Overheating issues

[CyFi6]

Do you have a recommendation of how to best measure the condenser outlet temp? I was never able to get a good reading when i was trying to figure out either my sub cooling/superheat. How far after the condenser should it be measured, I was thinking at the liquid line going into the firewall(also hard to get a good reading with exhaust heat right there)? My Raytech IR thermometer proved to be extremely inaccurate and difficult to get aimed properly. I have a thermocouple probe but I was never able to properly get it to touch the line and give me a good reading. Depending on how hard I pressed etc it would change the reading, do you know of any good way to attach the thermocouple? Would a hose clamp work? Another issue was the fact that the high side port is all the way at the front, so i cannot monitor my pressure readings while in a real life situation(driving, gauges taped to windshield..it just wont reach). Best i can do is park the car in the sun, pop the hood and hook up the gauges. I cannot recall my pressures when doing this (will retest in a month or so when things warm up), but i remember high side pressure climbing until it reached a high enough pressure to cut out the compressor.

Purely by feel (not sure how much that is worth), i can tell you with certainty that the suction line directly from the firewall was warm whenever my vent temps were warm, and the compressor would run continuously, unless it cut out from too much high side pressure (never cut out from low evap temps at low speed/warm vent temp situations). When vent temps dropped, the line got increasingly colder. Heater was bypassed so that is a non issue.

Thanks for the help, it is appreciated!

 

[Nick M]

Do you have a recommendation of how to best measure the condenser outlet temp?

A/C manifold gauge set.

 

[te72]

Blame global warming man.

Seriously though, about your comparison to a Chevy truck, considering how big your average truck/suv cabin is, it probably has a lot more capacity to remove heat... Are your windows tinted? I haven't seen anything on that in this thread (or may have missed it), but that will make a HUGE difference living down there. I tinted every one of the cars I owned down there, for that very reason. Nobody likes having to wear oven mitts driving...

 

[CyFi6]

A/C manifold gauge set.

You mean like reading pressure and comparing to a chart?

Blame global warming man.

Seriously though, about your comparison to a Chevy truck, considering how big your average truck/suv cabin is, it probably has a lot more capacity to remove heat... Are your windows tinted? I haven't seen anything on that in this thread (or may have missed it), but that will make a HUGE difference living down there. I tinted every one of the cars I owned down there, for that very reason. Nobody likes having to wear oven mitts driving...

That is true, i know that a truck is going to have a much bigger condenser and evaporator and everything, but if the claims are true, there are people running supra ac systems in Texas/Florida summer heat with no issue down into the low 50 degree vent temps high 40's even. Whether or not they are telling the truth I couldn't tell you, I have never personally been in a supra that had a fantastic AC system.

And ya my windows are tinted. They are as dark as I can legally go on the fronts and as dark as I thought was reasonable on the rears.

 

[jetjock]

I thought this was a thread about overheating the engine and not the driver?

I'd probably put the gages on it too but if the AC system passes the performance test show in the manual it's working.

With CFC12 mine delivered recirculated vent temps of around 42 with an ambient of 100 but not much humidity. That seems typical of the climate you're in.

 

[CyFi6]

I thought this was a thread about overheating the engine and not the driver?

I'd probably put the gages on it too but if the AC system passes the performance test show in the manual it's working.

Lol it was, but now I realize it was never overheating in the first place. On to the next issue...

I will put the gauges back on this summer, I can't remember the readings I got last summer, I will have to dig through some posts on the AC forums. My gauges don't have any shut off valves at the ends of the hoses so I need to get some otherwise I keep losing refrigerant every time i put the gauges on and off not to mention venting the R12.

With CFC12 mine delivered recirculated vent temps of around 42 with an ambient of 100 but not much humidity. That seems typical of the climate you're in.

Under what conditions (ex. vehicle speed/rpm, blower speed, time vehicle was run for, out in the sun or not etc)?

I can achieve vent temps in the low 40's in 100 degree weather in ideal situations.. If I am cruising at 70mph down the highway for a length of time I start to freeze my butt off, even on high blower.

If i leave my house from the cool garage, vent temps get cool, mid 50s maybe and start to drop when I reach a steady speed, maybe 45mph.

If the engine is hot, car sitting in the sun, everything heat soaked, forget about it. I wont see vent temps come down for 10-15 minutes, and every time I return to an idle the temps start rising (over 65).

Even if my engine has fully cooled, and I come out from work, car has been sitting outside in the sun, if I jump in and turn the AC on and let it idle a few mins before I leave, when I get home (2-3 miles away) vent temps maybe are down to 65 if that(warm all the way home, and rising if I come to a stop, this is on med blower, recirc). In other words...roll the windows down and enjoy the hair drier.

