A/C pressure switch problem

forango

Member
Feb 19, 2003
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south florida
I had an odd issue happen this weekend..I was working on my car's stereo system and was finishing up when I heard a decently loud POP and then air hissing. I thought my tire popped out of nowhere but it was under the hood. What I found was the the low pressure switch on top of the accumulator had literally popped off and the hissing was coming out of the port. The car is a '93 GT, but previous owner at some point converted to R134

I went to Autozone and got a replacement switch(for a 95 suggested by friend) and o-ring, but the switch will not tighten without "stripping" back loose again. I was able to tighten the original switch back down one time but the compressor did not turn on. I jumped the terminals on the connector and that turned the compressor on, so at least that is not dead. I am guessing the compressor will not come on because the accumulator vented all the 134 out? Although reading more I thought the valve on top was supposed to keep that from happening?

A couple other odd things...the a/c was not on at all the entire day this happened. I did have the car running for a good 15-20 minutes prior since I was working with my amplifier and didn't want to kill the battery. I have attached 2 pictures, one of which showing that one of the heater core hoses was actually resting against the top a/c line coming out of top of accumulator..could the heat from that have conducted heat into the accumulator to cause the pressure build up for this problem?
 

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The accumulator switch threads may be jacked up. The AC will not come on if the freon is low.

Do you have the shroud on your car ( plastic piece that bolts on the radiator and circles the fan) ? The fan clutch could be bad and radiator may have been getting hot. Heat will make the pressure go up but that hose wouldn't have caused that.

Check you fan. Should turn with little resistance when cold. After running the car and temperature builds cut it off and turn the fan....it should be hard to spin.
 
I will check the fan but I assuming it is fine..I had the car running in 95º weather for 20-25 minutes and the temp never got passed the r in normal but I will check that out.

As far as the switch threads, a brand new one shouldn't be bad right? Could I possibly be using the wrong year switch? I have no idea what year or what car this accumulator came off of....these are likely stupid questions, but I know jackcrap about a/c LOL
 
Here is a potentially stupid question...is there any difference in the accumulator used between r12 and r134? Just wondering if when they changed this car over they were cheap and kept old accumulator and maybe that is why the r134 switch isn't attaching properly
 
The drier (what you are referring to as an accumulator) is the same for R12 and R134A. The threads are probably just old and jacked up. Someone probably cross threaded it at one point. If I had to guess the shraeder valve got jacked up too. I'd go ahead and change that drier cannister. It's going to need gas at this point anyway.

Kurt
 
Here is a potentially stupid question...is there any difference in the accumulator used between r12 and r134? Just wondering if when they changed this car over they were cheap and kept old accumulator and maybe that is why the r134 switch isn't attaching properly
I think the drier/accumulator are common to both refrigerants, but the pressure switch is different between the R12 and R134.
 
I think the drier/accumulator are common to both refrigerants, but the pressure switch is different between the R12 and R134.
The pressure switch is adjustable so that it works with both R12 and R134. See the documentation below...

Here's some more help in the A/C arena...

Currently, I am running Enviro-Safe R12 substitute, and it works very well. eBay has 3 can package for $25 + shipping. It does not require any vacuuming or purging of the system, and is a real aid to the DIY guy looking to save some $$. The warning say it is flammable, but so is gasoline...

no matter what refrigerant you use, you will need to replace the accumulator/dryer; cost is about $55-$95


Try eBay for some R12, it is running $20-$30 a can. You need 3 each 12 oz. cans and 6-8 oz. of R12 compatible mineral oil. The R12 compatible oil is like $20 a quart when you can find it. You may be able to find a combination can of R12 and oil together which may be cheaper than buying a quart of oil..

It is illegal for a company to sell any refrigerant other than R134 to a person who does not have an EPA 608 or 609 certification. That includes Freeze 12. However, individual sellers like those on eBay and, not affiliated with a store often do not ask for any certification information, they just want prompt payment.

