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Old 08-19-2020, 01:07 PM   #1
Join Date: Jan 2016
Location: Edgewater MD
Default The great 240 AC system information dump + How to improve AC performance

This post contains an explanation of the basic function and issues associated with both early and late 240 AC systems, and guide for how to improve those systems. Dave Barton has a fantastic webpage https://www.240turbo.com/classicair.html with lots of good AC information, worth a read before diving into this post. My experiments/improvements have all been with a '91 240 with the later style AC system although the same information generally applies to both systems. I encourage others to share what worked for them and what parts they used. 240.kieth is working on upgrading his 1980 242s AC system so we may have an update for the early systems soon. My results so far have been fantastic with vent temps in the high 30s at idle with 85 degree ambient temps and high humidity.

Disclaimer Working on refrigeration systems can be dangerous. Over charging, clogged condensers, failed cycling switches and cooling fans can create very high pressures; to the point of rupturing hoses and causing serious injury. Great care must be taken when working with refrigeration systems. Venting refrigerants is very illegal in most countries, please be sure to properly evacuate and dispose of old refrigerants in accordance with your local regulations. Both R12 and R134A are known ozone depleting gasses. Most automotive shops can evacuate your ac system for a reasonable sum if you don't have the proper equipment.

The early system- 1975-1990

The early 240 AC system is a traditional style system with a receiver/drier on the high side and a thermal expansion valve (TXV). Single piston York compressors were used from 75-84, these are heavy and inefficient. 85-90 used a more modern rotary Diesel Kiki DSK-15BH compressor. All of these systems were designed to use R12 and Mineral Oil. Both evaporator and condenser are tube and fin units. All fittings and orings are SAE. High and low side service ports are located at the back of the ac compressor. The cycling switch is located on the high side, right next to the drier.
Even when they were new these systems didn't perform as well as most other cars, however there are things you can do to increase the performance of these systems. See the Improvements section below.

The late system- 1991-1993

In 1991 Volvo redesigned most of the 240s AC system. An improved HVAC box and larger parallel flow evaporator were added. Volvo ditched the TXV for a GM style orifice tube system with an accumulator on the low side. R12 orifice tube has a 0.072" orifice. Volvo also added a condenser pusher fan to help with ac performance while stopped or in traffic. This fan also ensures the high side pressures stay in check, without it pressures in the system can reach critical levels on very hot days. The fan is cycled via a pressure switch on the high side, it turns on at 247 psi and off at 188. A working condenser fan is a MUST for these systems. Unfortunately 91-92 systems did not have a high side service fitting, however if equipped with a Kiki compressor it may have both service ports at the back next to the suction and discharge ports. The low side service fitting is located on the accumulator next to the low pressure cycle switch. The cycling switch is set to 28 psi for 91-92 r12 systems. Fittings and orings are SAE on 91 and 92 models. The condenser is a tube and fin unit on 91-92 as well.
1993 is its own animal being factory R134A. The biggest difference was the addition of a much more efficient parallel flow condenser. Volvo also ditched the kiki compressor in favor of a more modern multi piston compressor with PAG oil. The orifice tube was changed to a 0.062" yellow GM unit. A high side service fitting was added to the high pressure line underneath the radiator core support. All fittings and orings are METRIC on 93s. The low side cycling switch is set to 23 Psi.

R12 vs. R134A vs. HC refrigerants

If you're unsure of which refrigerant you want to use please read this section. Having experimented with all three, hopefully my findings will help clear up a lot questions.

By far, R12 will work the best in any unmodified 75-92 system. The tube and fin condensers and evaporators(75-90) are not super efficient and rely on R12s amazing thermal conductive properties to remove heat. If your original system is just low on R12, by far your best option is to top the system off with R12. Out of all 3 refrigerants, R12 has the has the most mass(at the pressures used). This all translates to R12 being the most efficient refrigerant at removing heat from the inside of your car. Unfortunately R12 requires an EPA certification to purchase in the US (and its just plain illegal in some countries) so for most people this is not a viable option.

