An a/c question for all you experts... - TTORA Forum
 
LinkBack Thread Tools Display Modes
post #1 of 11 (permalink) Old 07-04-2009, 01:08 PM Thread Starter
Senior Member
 
Join Date: May 2009
Posts: 178
An a/c question for all you experts...

So I picked up a can of refrigerant today (w/ pressure gauge) because I was thinking my system needed a little pick-me-up. I hooked on to the low side and the pressure was hovering around 50-55psi. I know that is a bit high. Who knows how accurate the gauge is though...

So, I went back to the Haynes to read what they suggested you check for low symptoms. One was touching the two pipes going to the compressor. There was definitely a noticeable change in temp between the two, so that checked out.

The second was the viewing test. It said that if while the vehicle was running the refrigerant looked foamy, then you may have low refrigerant...EXCEPT if the ambient temps are very hot (its about 80 today, within what they suggest for ambient outside temp). So this got me thinking there was a possibility it was low, because it had that white, frothy look to it.

But, it also said that "With the proper amount of refrigerant, when the a/c is turned off, the sight glass should show refrigerant that foams, and then clears." This was also my case, which contradicted above.

My a/c seems to run and work fine. It blows cold, but then again I have been in some vehicles that blow COLD. I'm wondering if I can get more out of it. I know it's bad to have low refrigerant and too high of pressures, so I don't want to risk anything. Also, I have owned the truck for 5 years, and I haven't noticed the a/c getting any warmer.

Does anyone have suggestions or is this something that a 2.7 is weak on?
krashDH is offline  
Sponsored Links
Advertisement
 
post #2 of 11 (permalink) Old 07-04-2009, 02:04 PM
insert originality here
 
firebox40dash5's Avatar
 
Join Date: Feb 2005
Location: Coos Bay
Posts: 932
Send a message via AIM to firebox40dash5
Mine was pretty weak when I lived in NC. I also tried one of those cans, but never wound up putting much in to get it in the green on that little gauge. It helped some, but what really made a difference was cleaning up the radiator and condensor. They were pretty well coated with mud and crap, and the engine had been heating up more than normal. A good, careful spray with a pressure washer with a wide nozzle (anything less than about 15 degrees will bend the fins way too easy) from the front and from the engine side helped both the AC temp and the engine temp quite a bit.

Now with 105% more bent tubing.
firebox40dash5 is offline  
post #3 of 11 (permalink) Old 07-04-2009, 03:56 PM Thread Starter
Senior Member
 
Join Date: May 2009
Posts: 178
Ya I figured this much. I did take it to the wash and did a low pressure stream on it to get all the gunk off...so it's fairly clean. When I hooked the gauge up it getting into the yellow...so the pressure was at "warning level" Everything seems to be working ok though, just isn't as ice cold as I guess I'd like it for the summer heat, being a landscaper.

I guess since my refrigerant seems to be good, it's where it has to be for the time being...I don't want any higher pressure.
Any other input would be great.
krashDH is offline  
post #4 of 11 (permalink) Old 07-04-2009, 04:06 PM
Veteran Member
 
Toyasaurus's Avatar
 
Join Date: Dec 2004
Location: Little Elm
Posts: 787
How is the fan clutch? When was the last time it was replaced? Mine was as simple as replacing the fan clutch to move more air over the condenser.

The government cannot give to anybody anything that the government does not first take from somebody else. When half of the people get the idea that they do not have to work because the other half is going to take care of them, and when the other half gets the idea that it does no good to work because somebody else is going to get what they work for, that, my dear friend, is about the end of any nation. You cannot multiply wealth by dividing it.."
~ Dr. Adrian Rogers
Toyasaurus is offline  
post #5 of 11 (permalink) Old 07-04-2009, 04:21 PM Thread Starter
Senior Member
 
Join Date: May 2009
Posts: 178
EDIT: Upon further investigation, it's not the fan clutch. when the engine is warm it is NOT able to spein freely, there is resistance.

It's not exceptionally hot here in Mt, maybe 95-100 tops in the middle of the summer, but I like to have ice cold a/c. I guess I can try to poke around a bit more...

Seeing that my vehicle is a 99 and I don't think any of the fan assembly has been worked on, I won't rule it out.
krashDH is offline  
post #6 of 11 (permalink) Old 07-05-2009, 10:04 AM
Senior Member
 
Join Date: Apr 2009
Posts: 132
Quote:
Originally Posted by krashDH View Post
So I picked up a can of refrigerant today (w/ pressure gauge) because I was thinking my system needed a little pick-me-up. I hooked on to the low side and the pressure was hovering around 50-55psi. I know that is a bit high. Who knows how accurate the gauge is though...

