A/C is Trippin, all pressures fine according to shop

[SPD TRP]

Tryin to find the ambient temp sensor for the a/c.
TRSM says its by the hood latch infront of radiator.

Mine is a 91 and its not there, not even the wires are there.

Looking to test it because my a/c is trippin.

Blowing cool, take it to the shop, hooks up the gauges, all the pressures are fine, so I go into the inside of the car and that motherfu**er is blowing COOOLD. So I take off and it has been working great for about two weeks.

Well today I go to run it and we are back on that cool not cold program. A few WTF's later and I get my TRSM out and want to start checking stuff. Get the DMM out and when I get to the Ambient Temp sensor, its not where it is supposed to be, so another WTF and here I am.

OH, another thing, sitting in the garage that motherfu**er is blowing coold again.

Like I said--"a/c is trippin".


Wayne

 

[Joel W.]

Mine is not where the TSRM show it,. But it is visible from under the front lip of the bumper, drivers side. hanging down in front of the intercooler.

 

[SPD TRP]

Hey man I appreciate your response.

Any ideas why it is trippin?

Wayne

 

[Joel W.]

Well, it is not really my area. lol .. But when the AC is on and it's not blowing cold air, is the compressor engaged or not?

 

[SPD TRP]

yeah, it is engaged

 

[Joel W.]

I would ask Jetjock, Sounds like everything is working as far as sensors and switches, I might guess the compressor is going bad. But this is just a guess.

 

[SPD TRP]

yeah, I pm'd him. Thanks

Wayne

 

[Joel W.]

45-50 on the low side.. That is why I prefer an HVAC shop to most auto repair shops as the auto guys don't do it enough to be good at it..imo

Great info Gary..

Edit: What should the low side be with R134?

 

[SPD TRP]

I've replied to your PM Wayne. You could be low on 134, have a blend door problem, a heater water valve that stays on or a bit of moisture in the system (it'll freeze in the TXV and cause erratic cooling). Could be any number of things. Check the sight glass for bubbles, you should see them only just after the clutch is disengaged. If you see them all the time add a little refrigerant at a time until they go away and vent temps drop. In other words verify the refrigeration system first and move on to the climate controls if needed.

And whomever told you 45-50 low side is OK should be slapped upside the head. A look at 134's pressure/temp chart will show you why:

http://tinyurl.com/hpdla

Thats a handy site for calculating all kinds of things btw...

Thanks loads Jetjock, your information is always appreciated.

Wayne

 

[pb92supraturbo]

JetJock,

Since you are the resident A/C expert, can I bounce a Supra A/C question off you? I'll PM you if you prefer . . .

I've replied to your PM Wayne. You could be low on 134, have a blend door problem, a heater water valve that stays on or a bit of moisture in the system (it'll freeze in the TXV and cause erratic cooling). Could be any number of things. Check the sight glass for bubbles, you should see them only just after the clutch is disengaged. If you see them all the time add a little refrigerant at a time until they go away and vent temps drop. In other words verify the refrigeration system first and move on to the climate controls if needed.

And whomever told you 45-50 low side is OK should be slapped upside the head. A look at 134's pressure/temp chart will show you why:

http://tinyurl.com/hpdla

Thats a handy site for calculating all kinds of things btw...

 

[Joel W.]

I don't know. :dunno: I would guess lower #'s..

Hate not knowing so I did some research and found this...

At 90 degrees ambient, for R134a systems, look for about 200- 220 Pressures on the high side and about 25-30 Pressures on the low side at idle, and at 1,500 RPM look for about 220- 230 Pressures on the high side and about 20-27 Pressures on the low side.

 

[bigaaron]

I don't think anyone mentioned it could be heat related, is the aux fan kicking on and do you have a good fan shroud and good fan clutch?
If the condenser is not getting cooled properly the ac will not get cold.

 

[Joel W.]

Joel: That's right but you cheated .

Well, I admitted I did not know. LOL By cheating if you mean taking 2 mins to type "R134A low side" into google and hitting the search the web button.. Then yup.. I am a cheater.

"I can not help myself, when it comes to helping myself"

 

[Joel W.]