See http://www.epa.gov/Ozone/title6/608/overlap.html for more details


R134a Air Conditioner Conversion and recharge instructions


Revised 14-Jul-2013 to add Low Pressure Cutout Switch adjustments for R134 & Freeze 12

Color Legend:
R134 specific items and instructions are in red text
Freeze 12 specific items instructions are in orange text
Note: R12 is available on eBay. Use the Freeze 12 instructions except use the R12 36 oz refrigerant charge with R12 refrigerant
Items and instructions common to both R134 and Freeze 12 are in black text


Tools and materials you will need:

Gauge set for recharging = $20-$120 – check out the pawn shops for a bargain before you pay retail.
See Harbor Freight Tools for an inexpensive gauge set.

image_21674.jpg


Vacuum pump – I use an old refrigerator compressor = $20- $40 at used appliance stores, or go to the Dump and get one for free. Be sure to have some R12 compatible oil handy to keep it lubed up properly.
vacuum-pump1-jpg.jpg


O ring seal kit = $8.

Replacement accumulator/dryer assembly with hose $55-$75


Alternative refrigerant – Freeze 12 – it will allow you to skip flushing the system and reuse the original accumulator/dryer under certain conditions:
1.) If the A/C system has not been open to air for more than an hour or so.
2.) Or if it hasn’t out of refrigerant for more than 5-7 days and the system is till sealed up with no open or disconnected lines. You need to be able to hear the hiss when depress the valve core in either one of the service ports. That tells you that there is still pressure in the system, which keeps out moisture and contaminants.
If either of the above is not true, you must replace the accumulator/dryer assembly.

Freeze 12 refrigerant: $15-$16 per 12 Oz can on eBay. Get 3 cans, 2 for the initial charge and 1 spare for a top off charge.
Use R12 compatible mineral oil, 6-8 Oz. This may be difficult to find or expensive (~$20 a quart). Sometimes eBay will have the oil/R12 combination cans, which have about 4 oz. R12 and 2 oz. oil in them. If you go this route, add the R12/oil charge first, then add the cans of R12.
Do not use PAG oil in a Freeze 12 system without flushing it first.

Freeze 12 refrigerant charge= 26-28 Oz plus 6-8 Oz R12 mineral oil on an empty system. A recharge may only require 2-4 OZ of R12 mineral oil if you only replaced a line, hose or seals.


A/C systems that have had a compressor failure must be flushed. Failure to do so will result in the floating trash left behind from the compressor failure destroying the replacement compressor.

R134a = $11-$16 a can – takes 2 cans.

R134a PAG or Ester compatible oil = $7-$12 for an 8 oz bottle .

Pump to force cleaning fluid through the system $20-$50 (may use compressed air to do the same thing).

R134a charging adapter = $13 (I cut mine up to use it with the R12 gauge set that I have had for a long time).

Plastic tools to disconnect refrigerant lines - 1/2" & 5/8" = $4 each.

Flushing agent - Discount Auto Parts has some flushing solvent in a 1 gallon plastic bottle - try that first. Or use Mineral spirits = $4-$5 a gallon, tetrachloroethylene =$5-$10 a gallon, takes 2 gallons of either one.

Miscellaneous hoses and fittings to adapt the flushing pump to the system, and the R134a adapter to the R12 gauge set = $15.


R134 Refrigerant charge is 26-28 Oz plus 6-8 Oz of PAG 100 oil.

R134 Conversion Instructions:
I did a R134a conversion on my 89GT, and used all stock parts. You will need to replace the dryer/receiver (about $75 if you get the one with the hose made as part of the unit), and should replace all of the rubber "O" ring seals as well. You will need to drain all of the oil out of the compressor and replace it with new R134a compatible oil.

R134 instructions (skip this if you use Freeze 12)
Keep in mind that to fulfill the requirements of the EPA, you are required by law to recover any refrigerant that still remains in the system. How (or wither or not) you accomplish this is up to you. Connect the charging gauge hoses to the service ports on the A/C (red gauge = high pressure, blue gauge = low pressure) and open the valves on the gauges to dump the remaining refrigerant (if any) into your "Freon recovery system", whatever it may be. Disconnect the charging gauges since you are finished with them until you are ready to fill the system with R134a. Next comes the nasty part – in order to get all the old oil out of the system, you will need to flush it with special flushing solvent, or mineral spirits (ok) or tetrachloroethylene (better, but may be hard to get). If you leave the old oil in place it will congeal and reduce the heat transfer in the condenser and evaporator (read that it won’t cool good) and possibly damage the compressor.

Disconnect the compressor and remove it from its mount to flush it with cleaning solvent. Pour about a cup of solvent into the suction port and turn the compressor center hub about 10 turns while shaking the compressor to move the solvent around inside the compressor sump. Drain the flushing solvent out and continue to turn the center hub by hand to force out any remaining solvent. Then fill it with oil: add about 6-8 oz of the new oil to the compressor large suction fitting. Turn the compressor center hub about 20 turns as you turn the compressor face up and face down to distribute the new oil inside the compressor. Catch and replace any oil that comes out of the compressor.