R134A can be made to work well in all 240 AC systems. Its very similar in mass to R12 however doesn't have the same thermal conductive properties. Ask any 1993 240 owner how their ac works and most of them will say fantastic. Properly converting your R12 system to 134A requires complete disassembly, some modification, and upgraded components to work as good as with R12 and be reliable. The benefit is any automotive shop will gladly service your ac and 134A is available everywhere.

HC refrigerants seem to be the center of a lot of debate. I'm sure some will argue their HC charged 240 blows plenty cold, however there are many variables. Products like Envirosafe, Frostycool, Duracool...etc These refrigerants are nothing more than dry Propane and Isobutane blends. I've heard of folks charging 240s with straight propane, which is a bad idea since most propane fuels are quite dirty and have some level of moisture, easy to contaminate your AC system. Not to mention the temperature pressure curve being completely different than R134A or R12, resulting in potential icing problems. These refrigerants are very sensitive to the charge ammount, a tiny bit too much or too little will make your ac not blow cold at all. All of these HC refrigerants have very little mass at the pressures used, meaning they will not remove heat as efficiently as R12 or even 134A. This is not ideal for an already undersized system. Another thing to note: No shop will want to touch that AC system after its been charged with HC. Certain types of leak detection devices will ignite the HC refrigerant(like... when looking for a leak...). Its illegal in most US states to charge your car AC with this stuff. These refrigerants exist because it IS legal in Canada where R134A is not available to the regular consumer. My experiences with HC refrigerant in an untouched (then later modified) 1991 240 R12 system were very disappointing as I could not get vent temps below 55 degrees, often taking 20 minutes or more to reach that temperature. Performance varied greatly depending on the temperature and humidity. I could never get cold air at idle. In order to get your system to work properly with HC, the system has to be in tip top condition, same as with R134A. If you're hoping to limp a weak system along with HC refrigerant, you will be very disappointed with the results. The only upside to these HC refrigerants is they are compatible with mineral oil and the original blue orings used in R12 systems.

R12 to R134A conversion information

There is a lot of misleading information about R12 to R134A conversions. The common belief is that you can just install some cheap service port adapter fittings and charge it up with 134A. This is almost guaranteed to kill your compressor as R134A will NOT mix with the mineral oil in the system. The compressor ultimately becomes starved for oil and disaster usually ensues. The old orings used in R12 AC systems will turn to mush in the presence of PAG oil and R134A, resulting in leaks. There are two ways to properly convert your R12 240 to R134A:

The first method is best for a system that was working correctly with R12 and the refrigerant leaked out, the compressor is not being replaced.

Step 1 is to replace all of the original O rings with green R134A approved orings. All R12 240s use SAE orings so one of those cheap assortments will have all that you need.

Step 2 is to replace the receiver drier(75-90) or accumulator(91-92).

Step 3 is to either replace the TXV(75-90) with the 134A version or to adjust the internal screw (Link to TXV adjustment thread: https://www.forums.turbobricks.com/s...d.php?t=213526)
On 91-92 cars the orifice tube must be changed to from the white one (0.072") to yellow (0.062").

Step 4 is to remove the compressor, drain the old mineral oil and fill the compressor with the correct amount of Ester Oil. Ester Oil is designed for conversions so it'll mix with R134A and wont react with any existing mineral oil in the system.

Step 5 is to install the 134A service port conversion fittings and vacuum down the system. Be careful not to charge the system with 134A cans have an oil charge or stop leak, as it will not mix well with ester oil.

The second method best if you are replacing the compressor. I highly recommend to replace your compressor as part of an R134A conversion because chances are your old Kiki compressor is very tired.

Step 1 is to disassemble the system and flush the hoses, condenser(if reusing) and evaporator(if reusing) using an approved AC flush solvent.

