary considerably depending on a
>number of conditions.
>For instance:
>High side pressure varies with ambient temperature, humidity, air flow
>through the condenser, compressor speed, and restrictions in the system.
>
>Low side pressure varies with in cab temperature, air flow across the
>evaporator, humidity, heat load on the vehicle, compressor speed,
>restrictions in the system,
>
>Here is one scenario that you might use as a guide:
>
>Start the engine and turn on the A/C system. Place the controls on Max A/C
>and high fan. Run the engine at 1500 rpms

Good point, of course. To my knowledge there are NO shop manuals for
any make of vehicle that specify AC pressures at idle

> for about 20 minutes with the
>vehicle out of direct sunlight and all the windows closed.
>
>Lets assume the ambient temperature is at 95F and the humidity is between
>60% and 80%.
>Lets also assume the radiator cooling fan is functioning properly and the
>fan clutch is not slipping. The condenser and radiator fins are clean. No
>air dams or fan shrouds are missing. The engine is not overheating.
>
>We will also assume the A/C blower motor is functioning properly and none of
>the plenum blend doors are leaking or stuck.
>
>At this point the temperature inside the cab should have stabilized and the
>air temperature at the vents is as cold as it will get during the
>performance test. That should be somewhere in the neighbor hood of 45F

Going down the road the vent temperatures are typically 5-8*F cooler
under severe heat loads than at a stop.

> with the fan on high and checking the temperature at the vent closest to the
>evaporator core. Even slight variations in ambient temperature humidity or
>air flow could affect the air temp as much as 10 degrees either way.
>
>While the engine is still running at 1500 rpms and the compressor clutch is
>engaged. The low side gage should read between 26 and 42 psi. and may cycle
>the compressor off occasionally.
>The high side should be between 225 and 275 psi. There again slight
>variations in conditions can affect the pressures quite a bit.
>
>If all these conditions are met then the system is probably performing up to
>specs. Keep in mind that any variation in the conditions will affect the
>pressure readings.
>
>Also consider that the Suburban has a much larger area to cool than the
>Blazer,

Suburbans have always been known for taking quite a while to cool down
inside. Here in Texas you see a very high percentage of them with
aftermarket window tint -- the blackest the law allows -- that was
applied in a desperate attempt to help out a struggling AC system.

> and they both have basically the same capacity refrigeration system.

And if you have a dual system and turn on the rear air the pressures
will be higher -- both suction and discharge-- and the front vent
temperatures will be higher.

Don
www.donsautomotive.com

>Hope this helps.

"davemac" > wrote in message
ups.com...
> Kevin, with a head pressure of 135PSI, he definitely does not have a
> condensor or fan clutch issue, at least not as a primary problem.
> Condensor issues will show with too high a head pressure normally.
>
> dave mc
>

I agree. I just mentioned some of the things that could cause readings to
vary, one way or the other.

On Tue, 18 Jul 2006 23:59:57 -0500, "Kevin" > wrote:

>
>"davemac" > wrote in message
oups.com...
>> Kevin, with a head pressure of 135PSI, he definitely does not have a
>> condensor or fan clutch issue, at least not as a primary problem.

He sure might have a weak compressor problem, however. On the other
hand, that doesn't jive with it getting down to 50* vent temperature.
Bottom line is the readings don't mean much without knowing ALL the
parameters.

Don
www.donsautomotive.com

>> Condensor issues will show with too high a head pressure normally.
>>
>> dave mc
>>
>
>I agree. I just mentioned some of the things that could cause readings to
>vary, one way or the other.
>

Okay, here's the latest; again, I appreciate all of the help/info
everybody is giving. First off, I don't know what I'm doing, so
I took the car to a mechanic and he hooked up the gauges and got
completely different values on the high side. At idle (800 RPM),
the readings we

Low Side: 54 PSI
High Side 290 PSI

He revved up the engine a bit and the pressures changed; I didn't
take notes, but he said things were looking reasonable.

He basically confirmed everything that has been discussed in this
thread about Suburbans being very large, and the AC's struggling to
cool them in such hot weather. We measured the temps coming out
of the vents to be 70 to 75 degress standing still, and dropping
down to as low as 65 degrees when driving around. He noticed
a bunch of dead bugs and debris in the condensor coils, so he
just blew it out with compressed air; that got the temps to drop
to as low as 55 degrees while were were drive around; outside temp
was 100 to 101. The mechanic noticed some noise coming from
the compressor, and suggested that some oil could be added to
reduce it; also there was evidence that some of the oil is
leaving the system because the compressor is a bit dirty/oily.
I priced a new compressor, and Oreily's wants $448 dollars; so that's
a major expense; I would not install a remanufactured compressor
if a compressor is ever needed.

The only thing I'm not sure about is the low side; from what I've
read on the internet, 40 to 50 PSI is typical. The mechanic seemed
to think that the low side was okay and suggested instead of removing
some R134A, that the system should be evacuated, add the oil and a new
orafice tube and recharge to the exact system spec (4 lbs 2 oz of R134a).
Of course this would cost hundreds of dollars to do.

Would lowering the low side by 5 or 10 PSI help with the inside air
temp in this 100+ degree weather we're having? If so, what value
should the low side be set at? Or is the low side already correct?
How much life should I expect to get out of my old compressor
(if I have the system serviced as suggested)? The noise he heard
didn't seem bad to me; I thought it was normal. I'm reluctant
to do the service as suggested because the mechanic could not guaranty
that the performance of the system would improve; it would be a
do it and see what you get thing; and the compressor could still
die in a year and I'd have the major and very expensive repair also.