Connect the pump (I had an electric sump pump I bought for $20) to the hose from the high-pressure side of the compressor. Alternately, you could use compressed air to force the cleaning fluid through the system. I didn’t like to do this since compressed air has lots of moisture in it, which is death to A/C systems. Pump the cleaning fluid through the system and let it come out the hose that was attached to the old dryer/receiver. I used 2 gallons of mineral spirits and pumped it all through the condenser and evaporator. The expansion valve is located near the firewall in the high-pressure line of the evaporator, and may cause the cleaning fluid to trickle through the lines at a very slow pace. You may want to pump cleaning fluid through the evaporator and condenser separately to speed up the process.


All refrigerant types
Next comes the changing of all the old "O" rings so that the chances for leaks is minimized. The new R134 compatible O rings are green colored, so be sure that the replacement O rings are green. Use the plastic connector tools to separate the lines, place the extended collar part of the tool so that it faces the large part of the connector and push inwards: this expands the spring so that you can pull the tube apart. You may need a helper to push on the tool while you pull on the tubes to separate them. Install the new "O" rings: be sure to coat them with new oil when you put them in. Install the new dryer/receiver, refrigerant service port adapter on the compressor, add about more 4oz of oil to high pressure line and tighten up all the lines. You may have to add more oil when you do a system that has been flushed or new R12 installation. The total oil charge should be 6-8 oz. for all types of refrigerants. Close the hood, start the engine, let everything get warm under the hood, but don’t add the refrigerant or turn the A/C on. Connect the charging gauge hoses to the service ports on the A/C (red gauge = high pressure, blue gauge = low pressure) and open both valves, then connect the center hose to the vacuum pump. The purpose of this exercise is to heat up the system so that when you vacuum it all down (yes, you will need a vacuum pump- mine is an old refrigerator compressor), that all the air, vapor and moisture from the cleaning fluid vaporizes and is removed from the system. Vacuum it down for about 30 minutes, this should give you about 28" of vacuum or more inside the A/C system. I have a vacuum gauge "T" connected into the vacuum pump line so that I can accurately watch the vacuuming process. This is a good time to take a soda and sandwich break since it doesn’t go faster if you watch it.

the R134a service fittings on the system: the red goes on the high side and the blue on the low side. This will help others identify that a R134a conversion has been done on the system.

Typical low pressure side R134 coupling
35-16363S-270x270.jpg


Typical high pressure side R134 coupling
35-16361s-270x270.jpg



Charging instructions for all refrigerant types:
Remove the electrical connector from the dryer/receiver and jumper the two connections inside the wiring harness side of the connector together: this allows the compressor to engage in spite of low pressure/no gas in the system. Close both charging gauge valves, and then disconnect the center hose of the charging gauges from the vacuum pump and connect it to the refrigerant can tapper. Put the refrigerant can in the can tapper and screw it down with the can tapper valve closed, then open the valve. Loosen the hose at the center connection of the charging gauge set until the refrigerant squirts out: this purges the line of air and moisture. The refrigerant is added through the low pressure side of the system, so open the low pressure gauge valve to add the refrigerant. Start the car and take note of the idle speed, then set the idle speed up to about 1200-1500 rpm, and turn the A/C on inside and set the fan speed on high. Watch for the pressure on the low side to drop off as you are filling, and the refrigerant can will get warm and stay warm. This tells you the current can is empty and needs to be changed for a fresh one. Before you disconnect the can, be sure to close the valve on the refrigerant can tapper.

Watch the high side pressure on the charging gages and regulate the adding of gas to keep the high side pressure under 350 psi. You will probably need a fan in front of the car to keep the readings below 350 psi. I had to put the refrigerant can in hot water while I was charging the system with it, or else the can got so cold that it quit flowing. Use caution when you do this so that you don’t get water in the charging adapter when you change the cans.

R12 Pressures when charging is complete
When you have added the 32-36 oz. of gas, the high side will read about 250-300 psi and low side about 28-38 psi. No adjustments need to be made to the low pressure cutout switch.


Freeze 12& R134 Pressures when charging is complete.
When you have added the 24-28 oz. of gas, the high side will read about 250-300 psi and low side about 18-28 psi.


