87 Overheating with AC On

[MBDiagMan]

134A systems do seem to be somewhat sensitive to the amount of refrigerant used. When charging a system, you should use a scale, accurate to within 1oz. (or less) in order to charge the system correctly. Also, do not use or fall for those "hybrid" refrigerants claiming cooler temps than 134A, they usually raise system pressures and cause problems in the long run. Also, do not use the refrigerant / sealer junk, especially in a TXV type system.

CG

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There's LOTS of wisdom and good recommendations in this very short post!!!!!!!


I've been working on auto a/c systems since being in my Dad's independent shop at the age of 8 in 1957. He started installing aftermarket a/c systems and doing lots of a/c work.

Specifically for your C4, if you MUST change the earlier models to an alternative refrigerant, use nothing but 134. Charge by weight starting with 70% of the weight specified on the sticker found on the evaporator box. As George said, go up in 1 ounce increments from there.

My 88 was VERY happy with 70% of the sticker weight. It makes 36 degree vent temps and does it in a hurry even after it's red paint has been soaking heat all day in the Texas sunshine.

Not all cars convert well, but my Vette is probably the best conversion result I've ever had. Typically the later the car is before the industry changed to 134 in 93 or so, the better it will convert.

For cars that are not good conversion candidates, stay with R12. The price has come way down since the cars that require it have mostly left the road. For the most part only special interest cars are all that are left requiring it's use. Supply and Demand means that the lower demand is lowering the price.

When it comes to original R12 auto a/c systems there are probably more myths surrounding the subject than any other thing I can think of.

Again, we should thank George for the comprehensive post.

 

[Curious George]

I have a '92 convertible (and automatic to boot) and when I converted from R-12 to R-134A, I did not see any difference in coolant temps nor any other "anomalies". Typically, 134A systems are designed with a parallel flow condenser for maximum system efficiency. When converting a GM system (orifice tube type) to 134A the single biggest improvement comes from using a slightly smaller orifice tube assuming the rest of the conversion was done properly. For example, the factory o-tube in my '92 was .072". By using a Ford blue o-tube (.068") you can get better performance (cooling) from the R-12 designed system and old school condenser.

CG

One item I forgot to mention that will ensure you get the best performance / lowest vent temps when doing a conversion... is the low pressure cut-out switch. A lot of GM systems use a switch that is adjustable, some do not. If your switch is adjustable (to tell if it is, pull the connector off of the switch and look between the two contacts and you will see a small flat head screw) you will need a set of gauges connected in order to adjust the low pressure cut-off threshold to 134A specs. For 134A, if I recall correctly, I adjusted the low pressure to ~ 20-21psi. Turn the flat head screw counter-clockwise to lower the pressure, clock-wise to increase the pressure.

If your switch is not adjustable, you can buy a new switch (fairly cheap) already pre-adjusted for 134A.

CG

 

[boomdriver]

One item I forgot to mention that will ensure you get the best performance / lowest vent temps when doing a conversion... is the low pressure cut-out switch. A lot of GM systems use a switch that is adjustable, some do not. If your switch is adjustable (to tell if it is, pull the connector off of the switch and look between the two contacts and you will see a small flat head screw) you will need a set of gauges connected in order to adjust the low pressure cut-off threshold to 134A specs. For 134A, if I recall correctly, I adjusted the low pressure to ~ 20-21psi. Turn the flat head screw counter-clockwise to lower the pressure, clock-wise to increase the pressure.

If your switch is not adjustable, you can buy a new switch (fairly cheap) already pre-adjusted for 134A.

CG

OK, I have heard something about this before and I have a question...

When the system is charged, does'nt the low pressure cut out switch become a do-nothing part until there is loss of refriderant? Or is it the hi-press cut out that should be adjusted? I do not know exactly where my low cut out is set, but I DO know that it only takes about 1 lb to keep the switch closed and allow cycling. At 2 lbs the low cut out just does not take place any more.
When running, the normal system low pressure is closer to 45 lbs, so I'm curious as to why the low pressure cut out setting at around 20 would make any difference?

also, I am using the synthetic 134a right now and I agree that I'm another victim of slick marketing. I should know better.
The performance was BETTER with plain 134a, when I had a compressor that rattled and a system that was not evacuated !

