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High Pressure on Low Side After Converting

sfrane on Sat July 26, 2008 5:31 PM User is offline

Year: 1992
Make: Mercury
Model: Sable
Engine Size: 3.8L
Refrigerant Type: R-132a
Pressure Low: 100

My A/C has been blowing intermittently hold & cold, then recently it started only blowing hot air. I took it to a local mechanic -- they discovered that the low side port Shraeder valve was leaking with no other obvious signs of leaks in the system. However, since it was an R12 system, they estimated about $350 just to recharge it, plus another $350 to re-charge it again if they had to replace something else to actually fix the problem. The mechanic suggested that since the R12 appeared to already have been nearly fully discharged from the system, it would make more sense to simply convert to R-134a. Well, after removing the remaining R12 and changing out the port fittings & Shraeder valves (per the mechanics instructions), I attempted to recharge it with R-134a. With the first can, the system charged up enough to activate the compressor, but it would only take about 3/4 of the can. I noticed the reading on the low side was around 100psi with the compressor running (I confirmed that the clutch was actuated and spinning). Admittedly, I was using one of the cheaper gauges, but it still was pretty clear that the pressure was much higher than it should be. I am mechanically inclined, but I have never done any A/C work before. Any ideas what is wrong? BTW, it is a Ford FS10 compressor (1992 Mercury Sable). Thanks!

TRB on Sat July 26, 2008 5:35 PM User is offlineView users profile

Minimum requirements for converting a system to R134a.

If system has any refrigerant R12 left in the system it must be reclaimed by an approved recovery machine.

Accumulator/drier must be replaced with an R134a compatible replacement. Conversion fittings and label must be added to the system. Label should have the amount of R134a used and quantity and oil type listed. If vehicle is not equipped with a high pressure cut off switch it must be added. That is the required minimum! While complying with the EPA laws may not provide the best performance.

Flushing the system to remove the mineral oil and debris should also be done. R134a and mineral oil do not work well together so leaving it in the system with R134a is not recommended! O-rings should be replaced with either NBR or HNBR replacements. Adjustment of the pressure cycling switch may also be needed to achieve the best performance. In some cases an upgrade of the condenser may be required to achieve the original performance. In many cases the parallel flow condenser will not be available as a direct replacement. Using a universal parallel flow is an option. A new custom hose set would be needed for the different style fittings used on the various parallel flow condensers.

There are many different suggestions when charging a R12 system with R134a. System must be evacuated before starting the charging procedure. I suggest you start with about 70 percent of the original R12 charge and add an ounce at a time until vent and pressure readings reach the best available results. Remember it is easy to over charge a system with R134a so patience is important.


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Evacuate and Charging Procedure.

Attach a/c manifold gauges to the vehicle. Make sure you attach the correct hose to the proper service port. This is very important to prevent personal injury! Attach center (Yellow Hose) to a UL approved a/c vacuum pump. Open both of the dials on you’re a/c manifold gauge set. This will allow the system to be evacuated through both the low and hide side of the system. Turn your approved vacuum pump on starting the evacuation process. 30 minutes usually will be enough time. If vacuum pump has ballast read the owners manual concerning this option.

When system has achieved a state of 29.9 hg’s of vacuum close both dials on the a/c gauge set. You may loose up to 1 hg for every 1000 feet above sea level depending on the capacity and quality of pump. At this point wait 5 to 10 minutes letting the vacuum boil off any moisture trapped in the refrigerant oil. This is also a good time to watch and see if vacuum has returned to a zero state. If so you need to check for leaks in the system. Assuming the system is holding a vacuum after letting the moisture boil off repeat the evacuation procedure again. This process may need to be done a few times before all moisture has been removed and you see no degradation in vacuum after closing both dials for 5 to 10 minutes.

With both dials closed remove the center charging hose attached to the vacuum pump and connect it to either a can tap and refrigerant or 30lbs refrigerant cylinder. Open the valve on either the can tap or 30lbs cylinder allowing refrigerant into the charging hose. With refrigerant in the charging hose slowly crack this hose at the manifold gauge bleeding off any air that may have gotten trapped when moving from the vacuum pump to the refrigerant source. Only the slightest amount of refrigerant should be released in this process so be sure to tighten the charging line quickly!

Open only the low side dial on you’re a/c gauges allowing refrigerant to flow into the system. Again I stress the high side must be closed or you may cause personal injury to yourself or others! Start vehicle and turn on the a/c system with blower on the highest speed. In some cases if the compressor clutch has not engaged you may need to by pass the low pressure cut out/cycling switch. Refrigerant should be charged as a gas but in some cases it may be necessary to charge as a liquid. Be careful not to slug the compressor with liquid refrigerant! Charge system to OEM amounts and pressures if you are using the refrigerant the system was designed for. If vehicle is has been or is being converted start with about 60 percent of the original charging amount. After getting 60 percent of the original charge slowly add an ounce at a time until you reach the best possible vent temperature and pressure readings. If you do not know what your systems operating pressures are you can use the 2.2 x the ambient temperature as a guide. This should only be used as a guide as many systems will need more or less refrigerant to achieve proper cooling.