Step 2 is to replace all the orings with green ones.

Step 3 is to replace the receiver/drier(75-90) or accumulator(91-92)

Step 4 is to replace the TXV(75-90) with the R134A unit. You may adjust your old R12 TXV but if the system was contaminated at any point (compressor failure, system open and exposed to air for extended period) it should really be replaced. For 91-92 cars replace the orifice tube with the 0.062" yellow orifice tube.

Step 5 is to fill the compressor with the correct amount and viscosity PAG oil. The Sanden 4664 mentioned below comes shipped with a full charge of PAG 100 already in the compressor. Install the compressor.

Step 6 is to install the 134A service port fittings and vacuum down the system.

Special note for 91-92 systems: the low pressure cycling switch must be adjusted for proper ac performance with 134A. Attach your ac manifold to the low side. Locate the low side pressure switch on the accumulator. Remove the two wire connector. Located between both of the terminals is a flat head adjustment screw. In half turn increments, back the screw out counter clockwise. Plug it back in and turn on the ac. Rev the engine up to 1500 RPM. You should see the low side pressure drop until the compressor clicks off. The goal is to set this switch to cut off at 21 PSI The other option is to replace this switch with one from a '93 240.

Charge amount:

For R134A conversions, its recommended to use 80% of the R12 charge weight. This translates to:
1975-1990 Ac system R134A charge: 36.8 ounces
1991-1992 Ac system R134A charge: 31.2 ounces

However, in my experience slightly undercharging the system by a few ounces will give slightly better performance. Volvo lists the refrigerant capacity for the 1993 240 at 26.5 ounces even though the system is basically the same as the 91-92 cars. I recommend to charge 7-8 ounces less than the specs listed above and add more slowly, checking vent temps along the way. You should see around 30 psi on the low side at idle for all systems in good health.

Improvements to the 240 AC system

The efficiency and overall cooling capacity of a refrigeration system depends two main things: The efficiency of both heat exchangers(condenser and evaporator) and the compressors capacity. The number one complaint I hear about 240 ac is how there is a blatant lack of cooling at idle/low engine speeds. Granted there are a few different variables that can cause this issue, in the case of the 240 its usually a weak compressor.

The compressor problem

The biggest problem with any 75-92 240 AC system is the compressor. The York compressors used in the 75-84 cars are not good for anything other than R12. They are big, heavy and very inefficient. If you want to resurrect your 75-84, your best bet is to swap to the 85+ accessory bracket and swap to a modern rotary style compressor. The Kiki compressors used in 85-92 work decently when in good condition. As reported by many on here after 100K miles these compressors are usually worn out and wont make cold air until you rev the engine to 1500-2000 rpm. This can be confirmed with a set of AC gauges, high low side pressure and low high side pressure.

So what are your options for a replacement?

I purchased a "rebuilt" Kiki compressor off of ebay and was pissed to find it performed worse than the compressor I replaced! Come to find out, these units are NOT rebuildable.

Looking at ebay and amazon there are a couple different options, mostly Sanden 508 knockoffs. These are mechanically the same as the Sanden SD5H14 with 5 pistons and 138cc displacement. With the original kiki having 150cc displacement, these can leave much to be desired in the idle and low speed cooling department.

I've also seen a few different brands of rotary compressor that all seem to be based off of the Denso compressors. I have no experience with these, as usually run over $350. This is the same type volvo now sells at the parts department for your 240.