I found my new orifice packaging today, and unfortunately it only has a part number on the tag...no size or other tell-tale. I think I will drain the system soon, replace with the "blue tube" and refill with plain 134a.
Another option is sucking up to my brother and begging some r-12 from his "stash" that he keeps in the back corner of his shop/garage....about 30lbs worth. Most people bought gold as an investment...not him, he saves refrideration gases.

 

[Curious George]

OK, I have heard something about this before and I have a question...

When the system is charged, does'nt the low pressure cut out switch become a do-nothing part until there is loss of refriderant? Or is it the hi-press cut out that should be adjusted? I do not know exactly where my low cut out is set, but I DO know that it only takes about 1 lb to keep the switch closed and allow cycling. At 2 lbs the low cut out just does not take place any more.
When running, the normal system low pressure is closer to 45 lbs, so I'm curious as to why the low pressure cut out setting at around 20 would make any difference?

also, I am using the synthetic 134a right now and I agree that I'm another victim of slick marketing. I should know better.
The performance was BETTER with plain 134a, when I had a compressor that rattled and a system that was not evacuated !

I found my new orifice packaging today, and unfortunately it only has a part number on the tag...no size or other tell-tale. I think I will drain the system soon, replace with the "blue tube" and refill with plain 134a.
Another option is sucking up to my brother and begging some r-12 from his "stash" that he keeps in the back corner of his shop/garage....about 30lbs worth. Most people bought gold as an investment...not him, he saves refrigeration gases.

Evaporator pressure (low side pressure) is directly related to evaporator temperature, just as high side pressure is related to condenser temperature. (It is more complex than this, but I have abbreviated the concept to keep it simple).

In order to test / set the low pressure cut-out you should do it when the outside temperature is not very hot / humid. Also, the fan speed needs to be set on LOW (recirculate), windows closed and doors shut to keep the cabin as cool as possible, so the A/C system can easily cool (absorb heat) the limited amount of air blowing through the evaporator. At this setting, the pressure in the evaporator will begin to drop and at a pressure determined by the low pressure cut-out, the compressor will cycle. For R-12, the pressure is about 24~25psi. If you adjust the low pressure cut-out too low, you can actually see the water that has condensated on the low pressure line freeze. If this condition persists for too long the evaporator will actually freeze and your cooling will go down because air is no longer flowing through the evaporator, but the air is blowing on a block of ice.

When it is hot / humid outside (and the fan speed is set to medium / high) you will not see low pressures as indicated above, but higher pressures as you indicated. Although the o-tube type system gets flack from seasoned A/C guys (they usually prefer the TXV system because it is more efficient and the compressor cycles less), I prefer it over the TXV. The o-tube system adheres to the brute force cooling method... The evaporator is flooded with refrigerant, whatever is not needed or left over (for example like when we are setting the low pressure cut-out switch) goes on to and gets collected in the Accumulator.

When the fan is on a higher speed, there is no refrigerant left over because it took every bit of refrigerant to absorb all the heat out of the air blowing through the evaporator. In this case, hardly any refrigerant is "accumulated" and it goes directly to the compressor to be turned into a high pressure gas again.

In a sense, the o-tube system only uses what it needs when the system demands are low, but when it is very hot out or the fan speed is on medium to high, it is b@lls to the wall.

CG

 

[boomdriver]

Evaporator pressure (low side pressure) is directly related to evaporator temperature, just as high side pressure is related to condenser temperature. (It is more complex than this, but I have abbreviated the concept to keep it simple).

In order to test / set the low pressure cut-out you should do it when the outside temperature is not very hot / humid. Also, the fan speed needs to be set on LOW (recirculate), windows closed and doors shut to keep the cabin as cool as possible, so the A/C system can easily cool (absorb heat) the limited amount of air blowing through the evaporator. At this setting, the pressure in the evaporator will begin to drop and at a pressure determined by the low pressure cut-out, the compressor will cycle. For R-12, the pressure is about 24~25psi. If you adjust the low pressure cut-out too low, you can actually see the water that has condensated on the low pressure line freeze. If this condition persists for too long the evaporator will actually freeze and your cooling will go down because air is no longer flowing through the evaporator, but the air is blowing on a block of ice.