Running around town short distances from here to there, there's almost no point of turning the AC on as it will never cool me down with these type of trips.

 

[3p141592654]

You need to measure the line temps with sub-degree accuracy, so that means a decent thermocouple setup is a must. You need to place the thermocouple on the pipe, then wrap it in insulation so your hands are not touching it. I like to use that gooey thermal pipe wrap that some people call "monkey shit". You also need to measure the hi-side pressure at the same time as things drift quickly in a car A/C. Superheat is fixed by the TXV, so no need to measure that, especially since you replaced the thing.

My A/C works fine all summer long. Its not as hot as AZ here most of the time, but every so often we break into the 100s. I've been logging my ECU coolant temperatures now that I can datalog the factory ECU, and with ambient temperatures in the 70s, I never see coolant temperatures above 95C. Today on the way to work it was between 88 and 94 C the entire drive.

 

[CyFi6]

You need to measure the line temps with sub-degree accuracy, so that means a decent thermocouple setup is a must. You need to place the thermocouple on the pipe, then wrap it in insulation so your hands are not touching it. I like to use that gooey thermal pipe wrap that some people call "monkey shit". You also need to measure the hi-side pressure at the same time as things drift quickly in a car A/C. Superheat is fixed by the TXV, so no need to measure that, especially since you replaced the thing.

My A/C works fine all summer long. Its not as hot as AZ here most of the time, but every so often we break into the 100s. I've been logging my ECU coolant temperatures now that I can datalog the factory ECU, and with ambient temperatures in the 70s, I never see coolant temperatures above 95C. Today on the way to work it was between 88 and 94 C the entire drive.

Great info thank you. Never thought of using that sticky insulation wrap, i know what you are talking about, I will have to pick some up (can it be found at a hardware store?). Also, where should I measure the temp along the pipe, as close to the firewall as i can get or directly after the condenser. Would make more sense to me to be near the firewall but I just want to make sure.

Its been in the 80's lately (hit 90 a week or so ago) and I haven't seen my temp go above 200F either. Its a different story though in the blazing hot months. With AC on, I see the highest temps when coming to an idle after a length of driving on the highway, but any extended period of very low speed stop/go kind of driving and the coolant temps seemed to run up (last summer). At the same time, AC vent temps would also dramatically increase and sometimes cycle off.

When the time comes though (wont be long) I will be doing what I can to diagnose this AC system, of course we still come back to the issue of whether or not there is actually anything wrong with the system, or if it is just only capable of so much.

 

[Nick M]

Knowing how you like to tinker and over analyze, go read up on the ideal gas law. It covers several things related to pressure, temp, and volume.

 

[grimreaper]

Its hard to compare the mkiii systems to 20 year newer vehicles. I did this initially and finally realized there are way to many advantages or disadvantages per vehicle. Trucks usually have a ridiculous amount of air flow through the grill. Not to mention the motor is usually toy sized compared to the engine bay. Neither of which is the case in the mkiii. A proper electric fan setup would cool better at idle then a clutch fan( assuming airflow is the issue). I used to hold a 1500rpm "idle" at extended stop lights. Helped quite a bit actually. Slowly rev her up until you hear the clutch fan sucking the license plate off the car in front of you. Of course hook up the gauges and leave the hood open and there where zero issues with temps..

Even newer vehicles have limitations. The 3rd gen dodge rams have a "mini" yet thick ac condenser that is offset from the radiator. It has its own elec. fan and draws 0 air from the radiator. The 4th gen rams have the condenser in front of the radiator but also include a slim full radiator sized elec. fan along with the clutch fan. BMW m3's have clutch fans along with additional pusher electric fans.. The pushers are fully shrouded, IIRC they also have an additional electric puller as well.

Talk with jdub, doesnt he live in your region? maybe he has had to overcome similar issues?

 

[CyFi6]

Been in the low 90's lately, thought i would add that i have gone back to a completely stock gauge cluster, I think the less I know the better :icon_razz

AC is working pretty well so far, my only complaint is that when the car/engine is heatsoaked it takes centuries to get cold, though I can only imagine that this is normal.

 

[Backlash2032]

Just FYI.. In the manual it says that the car may overheat with the A/C on in stop and go traffic..

 

[Nick M]

My new stock radiator and working A/C system made the air so cold with temps in the low 90's, the wife asked me to turn the temp up a little.

 

[CyFi6]

Just FYI.. In the manual it says that the car may overheat with the A/C on in stop and go traffic..