Again, thanks to everybody helping out with this thread. Hopefully
the info will help others too.

Best Regards,

John Hermann

Don > wrote:
On Tue, 18 Jul 2006 23:59:57 -0500, "Kevin" > wrote:

>
>"davemac" > wrote in message
oups.com...
>> Kevin, with a head pressure of 135PSI, he definitely does not have a
>> condensor or fan clutch issue, at least not as a primary problem.

He sure might have a weak compressor problem, however. On the other
hand, that doesn't jive with it getting down to 50* vent temperature.
Bottom line is the readings don't mean much without knowing ALL the
parameters.

Don
www.donsautomotive.com

>> Condensor issues will show with too high a head pressure normally.
>>
>> dave mc
>>
>
>I agree. I just mentioned some of the things that could cause readings to
>vary, one way or the other.
>

Ok so that high side reading is VERY different from what you stated
initially. You can try spraying the condensor with water to see if you
get better cooiling. If you do, then you would have to start looking
at the condensor and fan/clutch. Evacuating and recharging it at least
may be a good idea since you may be slightly overcharged with these new
readings.

So I think people have brought up some good points here with regards to
the cabin size of the Suburban and the fact that you have rear air as
well. The suction pressure of 40 PSI sounds high to me and will affect
the vent temps, although I don't have a lot of experience with systems
using rear air. I still think you should be getting better vent temps
and it will probably take $$$ to fix it. The fact that your compressor
is noisy is most likely an indication that it is weak or damaged. It
may have been damaged by your rear air TXV flooding and returning
liquid to it. This is why I'm saying to look at that rear TXV as a
potential trouble maker.

good luck

dave mc

On 19 Jul 2006 15:03:31 GMT, John Hermann
> wrote:

>
>Okay, here's the latest; again, I appreciate all of the help/info
>everybody is giving. First off, I don't know what I'm doing, so
>I took the car to a mechanic and he hooked up the gauges and got
>completely different values on the high side. At idle (800 RPM),
>the readings we
>
>Low Side: 54 PSI
>High Side 290 PSI
>
>He revved up the engine a bit and the pressures changed; I didn't
>take notes, but he said things were looking reasonable.
>
>He basically confirmed everything that has been discussed in this
>thread about Suburbans being very large, and the AC's struggling to
>cool them in such hot weather. We measured the temps coming out
>of the vents to be 70 to 75 degress standing still, and dropping
>down to as low as 65 degrees when driving around. He noticed
>a bunch of dead bugs and debris in the condensor coils, so he
>just blew it out with compressed air; that got the temps to drop
>to as low as 55 degrees while were were drive around; outside temp
>was 100 to 101.

Sad to say, you probably won't get it a whole lot better -- maybe a
little..

> The mechanic noticed some noise coming from
>the compressor, and suggested that some oil could be added to
>reduce it;

Unfortunately, this is frequently done with no knowledge as to what
the oil level really is. Excess oil does not help a compressor and,
in fact, makes it work a lotharde as it is not compressible. Excess
oil will reduce cooling.

> also there was evidence that some of the oil is
>leaving the system because the compressor is a bit dirty/oily.
>I priced a new compressor, and Oreily's wants $448 dollars; so that's
>a major expense; I would not install a remanufactured compressor
>if a compressor is ever needed.
>
>The only thing I'm not sure about is the low side; from what I've
>read on the internet, 40 to 50 PSI is typical. The mechanic seemed
>to think that the low side was okay and suggested instead of removing
>some R134A, that the system should be evacuated, add the oil and a new
>orafice tube and recharge to the exact system spec (4 lbs 2 oz of R134a).
>Of course this would cost hundreds of dollars to do.

It should be only a couple hundred or so.

>Would lowering the low side by 5 or 10 PSI help with the inside air
>temp in this 100+ degree weather we're having? If so, what value
>should the low side be set at? Or is the low side already correct?

That depends on how long the system was running and if the rear AC was
turned on. The longer it runs and cools down inside the vehicle the
lower the low side pressure will be. Its best to evaluate with the
rear AC turned off so that it bewhaves like a front only system. The
rear has an expansion valve which close with no airflow through the
evaporator.

>How much life should I expect to get out of my old compressor

They don't hold up well at all in these vehicles.

Don
www.donsautomotive.com

>(if I have the system serviced as suggested)? The noise he heard
>didn't seem bad to me; I thought it was normal. I'm reluctant
>to do the service as suggested because the mechanic could not guaranty
>that the performance of the system would improve; it would be a
>do it and see what you get thing; and the compressor could still
>die in a year and I'd have the major and very expensive repair also.
>
>Again, thanks to everybody helping out with this thread. Hopefully
>the info will help others too.
>
>Best Regards,
>
>John Hermann
>
>Don > wrote:
>On Tue, 18 Jul 2006 23:59:57 -0500, "Kevin" > wrote:
>
>>
>>"davemac" > wrote in message
roups.com...
>>> Kevin, with a head pressure of 135PSI, he definitely does not have a
>>> condensor or fan clutch issue, at least not as a primary problem.
>
>He sure might have a weak compressor problem, however. On the other
>hand, that doesn't jive with it getting down to 50* vent temperature.
>Bottom line is the readings don't mean much without knowing ALL the
>parameters.
>
>Don
>www.donsautomotive.com
>
>>> Condensor issues will show with too high a head pressure normally.
>>>
>>> dave mc
>>>
>>
>>I agree. I just mentioned some of the things that could cause readings to
>>vary, one way or the other.
>>