Freeze 12 & R134 Low pressure cutout switch adjustment.
The low pressure cutout switches are adjustable. They should be set with the low limit about 18-21 PSI, the stock setting is about 25 PSI. Remove the wiring connector and there is a screw slot in between the connector pins. Turning it clockwise increases the trip pressure where it cuts off and counterclockwise decreases the trip pressure. I believe that each 1/4 turn counterclockwise lowers the cutoff pressure by 1 PSI.


After Charging refrigerant instructions, all refrigerant types
Turn the idle speed back to where it was, turn the A/C off, disconnect the charging gauges, and re-install all the caps on the service ports. Remove the jumper from the low pressure switch harness and plug it back on the switch connectors.

R134 only
Then put the R134a Service Sticker on, secure all the loose wiring on the system and you are done.

The typical sticker looks like this, yours may be different.



41-81359-270x270.jpg

I hope it cools good, mine doesn’t get quite as cold as it used to driving around town.

Thanks go to WWW.ACKITS.COM for some of the graphics.
Check out their website for parts and the Auto AC Forum.

The above technical note is for informational purposes only, and the end user is responsible for any damages or injury. The end user bears all responsibility for proper recovery/disposal of any R12 refrigerant.
I have EPA 608 and EPA 609 MVAC certification. And yes, you can shortcut the process, but there are negative factors if you do. Sooner or later, something will cease to function like it should. Shoddy work is a time bomb ticking away, waiting to explode.
 
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Don't get too complicated. Millions of cars have been converted from R12 to R134A without changing the cycle switch, or expensive components. I would gather from the pics that the the person who did the original conversion did not bother to change the drier, which is essential. The original drier is painted black as in the picture, and almost all the aftermarket ones are bare metal. If I were in the situation the OP is in, I would change the drier, and change the orifice tube. I would do a complete flush of the remaining lines, condenser and evaporator. I would drain the compressor, and replace the oil. Then I would vac and down and refill with R134A. If the OP happens to live close enough to me (North Georgia), I'd be happy to vac it down and refill it. I have more R134A than I am ever going to need.

Kurt
 
Wow thanks for all the replies...it is greatly appreciated.

Step one is obviously getting a new dryer..do I have to go with the factory 5.0 style(black), or can I go with the bare metal ones like LMR has for the 94-95? Only asking to be sure there are no fitment issues since it looks like the pressure switch comes off the side of the 95 style.

Also, is there any harm that can be done by waiting a couple weeks to get to these fixes? In the middle of trying to get a new house and just terribly busy with that stuff.
 
Wow thanks for all the replies...it is greatly appreciated.

Step one is obviously getting a new dryer..do I have to go with the factory 5.0 style(black), or can I go with the bare metal ones like LMR has for the 94-95? Only asking to be sure there are no fitment issues since it looks like the pressure switch comes off the side of the 95 style.

Also, is there any harm that can be done by waiting a couple weeks to get to these fixes? In the middle of trying to get a new house and just terribly busy with that stuff.
I bought mine for my ‘86 at Rock Auto, and it was black. Cheaper than LMR as well.
 
Wow thanks for all the replies...it is greatly appreciated.

Step one is obviously getting a new dryer..do I have to go with the factory 5.0 style(black), or can I go with the bare metal ones like LMR has for the 94-95? Only asking to be sure there are no fitment issues since it looks like the pressure switch comes off the side of the 95 style.

Also, is there any harm that can be done by waiting a couple weeks to get to these fixes? In the middle of trying to get a new house and just terribly busy with that stuff.

A drier is a very simple piece, and you can buy it almost anywhere. I would not give that latitude of discretion for the purchase of a compressor. AC work is a time issue over money. The reward of cold AC will be a product of your effort, not the money you spend. Make sure everything is clean, do a thorough job of vacuuming it out. When you push the quick disconnects back together, make sure you have clean O-rings that are well lubed so they don't pinch.

Kurt
 
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I had the exact same problem once. Well it didn't pop out but leaked and drove me crazy. The oring on the lp switch can be a pain to get just right. I had a whole case of every imaginable size and just had to find one that fit correctly. The big problem though was the switch threads have to be the exact right one or they actually don't ever tighten up. Once i got got the right one and the correct oring I've never had it happen again. The oring that comes with any switch never worked. You have to use whatever you need to see the oring as it's being screwed in because it will mash out without you even knowing it. Crazy that it's that much trouble i know.