When it is hot / humid outside (and the fan speed is set to medium / high) you will not see low pressures as indicated above, but higher pressures as you indicated. Although the o-tube type system gets flack from seasoned A/C guys (they usually prefer the TXV system because it is more efficient and the compressor cycles less), I prefer it over the TXV. The o-tube system adheres to the brute force cooling method... The evaporator is flooded with refrigerant, whatever is not needed or left over (for example like when we are setting the low pressure cut-out switch) goes on to and gets collected in the Accumulator.

When the fan is on a higher speed, there is no refrigerant left over because it took every bit of refrigerant to absorb all the heat out of the air blowing through the evaporator. In this case, hardly any refrigerant is "accumulated" and it goes directly to the compressor to be turned into a high pressure gas again.

In a sense, the o-tube system only uses what it needs when the system demands are low, but when it is very hot out or the fan speed is on medium to high, it is b@lls to the wall.

CG

Ok, thanks for the explaination.
I was under the impression that the low side port on the accumalator was as low as anyplace in the system and the reading of 45lbs there means that the entire low side was 45...but I understand the surges or waves in the system where the pressure at the evaporator could drop more as it travels, I had no idea that it could drop to half of what the low port showed.
I made the adjustment and will "test" drive later today. Its only 82* with 90% humidity right now, so its kinda chilly outside. I'll wait for 90/90 to put a decent load on the a/c system and see what happens.
I am wondering....my system did not cycle all that much. More so when the fan was set to a slower speed, (i think) but sometimes never when set on auto default 60* and under hi demand.

I still do not know for sure what orifice I have....The auto parts store could only tell me that the part that they gave me 2 months ago is what the book shows, with no alternative or no designation for r12 or 134a...The book only has the one part thats the same orifice for 84 thru 96, so the parts guy seems to think that it must be for 134a since everything was converted by the factorys by 93.
I question this because the parts mfg could not assume that older cars had been converted. I think its more a case of GM using the same orifice and changing other things to better suit 134a, like the condensor area and BTU ratings, making the system more efficient.I know that later model condensors were lots more efficient which aided in the heat exchange and relieved much of the system pressure.

Also, if it comes down to getting a Ford "blue-tube" orifice, is there a car model, yr to ask for? I mentioned this to the parts guy and he was lost....

Could this type of condensor (stock 87) be partially plugged inside.....thus forcing the gas to flow thru less veins making them hotter? I've read that some condensors will trap alot of debris from a compressor failure and hold the trash in the bottom tubes. This one flushed very well, and had nothing come out, but still, there is more heat than there should be. All the trash from my dead compressor was pilled up on the orifice tube and it took digging and some work with needle nose to dig the thing out. There must have been a thimble full of metal trapped on the orifice. That area got flushed 3 times...blown out backwards and forward.

I believe that my mediocre cooling (58 at best) and higher external heat is mostly from the junk synthetic 134a and the wrong orifice. It cooled better with plain 134a.

I found an interesting site that described all the alternative gasses that are available, none of which are EPA approved for use in mobile systems..yet. All are gas mixes that are not as good as r12 but better than 134a. Some are blends of r22& propane or some other flamable.
There was a welding supply company that had several home-brew gasses available...ironic.

I knew a commercial refridgeration guy in SoCal yrs ago that had some home-brew in his P/U that would create frost on the vents in the cabin...He serviced refeers trailers that hauled frozen foods, so he had the know how to turn his vehicle into a meat locker. Probably dangerous as hell, but interesting to witness.

 

[Curious George]

Also, if it comes down to getting a Ford "blue-tube" orifice, is there a car model, yr to ask for? I mentioned this to the parts guy and he was lost...

Ask the parts guy for a 1984 Ford LTD V8. This is the classic blue orifice tube (.067"). The "ears" that hold it into the low pressure line are slightly different than the GM o-tube, but it will work. I believe (my memory sucks for somethings, but I can remember the first grade!) I snipped the "ears" down a bit with my diagonal cutters and slipped it into the low pressure line. Don't worry, it won't go anywhere and you can get it out later for service if you need to.