Ya I actually saw that and laughed my ass off... More concerned now about the actual performance of the ac than I am about overheating.

 

[CyFi6]

OK so I got some numbers for superheat that don't make a ton of sense. This thread is now about A/C by the way.
I had my compound gauge hooked up while driving, and my thermocouple mounted to the suction line directly after coming out of the firewall.

Car was heatsoaked, about 100 degree ambient temperature. Turned on AC to high, recirc.
Drove around town for 10 mins, pulled into the gas station and let it idle for about 1 min.

Low side pressure - 40PSI
Vent temperature - 58 Degrees F and very slowly rising
Suction line temperature - 71 Degrees F and very slowly rising
Superheat = 33 Degrees F

Got on the freeway after filling up and took readings after about 10 mins, readings stayed consistent after more driving on the highway.

Low side pressure - 10PSI
Vent temperature - 45 Degrees F
Suction line temperature - 60 Degrees F
Superheat = 58 Degrees F

After about 35 mins of freeway driving, got off and drove home about 10 to 15 mins. Let the car come back to an idle and stabilize. By now the sun was basically gone and very little sun heat load coming into the car.

Low side pressure - 30PSI
Vent temperature - 50 Degrees F
Suction line temperature - 60 Degrees F
Superheat = 29 Degrees F

Anything above 2000 RPM and suction pressure is consistently right at 10 PSI. Freeway RPMs are 3000
Also, the whole drive home, about 40 mins with the AC on high/recirc, the compressor never cycled off once. If I put the blower onto med speed, the vent temps came down to 39 and the compressor would cycle.
Need some help on this one, 58 degrees of superheat sounds retarded.

Also, does anyone know where I can get a LONG pressure hose so I can watch my high side pressures/find my subcooling while I am driving?

 

[jetjock]

You're right. Doesn't make sense. Btw when getting in the car after the interior has been heated don't recirc.

 

[CyFi6]

Yeah, didn't mention it but I always roll the windows down and put it on fresh air for a min after I take off. Interior soaks up so much heat though it is ridiculous, I can drive around with the windows down for 10 mins and it's still hotter in the car than it is outside, I always use a sunshade too.

 

[3p141592654]

To me the data supports a blockage in the system somewhere. The TXV seems to have no control of superheat (assuming your outlet temp reading is not being polluted by ambient air especially when moving on the freeway). Also 10 psi is way low, I would have expected ~30 psi. The high side pressure should be low if its blocked. Typically would expect high side pressure to be 1.8 to 2.1 times ambient temperature. That means on an 100 degree day, with low-moderate humidity, we would expect to see between 200 to 250 PSI on the high side. If you are under this (not at idle but at cruise) then I would start to suspect your TXV is stuck shut, or the screen is clogged with dessicant.

You can join two lines together using a coupling barrel.

 

[Nick M]

Maybe he has an origianl TXV, and not one of the recalled units.

 

[CyFi6]

To me the data supports a blockage in the system somewhere. The TXV seems to have no control of superheat (assuming your outlet temp reading is not being polluted by ambient air especially when moving on the freeway). Also 10 psi is way low, I would have expected ~30 psi. The high side pressure should be low if its blocked. Typically would expect high side pressure to be 1.8 to 2.1 times ambient temperature. That means on an 100 degree day, with low-moderate humidity, we would expect to see between 200 to 250 PSI on the high side. If you are under this (not at idle but at cruise) then I would start to suspect your TXV is stuck shut, or the screen is clogged with dessicant.

You can join two lines together using a coupling barrel.

OK, right now my thermocouple is clamped to the line using a hose clamp, then the whole thing covered with a split rubber hose and zip tied shut. Maybe this isn't enough? I don't know where to get that sticky insulating goo you talked about before. It is also just hard to believe that there is a blockage considering every line and every flushable component has been power flushed. I have searched for cold spots on any lines and never found anything. Receiver is also brand new, less than 1 year old. I have pulled the evaporator several times and it has gotten a new TXV more than twice because it was suspected to be bad. I have the older style TXV (86.5, has remote sensing bulb) that was not under the recall.

I am going to do a couple things now... First I am going to make sure all my temperature readings are accurate. I'm going to test my thermocouple and vent thermometer. Next I need to make sure my pressure gauges are reading accurately. They are not the most expensive manifold gauges in the world so I want to verify this. Then, I need to get my hose extended and get my high side pressure readings and sub-cooling readings, then maybe we will have enough info to figure out what really is going on.

Maybe he has an origianl TXV, and not one of the recalled units.

Correct, it is the older style that I don't believe is affected by the recall.