Temp Goes Up With AC

[David T]

If you filled it with the correct amount of refrigerant (2.2 LBS of R-12), the gauges will only tell you if you have non-compressable gasses and the low pressure switch settings. If it is cycling like it should you should be fine.

[JIMJAM]

People up N park during the brutal winters, I park during the brutal summers. My D has always hated summer and when all my issues pop up.
Once that stainless heats up, no break from the sun and parked on black top, the car cannot take it. I had to get accustomed to a engine that after shutoff can be burn your hand hot 4+ hours later.
Even with a upgraded radiator, custom fans, air dam to block fan heat from the tank, upgraded stainless bottle with 3 auto bleeds and a sensor that turns on the a/c fans sooner, my indicated temp on the dash has always hung betreen 220 and the next bottom line. Over 90 and real sunny the needle sits just under the 220. Threw all this money at it and that where it still sits even with all the mods.

Thats been my "normal" temp for 20 years and seeing that the engine hasn't melted either the gauge is wrong or the car can operate at that temp. Now if it starts touching that line and I am highways speeds, ok... But if I run across a traffic jam it's time to park under a overpass which I have done.

[JBaker4981]

Following up!

My car is still experiencing this issue. At our Tech Day last weekend, we replaced the low pressure switch (DGo) and dialed it back a full rotation counter clockwise as per their instructions for R134a. We verified that my system was not overcharged but undercharged so we added enough to verify that both High and Low sides were within spec with the ambient temperature that day.

While the AC is super cold and a blessing, my car still wants to overheat with the AC on while on the interstate/highway.

Now... On these early summer days with the outside temperatures being ~85F, I can drive the car around town, sit in traffic, and drive normally like any other car without issue with the AC running. The temperature gauge stays at the quarter mark in these scenarios.

But... If I hop on the interstate or a highway where I am driving consistently above 55mph with the AC on, then the temperature gauge starts creeping up to 220.
2022-04-24 15.49.53.jpg

When it gets close to 220F, I can turn it off and it will gradually creep back down to where it likes to sit. (Picture below is after it started creeping up once I turned the AC back on, but you get it)
2022-04-24 16.05.45.jpg

With the AC off, even on a HOT day like 90-100F (example such as last summer), the car stays cool.... around the 175F range. No joke - it sits a needles width above the first white line on the gauge. With that said, I think my cooling system is working well and the culprit has to be the AC system. (Picture from a hot September 2020 day)
40k Miles.jpg

I am currently rocking:

• DPI 2-Stage Aluminum Radiator
• DPI Fans
• Rebuilt Water Pump
• R134a Conversion
• New Low Pressure Switch
• AC Compressor - Unknown Model (IE Not Sanden)

Fans, Radiator, & Condenser below
Screenshot_7.jpg2020-02-27 17.41.52.jpg2020-02-27 17.42.09.jpg

Anyone have any thoughts? I would like to get this sorted out and actually enjoy the car with Summer rapidly approaching and Ceramic Tint now on the car.

[David T]

It can get complicated because you need 2 systems to work well, the cooling system AND the A/C. I like to start with the cooling system. I see you have done a lot to upgrade the cooling system. There are some things you still can do. Check the timing, vacuum advance and mechanical advance of the ignition system. If it is not right the engine will run hotter than it should. Calibrate the temp gauge with an IR thermometer. Verify both fans run and are running in the correct direction. Make sure NOTHING is blocking the intake grill for the rad like a license plate. Test or replace the thermostat. See if any of this makes a difference. Once you can get the cooling system to run right the A/C system may not need any work.

[Bitsyncmaster]

With it running hotter with the AC on you have verified that the problem is not the otterstat since the fans run all the time with AC on. Your air flow is the same over both the condenser and radiator so that is not the problem. But the AC pre-warms the flow over the radiator. So what I would do is a flush of the engine coolant with my guess you have poor heat transfer from the engine block to coolant.

Use a radiator type flush that removes contaminates and oxidation.

[Jason]

Maybe check for exhaust gases in the coolant?

My car would behave similar to what you describe. Normal temps with the AC off, but with the AC on and over 80 degrees outside the coolant temp would just slowly rise, even when driving at highway speeds. Turned out I had a head gasket leak that was letting some exhaust into the coolant which lowered the cooling efficiency just enough that it couldn't keep up when the AC was on. Other than the AC temp problem and that an exhaust gas in coolant test read positive there were no other symptoms.

[Ron]

What's bugging me here is that the thermostat shouldn't let the temp drop below 195° F, and, 220°F is acceptable.
Not to mention that the gauges are not known for accuracy.

But I have to agree with Dave WRT the cooling system being able to handle anything the AC can throw at it, and then some.

[FABombjoy]

What's bugging me here is that the thermostat shouldn't let the temp drop below 195° F (180°F if no converters), and, 220°F is acceptable.
Not to mention that the gauges are not known for accuracy.

On my car the temp gauge is very nonlinear after the first 1/4 mark when compared with the EFI temp sensor. This might be "solving the gauge" rather than "solving an overheat".

But I have to agree with Dave WRT the cooling system being able to handle anything the AC can throw at it, and then some.

As long as the ducting is installed and the fans running, for sure. I see that the plastic fan shroud has been replaced with metal, which I'm not a fan of (oops, pun). Is the original ducting still in place? My experience with fan shutdown at speed shows that passive airflow is bad, so all of the pieces really need to be there for things to work the best.

[FLUX @88]

I have the same issue, I am going to flush my coolant again as I noticed in the jar some crude. My radiator is also a year old... I have a feeling some crude has made it was in the radiator.....

[cis6409]

Maybe check for exhaust gases in the coolant?

My car would behave similar to what you describe. Normal temps with the AC off, but with the AC on and over 80 degrees outside the coolant temp would just slowly rise, even when driving at highway speeds. Turned out I had a head gasket leak that was letting some exhaust into the coolant which lowered the cooling efficiency just enough that it couldn't keep up when the AC was on. Other than the AC temp problem and that an exhaust gas in coolant test read positive there were no other symptoms.

+1 for me to.. - (IF all the other things check out like both fans working ETC) . The A/C making it go hotter seems to be more of a symptom not the cause. It's exposing a weakness in the cooling system by putting more 'stress' or load onto it that it can otherwise handle.
Hopefully it's not that for you good luck witb the investigating

Shane