Naw, your not wrong. You banged on me once for being lazy, (which I was) lol, so I figured I would try actually looking this time for the answer.

Thank You!

 

[Nick M]

Step one is put a thermometer in the vent and see what the cycle temp is.

 

[pb92supraturbo]

Here’s my (long)story:

My Supra’s A/C system had been converted over to 134a by the previous owner. The conversion was done at a Toyota dealership and appeared to be done correctly. When I purchased the car, the A/C system was working properly and I didn’t think anything about it. There appeared to be a slight leak around a line connecting to the receiver(drier), so I decided to put on new o-rings and replace the receiver while I had the system open. I buttoned everything back up and evacuated the system for an hour and showed a reading of just over 30 inHG. I added 20cc of oil per the TSRM recommendation when installing a new receiver and also added a ¼ ounce of A/C system dye to help troubleshoot any future problems down the road. There is a 134a conversion sticker under the hood and it specifies the amount of refrigerant to put in the system. I added the specified amount of 134a as written on the conversion sticker on the car and the system works fine except for maybe on a 90+ degree day when the car has been sitting and heat soaking, and then it takes a bit for the system to cool down – what I would think is normal. The sight glass on the receiver shows bubbles when the compressor is running, even after a few minutes of run time to stabilize. I know that on an R12 system, the sight glass should be clear on a properly charged system when its running, but I’m not sure on a R12/R134a conversion. There are no leaks on my system since I replaced the drier/o-rings. I’ve reconnected my gauges and verified that the system is holding its charge. So should a R12/R134 conversion system sight glass be clear?

I dunno how much of an expert I am. There are guys here who do MVAC work for a living and I don't. I'm 608 Universal certifed though so that includes all forms of AC. Go ahead, I'll take a shot at it.

 

[3p141592654]

Bubbles in the high side are never good. You want a liquid coming out of the condenser.

As JJ mentioned, the right way to do this with a TXV system like the Supra's is to compute the subcooling. Take the temperature that corresponds to the pressure in the liquid line, and then subtract the actual temperature of the liquid line. The difference is your Subcooling. Typically its around 8 deg C.

The sight glass is a pretty good approximation but won't tell you if you are overcharged.

 

[pb92supraturbo]

I'll give it a shot(literally) . . . Thanks for the advice guys!

Yes. Add an ounce at a time until it's clear and then one ounce more beyond that. It's not uncommon to have to tweak a 134 conversion. You start with an initial 134 charge of about 80% of the R12 amount and tweak it from there.

 

[Adjuster]

I can attest to the need of a good working fan clutch.

My R12 system worked great at highway speeds, but would quickly shut down in traffic at the stop light when the hot air temps around all the coolers up there reached a point where the ambiant temps exceeded the shutoff point built into the system. (verified it was the ambiant temp sensor by isolating it with two stryofoam cups wrapped in tin foil for a moment, it promptly stopped shutting off at a stop, but then the temp started to rise on the engine... Not a good compromise.)

So, 65.00 and a new fan clutch later, it's working great, and has not shut off in traffic yet, and the car runs nice and cool all the time, highway speed, or stopped for mulitple lights with the AC blasting.

I think one possible reason the R134a systems are showing less ability to cool down your car's interior is because they can't cool it down as fast as the R12 it was designed for. (R12 is a better freon than R134a, so you need to design a larger capacity system to get the same cooling power of your "old" R12 setup.) My 94 Q45 was converted to R134a before I bought it, and on hot days, over 90f ambiant, the system has a difficult time keeping up in traffic. I've replaced the fan and clutch to no improvement. Also removed some of the air resonance chambers to get more air flow, but really it's just a symptom of the less effective Freon in a system not designed for it from the start. The Q is up for sale now, and the Audi I have that was designed for R134a has no problems at all, so it's just something our pre 94 AC will have to deal with as the supplies of R12 become more scarce. (Just go to Mexico, and buy all you want. It's nice and cheap down there too, but don't get caught bringing it back into the USA...)

Ok, I know this has to be a henweigh question, but what is a "TXV" system? (I know that automotive AC has the compressor, reciever/dryer, condensor, expansion valve and evaporator plus the limit switches to keep it all working right if there are problems, but what is a TXV?)