Having a weak fan clutch or an inoperative electric fan will cause system pressures to be incorrect. So make sure these components are working correctly before charging a system!

In lower ambient climates, doors and or windows of the vehicle maybe required to be open to achieve proper cooling when charging the a/c system.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Chick on Sat July 26, 2008 5:39 PM User is offlineView users profile

Since it's an FX15 compressor..STOP! until you answer these questions..Did you change the accumulator, change the oil to one computable with R134a, and did you pull a deep vacuum and allow the vacuum to pull the refrigerant in before finishing the charge..If not, it's gonna fail, and the FX 15 most times require a firewall forward replacement of parts if it blows the insides thru the system..Let us know exactly what you did, and hopefully you didn't add R134a with sealers or other magic genies...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Chick on Sat July 26, 2008 5:40 PM User is offlineView users profile

Wow Tim, you were posting as I was typing..just like old times...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

TRB on Sat July 26, 2008 5:43 PM User is offlineView users profile

Just cut and pasted what was already in the tips forum!

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

sfrane on Sat July 26, 2008 7:05 PM User is offline

Thanks for the tips. I noticed you called out the FX15 -- I'm pretty sure mine is the FS10, but maybe they are similar/same. I specifically asked the mechanic if I needed to replace any components (ie, the drier) for a 134a conversion but he said no, so I didn't. He also indicated that if the system was empty of R12, I could just dump in the R134a without any further processes (such as vacuum purge) -- hence I didn't do that either. It sounds like I probably will need to do these to have a more reliable system that will last longer. I didn't get around to adding the oil charge yet -- the conversion kit instructions said to first charge with 1 can of R134a (I used Johnsen's 134a Refrigerant, which doesn't have any additives indicated on the can, so I don't think it has any of those leak sealers). After the first can of refrigerant, the kit instructions said to add the R134a oil (the compressor apparently won't actuate without the first can of refrigerant to reach the minimum pressure), but I didn't get around to adding the oil yet since the pressure was way too high.

Anyways, even if I didn't replace the drier and didn't apply a vacuum, would the system immediately have the symptom I encountered (100psi on low side with only 3/4 can of R134a added and compressor visibly running)? I could understand if the system ran normally for a while and then eventually gave me problems, so I really suspect that I had another failure to begin with that caused the A/C to go out originally. But I don't have A/C expertise so I could certainly be wrong.

Chick on Sat July 26, 2008 8:06 PM User is offlineView users profile

Yes, you did it wrong and you are going to have a big problem, take my word for it..There are no shortcuts in ac work, but there are very bad results.. First....

1. Find a new mechanic, yours obviously doesn't understand AC systems and how they operate

2. Don't use the system until you have what is in the recovered..

3. The refrigerant carrys the oil, and R134a doesn't move mineral oil.. The kit you are using is what we call "Death kits" they keep us very busy during the summer. Bring your car to a "qualified" AC shop and have them add the oil and vac/charge the system, as I said, those cars cool fine when properly converted..Just hope you didn't ruin the compressor by running it to long without the proper oil , and air in the system..Let us know how you make out..And CHANGE the o tube, inspect it for signs of black death..it will be apparent if it's there...Hope this helps..
Oh, and you can keep the accumulator provided it didn't suffer black death..In which case the system will need to be flushed of the contaminated oil..

Ford used the FX15 until 94, the FS10 took it's place, they look identical, and replacement you would use an FS10.

Here's a link to black death and believe me I've seen much worse O tubes... but this is what you have to look for...Fords with FX15 were the worse, FS10 replacement compressors are better, but low charge can still cause them to crap out...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Edited: Sat July 26, 2008 at 8:18 PM by Chick

CCWKen on Sun July 27, 2008 3:17 AM User is offlineView users profile

Yep, bad move and less than accurate mechanic. Even for just a drop in conversion you have to vacuum and add a different oil. The pressure you saw on the gauge was probably the pressure in the can at ambient temperature. As the rest have said, STOP! Otherwise, your mechanic is priming you for a major expense--Guaranteed.

You can't "check" the o-tube in these without cutting it out. It's sealed in the return line just after the flex hose from the evaporator. In fact, you can't even get to it unless you remove the entire line. Might just as well replace the line. And you have to be a contortionist just to get to the lower coupling on the firewall. That's with the accumulator out of the way!

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Ken Kopsky

Custom Car Works
"Rules are for the guidance of wise men and the obedience of fools."

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