The solution: The Sanden 4664, a member of the SD7H15 compressor family. 7 pistons and 155cc displacement. These are smooth and quiet modern compressors that work much more efficiently at low engine speeds. They are used in pairs to cool FULL SIZE SCHOOL BUSSES My 240 rarely sees over 3000rpm so it makes sense to use a compressor that would be efficient at low speeds. I recently installed a Sanden 4664 in my 91 240 with nothing more than a 134A orifice tube, a 93 style parallel flow condenser, and ebay electric pusher fan. I was rewarded with CONSISTENT sub 40 degree vent temps whether at idle or driving down the highway. I haven't tried this compressor in an early TXV system yet, but I imagine the results would be similar if not better as the TXV actively regulates the low side pressure. One slight drawback: these compressors are shipped with PAG100. You must flush the system and replace all of the orings(as you should anyway when replacing a compressor) PAG oil is not compatible with R12.
240.kieth is currently working on installing one in his 1980 242 so we may have an update in the near future for the early systems. Cost for this compressor is $230 directly from Sanden but I was able to find one for $200 on ebay.

Heat exchangers

With a healthy compressor the efficiency of both the evaporator and condenser will need be addressed.

This is where the late system(91-93) really shines, the evaporator in these cars is absolutely YUGE! Nothing needs be done with these, they are already good working parallel flow units. The condensers on 91 and 92 cars are an area for improvement, they are tube and fin style units similar to those used in early systems (75-90) The solution is simple however, replace the condenser with the '93 parallel flow style. At the time of posting, these units are available from volvo or an italian seller on ebay for the hefty sum of around $400 us. Nissens still makes a replacement for the '93 240, the part number is 940422. These are available on ebay UK for about $200 us. If you are in the US and don't want to order from the UK I highly recommend contacting Nissens of North America, they will help you acquire one stateside. Another thing to note is the weak pusher fan originally used on these cars. I replaced mine with a $20 Ebay 14" reversible cooling fan mounted directly on the condenser. Even these cheap Chinese fans will move more air than the originals. Mine is wired into the existing fan circuit.

For Early systems (75-90) this is where things get complicated. Both condenser and evaporator are tube and fin units, however the evaporator isn't exactly small. Back in the 90s and early 2000s Volvo sold an R134A conversion kit for the 75-90 240. This is volvo Part# 9134808. It consisted of a bottle of ester oil, green orings for the entire system, an inline high side fitting, a low side adapter fitting, R134A TXV, and a special parallel flow evaporator. 240 owners who have installed these kits report good ac performance but these kits have been discontinued for several years now. The only option for getting one of these currently is to get lucky and find one in the junkyard. If anyone has one of these and would be willing to take some detailed pictures and measurements, please PM me. I deal with several different heat exchanger manufacturers at my job and could possibly have some made. Before you write off your existing evaporator, it still may be worth keeping. Due to its size the early evaporator can work well at lower fan speeds if the rest of the system is in good condition.
Upgrading the condenser to a parallel flow unit will also significantly benefit these early systems. Lowering the high side pressures through a more efficient condenser will lower the low side pressure- meaning colder evaporator temps. There are two different condensers used in 1990- cars. The first is the small early unit used in 75-1985 cars. These cars had different core supports than the later 86+ cars and consequently use a smaller condenser. As of right now there are no drop in parallel flow condensers for these cars, so the only option is installing a universal aftermarket unit. 240.keith has done this with success among several other members here. If anyone has a parts list for this please leave a comment!
1986-1990 cars received a larger tube and fin unit to take advantage of the increased room behind the grille with the later front end. There are bolt in parallel flow condensers for these cars available on ebay but again cost close to $400. A more recent search turned up this unit: https://www.ebay.com/itm/For-Volvo-2...kAAOSwsnhfMcpp
Which appears to be a parallel flow unit for significantly less money. I've messaged the seller to confirm if this is in fact a parallel flow unit.
75-90 240s were not equipped with a condenser pusher fan. Adding one will greatly improve ac performance at idle or in traffic. The cheap 14" ebay cooling fans are perfect for this. I wont go into details with the wiring here as there are many threads on the subject, but essentially you want to use a relay and wire the fan to come on with the ac.

Hopefully some of you found my ramblings helpful. Again, if anyone has anything to add please do! Ill be updating this thread when I have more information regarding the early systems.

Last edited by wcirco; 08-19-2020 at 03:13 PM..
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