Santech/A/C Orifice Tube | A/C Orifice Tube | 1984 Ford LTD 8 Cylinders M 5.0L 4BL HP | AutoZone.com

CG

 

[boomdriver]

Ask the parts guy for a 1984 Ford LTD V8. This is the classic blue orifice tube (.067"). The "ears" that hold it into the low pressure line are slightly different than the GM o-tube, but it will work. I believe (my memory sucks for somethings, but I can remember the first grade!) I snipped the "ears" down a bit with my diagonal cutters and slipped it into the low pressure line. Don't worry, it won't go anywhere and you can get it out later for service if you need to.

Santech/A/C Orifice Tube | A/C Orifice Tube | 1984 Ford LTD 8 Cylinders M 5.0L 4BL HP | AutoZone.com

CG

Thanks CG
it may be a couple weeks away, but I'll add that info to the list.
After spending some time with my head up in the nose yesterday, I'm now planning on a new condensor as well as the new 2 row alum radiator and the a/c system check-up.
The condensor at first glance seems to be in good shape, but there is enough small trash trapped in the veins to have some effect on the heat exchange. Combine that with the typical fin damage and there must be a 10% loss, at least. I've already wasted a weekend with a fin comb...and have no plan on doing that again. Its easier to replace if you;re already in there...its only $150 for a new condensor, even cheaper for some and a new one would be of current design, not circa 1980.:ugh

 

[raidoman]

Update on the 87 Rad Replacement

Got the 2 row and installed it. Temp dropped form 240+ to 217 max with AC on in Memphis traffic at 95 deg ouotside temps. When moving it runs in the high 190's to low 200's. Great improvement. Did have to do some mods on the shroud to clear rad cap, also opened it up for easier removal to clean out debris.
thanks for the suggestions.

 

[vettebob]

No wonder...

My first Vette, an '87. I just pulled the radiator to clean/service both it and the A/C condensor. HOLY COW!! No wonder everything has to be absolutely perfect for these things to not overheat. It has a tiny radiator that I would think would barely be sufficient for a Volkswagen!!

Looks like I'll have to buy one of those radiators mentioned in this thread as well... :confused

Thanks for the lead...
vettebob

 

[raidoman]

87 Radiator

The rad looks to be good quality and everything bolts up. A Dremel was handy to trim the upper and lower shroud to make large enough openings for petcock and had to trim for the rad cap. The rubber mounts need some trimming to accept the thicker rad. I also slotted the upper shroud by the upper hose to be able to remove it for future cleaning.

 

[MBDiagMan]

My first Vette, an '87. I just pulled the radiator to clean/service both it and the A/C condensor. HOLY COW!! No wonder everything has to be absolutely perfect for these things to not overheat. It has a tiny radiator that I would think would barely be sufficient for a Volkswagen!!

Looks like I'll have to buy one of those radiators mentioned in this thread as well... :confused

Thanks for the lead...
vettebob

This post surprises me. My 88, has stock radiator and condensor. The engine runs cool under all conditions and the a/c, even though converted to 134 can make a Polar Bear scream for mercy and I live in Texas.

 

[vettebob]

What temps does your engine run, both on the highway and in traffic with the A/C on during summer temperatures?

vettebob

 

[MBDiagMan]

In about any weather, on the highway it stays right around 192 to 195 and in stop and go wants to be about 210. With the exception of a time when it wouldn't warm up and needed a thermostat, it has always stayed in this temperature zone.

 

[vettebob]

Hmmm, interesting. Mine wants to run much warmer, and I have heard of so many that do so as well.

Thanks for the input,
vettebob

 

[MBDiagMan]

To be more precise, I watched temps closely when driving to work this morning. It is a 20 mile drive almost entirely on a winding country road with 55MPH speed limit until about halfway, then it goes to 60. Ambient was 78.

Coolant Temp climbed at a steady rate until it hit 195. Evidently the thermostat opened at this point and the temp went rapidly back down to 188, then crawled back up to about 190 and fluctuated between 189 and 192. I slowed down to 45 for about a mile where the speed limit goes down through a small village. When slowing down the temp climbed to 194 or so, assumedly due to lower air flow.

The oil temperature kept a steady climb and made it to about 208 before shutting it down on the parking lot at work. When I gradually slowed down for a turn, oil temp went down a couple of degrees.

I will check again in the heat this afternoon and add heat of the day results to this post.