So, I went back to the Haynes to read what they suggested you check for low symptoms. One was touching the two pipes going to the compressor. There was definitely a noticeable change in temp between the two, so that checked out.

The second was the viewing test. It said that if while the vehicle was running the refrigerant looked foamy, then you may have low refrigerant...EXCEPT if the ambient temps are very hot (its about 80 today, within what they suggest for ambient outside temp). So this got me thinking there was a possibility it was low, because it had that white, frothy look to it.

But, it also said that "With the proper amount of refrigerant, when the a/c is turned off, the sight glass should show refrigerant that foams, and then clears." This was also my case, which contradicted above.

My a/c seems to run and work fine. It blows cold, but then again I have been in some vehicles that blow COLD. I'm wondering if I can get more out of it. I know it's bad to have low refrigerant and too high of pressures, so I don't want to risk anything. Also, I have owned the truck for 5 years, and I haven't noticed the a/c getting any warmer.

Does anyone have suggestions or is this something that a 2.7 is weak on?
I just wrapped up my A/C install in my '03 yesterday, so I have some recent experience here.

At idle, my low-side was about 50psi. At the specified 1500 RPM, it drops to about 30psi. The manual says that at 1500 RPM, 86-95F abmbient, recirculation on, the low-side pressure should be to 21.3-35.5psi.

You say that the A/C is cold, but not COLD. What are your vent temperatures and ambient temperatures?

In my case, at idle I had vent temperatures of 60F. That lines up well with my low-side pressure of 50psi (54F) which should be the temperature of the evaporator. A five degree rise through the vents is believable with recirculation off and the fan on high.

On the road, I have vent temperatures of about 40F. That also lines up well with my off-idle low side pressure of 30psi or so (35F).

These were with ambient temperatures in the upper 70s.

Since my install was from scratch, I put in two 12oz cans of R134a. This is theoretically more than the system should have in it, but since you never get everything out of the cans and there is some lost to the hoses, etc, it works out about right. The system should have 19.4-22.9oz of refrigerant inside.

In operation my sight glass shows a cloudy liquid that completely fills the window. There is no sloshing or surging of the liquid. When shut down, the cloudy liquid bubbles then goes clear. I have heard from other A/C forums that R134a and PAG oil are normally cloudy in operation, so I believe this is normal. What should or should not be visible in the sight glass is a matter of much debate in the automotive A/C world.

Despite what the top-up kits would have you believe, there is no way to charge a system based on pressures only. They can tell you if the system is really, really low, but your low -side pressures will look "normal" from about 50% charge (mine looked "normal" with one can in the system) well up into over charged. As much as I hate to admit it, the only way to be sure about how much is in there is to recover the refrigerant and charge into vacuum.

I don't doubt that in many cases topping off improves the performance of the system, but since you don't know how much you need, can't control the temperatures and airflows enough to be able to use the pressures as any kind of a guide, etc. they are much more likely to result in an over-charged and poorly performing system.

In theory, A/C work is nicely scientific and precise. In practice it is almost black magic, even for the professionals.
jski is offline  
post #7 of 11 (permalink) Old 07-05-2009, 10:16 AM Thread Starter
Senior Member
 
Join Date: May 2009
Posts: 178
^ Good information thank you.

I am going to check my temperatures today.

From what I have gathered, if anything I would need a slight top off. Since it's not going to do too much for me, I will probably leave it as is and save up my money for my next few repairs, since I don't believe it's anything wrong with the system, just not as cold as I like. Pretty much all of the things to check for a "healthy" system have checked out, so until something really takes a bomb, I guess it's on to other projects.

Thanks again

99 Tacoma 4WD 2.7 5spd
K&N intake, magnaflow 18" catback, gray wire,
headers, Hella's, Fosgates, Kenwood deck
krashDH is offline  
post #8 of 11 (permalink) Old 11-09-2009, 01:05 PM
NorCal Chapter Pres
 
NorcalPR's Avatar
 
Join Date: Apr 2005
Location: In Cali
Posts: 12,141
Send a message via AIM to NorcalPR
Quote:
Originally Posted by jski View Post
I don't doubt that in many cases topping off improves the performance of the system, but since you don't know how much you need, can't control the temperatures and airflows enough to be able to use the pressures as any kind of a guide, etc. they are much more likely to result in an over-charged and poorly performing system.

In theory, A/C work is nicely scientific and precise. In practice it is almost black magic, even for the professionals.
What about checking superheat temps? Won't this tell you if the system is over/under charged?

Hi, my name is Phill, above are things I say
W6FTW

Do you live in NorCal? Have you checked out the NorCal Section located here? If not check in today!
NorcalPR is offline  
post #9 of 11 (permalink) Old 11-09-2009, 11:10 PM
Senior Member
 
Join Date: Apr 2009
Posts: 132
Quote:
Originally Posted by NorcalPR View Post
What about checking superheat temps? Won't this tell you if the system is over/under charged?
Sort of... haven't done too much with superheat and subcooling numbers before, so I may not have this quite right...

Toyota used a thermostatically controlled expansion valve (TXV) instead of a simple orifice tube. The TXV will attempt to maintain a preset superheat value by throttling the refrigerant flow. While this results in nice even evaporator temperatures under wildly changing conditions of compressor RPM, condenser and evaporator air flow, etc. it makes charging based on superheat difficult

An undercharged TXV system will be starved for refrigerant. This will cause the valve to open all the way, but the flow of refrigerant is so low that all of it boils off in the evaporator and the vapor temperature rises as it travels through the rest of the evaporator. This will result in a higher than normal superheat reading.

A properly charged TXV system will have enough refrigerant so the valve will not run out of liquid refrigerant. The valve will pick a nice setting that results in just enough refrigerant to fully evaporate as it goes through the evaporator. The TXV will do its best to maintain this condition even as the temperature of the liquid refrigerant and the evaporator change.

An overcharged TXV system will have more than enough refrigerant. The valve will simply clamp down on the flow and maintain the superheat that it is set for. Meanwhile, the liquid backs up into the condenser and reduces the effective area of the condenser. Up goes the high side pressures and down goes the efficiency of the system.

While superheat can work well for determining the charge in a stationary system with constant airflows across the evaporator and condenser and a constant speed compressor, I don't think that it works as well in an automotive setting with variable compressor speeds and condenser/evaporator airflows.

Subcooling supposedly can be used as a measure of the state of charge in a system as well, but since Toyota uses a receiver in the liquid line, you won't get an increase in subcooling until the system is severely overcharged and liquid is backing up into the condenser.
jski is offline  
post #10 of 11 (permalink) Old 11-11-2009, 05:11 PM
NorCal Chapter Pres
 
NorcalPR's Avatar
 
Join Date: Apr 2005
Location: In Cali
Posts: 12,141
Send a message via AIM to NorcalPR
Time will tell, but I was undercharged.

It was about 70 degrees today and I was comming out with 39degree vent temps while driving, with the recirc off

Before charging, I was pushing 44-46degree temps.

Hi, my name is Phill, above are things I say
W6FTW

Do you live in NorCal? Have you checked out the NorCal Section located here? If not check in today!
NorcalPR is offline  
post #11 of 11 (permalink) Old 03-09-2010, 08:37 PM
Urf
Senior Member
 
Urf's Avatar
 
Join Date: Nov 2009
Location: Palm Desert California
Posts: 118
Cool

I was complaining to a service tech buddy of mine about my a/c being weak, he took it in flushed it and checked it all out. Everything was perfect, except for my vent temp, he noticed the temp control in the cab felt sloppy so if you follow that under the hood on your fire wall some times you can pull that little valve closed a little further. I ended up replacing mine, it was like $25 I think, got the center vent temp while sitting in the shade down to 36 degrees. If I have problems again I'm gonna put a little 90 degree inline T-valve to furthur limit or shut off flow to the heater core.

04 4x4 LT X-cab 3RZ

"You're makin me look like a damn fool at the bar fights"- Early Cuyler
Said to his tatoo artist
Urf is offline  
Reply
Gear in this thread - Powered by O'Reilly Auto Parts

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the TTORA Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Another tire question for you "experts" KamoKid Tires/Wheels 3 06-27-2009 10:58 AM
a question for some experts. goldtaco112 Fabrication/Tools 6 02-24-2009 08:06 PM
Question for the experts! GoodyearMTR Tech 4 08-13-2006 10:47 AM
Question for all you Winch Experts acattaneo Early Tacoma Tech 2 12-30-2005 11:15 AM
GPS Question for the experts... Taco Madness Interior/Electrical/Electronics 3 06-06-2005 01:48 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome