A/C Head Pressure

[system-f]

I have replaced my expansion valve and re-O-ringed the entire system PLUS taken all the parts out and flushed with A/C system cleaner.

The problem: Not cold enough, 60 degree vent temp and seeing a steam (probably undercharged), problem gets worse when sitting still.

What kind of pressures should I be seeing with R134 on my 88 Accord?

(readings taken at 1000rpm with fresh air and high fan)
(Outside temp is around 100-102F. )

Condensor is clean, thinking about ordering that cross flow design?

Right now I am at 250/35 (actually 220/25 when I re checked tonight). Before I was at 274/40 (with almost 2 cans) and the A/C was cold, but for some reason would start to get too hot when the car was sitting still, vent temp of around 70 degrees. I have a 10" fan on the condensor and the stock main fan so there is tons of airflow over the condensor. I have read about the high head pressure with R134 and maybe I should go get a couple of cans of Freeze 12?

[system-f]

I'm pretty sure my problems are related the the inefficiencies of R134a. I have ordered some Duracool and plan to dump it in the Honda. if it works well I will convert my other two R134a vehicles.

[DBMaster]

I just replaced my compressor and the mechanic I trust told me his shop uses Freeze 12. The performance is acceptable with 43-45 degree vent temps on a 100 degree day. It seems to be almost as good as the R12 I was using up until three weeks ago. From the reading I did I learned that Freeze 12 is 80% R134a, but the other 20% (R142, I think) is what carries the existing oil since R134a won't. Unfortunately, I never watched vent temps when I was using R12 except for topping it off in the garage. I am thinking that it is a couple or three degrees higher now, but as alternative refrigerants go it is supposed to run lower overall head pressure that 100% R134a.

[system-f]

Thank you for the info, I read about your compressor failure. Freeze 12 still has a high head pressure when compared with a product like Duracool. Duracool maybe crap, I have no idea, but if it does half of what it says then I am sold. I just ordered it and hope to have it by the end of the week.

[DBMaster]

One of the guys on this forum used a homemade propane/butane blend with good results. I can't recall how long ago that was, though. I know it was at least three years ago. I supplied a brand new Denso compressor and drier to my mechanic due to time constraints, which is why I didn't just do the work myself. Since I supplied new OEM brand parts I allowed them to use Freeze 12 as it gives me a warranty on their labor. Danny (of Danny's Import Services) has worked on Hondas since 1978 and has always steered me right in the past so I decided to trust him on the Freeze 12. I do have three cans of R12 left at home, so I figured if I didn't like it I could purge it and recharge with Freon.

[Oldblueaccord]

Thank you for the info, I read about your compressor failure. Freeze 12 still has a high head pressure when compared with a product like Duracool. Duracool maybe crap, I have no idea, but if it does half of what it says then I am sold. I just ordered it and hope to have it by the end of the week.

look up duracool on the EPA website its propane.


235/ 40 sounds about what I remember. 275 on the highside sounds very high to me. Not sure why your only having 60 vent temps.


wp

[system-f]

It is propane with some other junk mixed in. Pure propane is an awesome refrigerant.

[Dr_Snooz]

You are way overcharged. Honda head pressures run pretty low. I think I run about 225 or so. You should only put two cans of 134 in. I am fairly confident this is not a 134 problem. You have something else going on, possibly as a result of overcharging it.

[skong]

I have the same problem. Low pressure is at 10 and Head pressure is above 250 and higher, center vent only blows 70 idle and 67 on high way. But i am using a kelin compressor converted to 134. The compressor leaks too, every months or so i have to recharge the system. I put 26 oz charge. but its free for me to charge it so i havent bought the nippo compressor. Cold enough for me to drive home from work on the highway.

[system-f]

You are way overcharged. Honda head pressures run pretty low. I think I run about 225 or so. You should only put two cans of 134 in. I am fairly confident this is not a 134 problem. You have something else going on, possibly as a result of overcharging it.

The readings I gave were with 1 and 1/2 a can from empty. I do not think this is over charged, but the expansion vavle could be trashed even though it is less than a year old. This entire system has been taken apart, re-o-ringed, new dryer, new expansion valve and cleaned.

Maybe Honda head pressures run low but from what I have read on the net 270-300 is normal head pressure for a properly charged R134a system. Both of my Nissan R50s run 300psi head pressure to properly cool with R134.

I added 1/2 a can tonight and the head pressure was at 250, outside temp was about 100, vent temp was 50 at 1200rpm.


I have the same problem. Low pressure is at 10 and Head pressure is above 250 and higher,

This sounds like a blockage of some sort. When my head pressure is at 250 I see at least 30 on suction. When I first bought my car the expansion valve was toast.

[Oldblueaccord]

If your vent temp was 50 and its 100 outside that might be about all you can get on our systems which I suspect are specced on the small side to begin with.

I do have tinted windows all around,louvers on the back hatch. I took apart my HVAC box and cleaned the coils out and sealed up all the connections. Most of the foam around the banding was missing.

I had guages in the past by they walked off and I never got another set. What ever setting I am at now are about correct but I am sure I put 2 cans in in early July and the system still had some charge in it.

My setups all original except a junkyard compressor I put in in 1995. I changed out most of the o rings except I guess the two by the expansion valve.


Did you vacuum the system down for a while when you refilled it ?



wp

[system-f]

Did you vacuum the system down for a while when you refilled it ?

Yes.

[stephensimmons]

Yes.

I got a dumb question but i have to ask it. Do you have the a/c clutch straight wired or is it wired through the pressure cut out switch and also dose your a/c clutch cycle? The reason i as is when i bought my car i had the same problem and someone had the a/c clutch straight wired and it had my evaperator freezing up because the clutch wasent cycling SO it wouldnt cool properly! And the problem was that the sun roof and the a/c clutch uses the same kind or relay(but they have two seperate relays) and i guess the one burnt out for the sunroof so they swaped them and straight wired the a/c clutch and that created MY problem! So check and make sure your a/c clucth is cycling properly and if not find out why and you may solve your problem.

[system-f]

When the temps are cooler out it does cycle or when I run it at night. On my last 3g I actually had a A/C switch that was bad. When it started to cycle it would cycle on and off very quickly and make the A/C clutch engage and disengage very quickly causing a shutter in the engine that took forever to figure out.

[Dr_Snooz]

Okay then, you're UNDERcharged. Anyway, I haven't seen too much clarity about head pressures on Hondas. The manual says to put X oz. of refrigerant in and that's it. After the 134 conversion, it comes out to 2 cans. It never mentions head pressures. They usually run low though. Fifty out the vent isn't wonderful, but like Old Blue says, you're probably about as good as you're going to get.

[system-f]

It is my understanding that head pressure is more a result of the type of refrigerant used rather than the system itself.

Anyways, I got my Duracool yesterday evening. The instructions for installing the Duracool refrigerant were:

1. evacuate the system
2. put a slight vacuum on it, 10in
3. Put the first can in and when it is done going in start the engine and turn the a/c on to suck the rest of the can in.
4. Install the 2nd can.

It was figured that I only needed 12oz of Duracool which is 2 cans (I may need more but only 2 cans are in now).

Last evening it was 95 degrees out. With the car idling at 1200rpm I was getting about 55 degree vent temps with FRESH air on and the fan on high...not great but still better than R134. The good thing is my head pressure was down to 210 and in this condition I would be near 300 with R134. I drove it around the neighborhood to get some air moving through the condenser and got the vent temp down to 50 degrees pretty fast.

On the way to work this morning vent temp didn't move above 40 degrees with the FRESH air open and fan on the 2 setting at highway speeds. I increased the fan speed to 3 and put REC on which did nothing for the vent temp. It is only 81 degrees out so this isn't a very good test. I have to do over 100 miles of driving today in REAL TX temps today as it is supposed to get up to 100 degrees.

The big difference I have noticed is the power used to turn the A/C (lower head pressure required to move the same amount of heat as R134). I can't really tell when the A/C is on or off. I keep a pretty detailed gas chart on my Honda and this summer the mileage has dropped from 30-32 down to 27-29 because of the constant A/C usage. My gas mileage chart will reflect any power savings with the A/C on pretty quickly.

I have 4 cans of Duracool left and at $9.99 a can it isn't that expensive. The plan is to put this stuff in my Infiniti QX4 which has a native R134 system. The Infiniti's head pressure sits right at 300psi. This system uses an always on variable displacement compressor which Duracool assured me is compatible. If it works good in the Infiniti then I will convert my Pathfinder (which is just a lower end Infiniti QX4...same A/C system)

[DBMaster]

Just don't put any stickers anywhere stating that you have used Duracool. It's illegal to use in an R12 system (item #4)... :)

http://www.epa.gov/ozone/snap/refrigerants/hc-12a.html

[Pnem3]

It is my understanding that head pressure is more a result of the type of refrigerant used rather than the system itself.

Anyways, I got my Duracool yesterday evening. The instructions for installing the Duracool refrigerant were:

1. evacuate the system
2. put a slight vacuum on it, 10in
3. Put the first can in and when it is done going in start the engine and turn the a/c on to suck the rest of the can in.
4. Install the 2nd can.

It was figured that I only needed 12oz of Duracool which is 2 cans (I may need more but only 2 cans are in now).

Last evening it was 95 degrees out. With the car idling at 1200rpm I was getting about 55 degree vent temps with FRESH air on and the fan on high...not great but still better than R134. The good thing is my head pressure was down to 210 and in this condition I would be near 300 with R134. I drove it around the neighborhood to get some air moving through the condenser and got the vent temp down to 50 degrees pretty fast.

On the way to work this morning vent temp didn't move above 40 degrees with the FRESH air open and fan on the 2 setting at highway speeds. I increased the fan speed to 3 and put REC on which did nothing for the vent temp. It is only 81 degrees out so this isn't a very good test. I have to do over 100 miles of driving today in REAL TX temps today as it is supposed to get up to 100 degrees.

The big difference I have noticed is the power used to turn the A/C (lower head pressure required to move the same amount of heat as R134). I can't really tell when the A/C is on or off. I keep a pretty detailed gas chart on my Honda and this summer the mileage has dropped from 30-32 down to 27-29 because of the constant A/C usage. My gas mileage chart will reflect any power savings with the A/C on pretty quickly.

I have 4 cans of Duracool left and at $9.99 a can it isn't that expensive. The plan is to put this stuff in my Infiniti QX4 which has a native R134 system. The Infiniti's head pressure sits right at 300psi. This system uses an always on variable displacement compressor which Duracool assured me is compatible. If it works good in the Infiniti then I will convert my Pathfinder (which is just a lower end Infiniti QX4...same A/C system)

Did the instructions say only 10" of vacuum or at least 10" of vacuum? You could probably have pulled down to 30" if you equipment will do it. I'm surprised that you are not getting cooler vent temps. What are your low and high side pressures? It's hard to say whether you are over or under charged. I'd have preferred to charge slowly while watching vent temps and pressure. If it turns out that you are over-charged then you will probably have to start from scratch and vacuum it out again. Check to see if your compressor is being turned off due to the thermal sensor near the evaporator. Mine would only cool to 40 degrees or so because that switch would turn off the compressor at too high a temperature.


One of the guys on this forum used a homemade propane/butane blend with good results. I can't recall how long ago that was, though. I know it was at least three years ago.

I did and have had fantastic results and no problems since.


Just don't put any stickers anywhere stating that you have used Duracool. It's illegal to use in an R12 system (item #4)... :)

http://www.epa.gov/ozone/snap/refrigerants/hc-12a.html

It is not illegal to upgrade or change the refrigerant in an R-134A system. As long as he changed the ports to R-134A ports he can label the system for the Duracool. He is supposed to have converted to the R-134A ports for the honest purpose of running R-134A in his system:D That is the only requirement.

[system-f]

The Duracool guys said 10in ONLY no more. Most of what I have read on HC refrigerants said no vacuum at all.

I think my expansion valve is toast or the sensor is not in the evaporator properly.


I'd have preferred to charge slowly while watching vent temps and pressure

This is exactly what I did. I got up to 210 on the high side and really didn't want to go higher. Pressures are more of a concern than vent temps to me for the safe operation of the A/C.


Check to see if your compressor is being turned off due to the thermal sensor near the evaporator. Mine would only cool to 40 degrees or so because that switch would turn off the compressor at too high a temperature.


I thought this was designed to prevent freeze up and would only turn the compressor off at too low a temp. Does it also work for high temps? I have had problems with this little switch before and might just need to replace it to be safe.


After another 50 miles of driving in 90+ temps I can honestly say I am comfortable now. Before with R134 my legs would start to sweat a little. Now even though the vent temp only gets down to 43 (in the outer most driver side vent) with the fan on high and REC on I am comfortable and do not sweat. The duracool does work better. I think colder temps are possible and I am not seeing the best conditions because of questionable parts functionality in my A/C system.

[Oldblueaccord]

Sounds like you got something to work out for you. Glad your staying cool again. Keep us posted on it from time to time.


wp

[DBMaster]

It is not illegal to upgrade or change the refrigerant in an R-134A system. As long as he changed the ports to R-134A ports he can label the system for the Duracool. He is supposed to have converted to the R-134A ports for the honest purpose of running R-134A in his system:D That is the only requirement.

Yeah, I read that after I posted the EPA link. That made me laugh for some reason.:rofl:

[Pnem3]

The Duracool guys said 10in ONLY no more. Most of what I have read on HC refrigerants said no vacuum at all.

I think my expansion valve is toast or the sensor is not in the evaporator properly.



This is exactly what I did. I got up to 210 on the high side and really didn't want to go higher. Pressures are more of a concern than vent temps to me for the safe operation of the A/C.



I thought this was designed to prevent freeze up and would only turn the compressor off at too low a temp. Does it also work for high temps? I have had problems with this little switch before and might just need to replace it to be safe.


After another 50 miles of driving in 90+ temps I can honestly say I am comfortable now. Before with R134 my legs would start to sweat a little. Now even though the vent temp only gets down to 43 (in the outer most driver side vent) with the fan on high and REC on I am comfortable and do not sweat. The duracool does work better. I think colder temps are possible and I am not seeing the best conditions because of questionable parts functionality in my A/C system.

What I was saying was that if your switch was bad like mine, it will turn your compressor off at 41 degrees (or what ever yours is doing) and your vent temps will never be cooler than that. If you hear that switch cutting on and off (you can hear it while you drive) and the vent temps are not near 32 degrees then your switch is bad.

As far as charging for pressures, it's possible to add gas and have your high pressure go down. This is because the system is cooling the refrigerant before it returns to the compressor. You should find that the high pressure is just fine and does not rise too high using this type of refrigerant. I'm curious as to your low pressure.

I'm not trying to make you wrong, but what I read on the Duracool website is this: After repair, continue with the charging procedure. Pull a vacuum of at least 25 cm Hg (10 in Hg). If a vacuum pump is not available be sure to use Duracool® DuraDry™ to remove system moisture. There seems to be some debate online between people that use hydrocarbons as refrigerants over how much vacuum if any to use.



Bottom line is that if you are happy with it then that is the most important thing.

[system-f]

How much in lbs R12 do our systems take? I charged my Infiniti QX4 with it tonight and it takes 1.43 lbs of R134 which converts to 8oz of Duracool. After one 6oz can of Duracool the Infiniti is super cold. I have 12oz of Duracool in the Honda which I am sure is too much. The infiniti's A/C system is much larger than the Hondas and I don't see it holding 1.43lbs of R12.

Nevermind found my answer 23-26oz of R12.

[Pnem3]

How much in lbs R12 do our systems take? I charged my Infiniti QX4 with it tonight and it takes 1.43 lbs of R134 which converts to 8oz of Duracool. After one 6oz can of Duracool the Infiniti is super cold. I have 12oz of Duracool in the Honda which I am sure is too much. The infiniti's A/C system is much larger than the Hondas and I don't see it holding 1.43lbs of R12.

Nevermind found my answer 23-26oz of R12.

The shop manual says 650-750 grams of r12 or 23-26 oz like you said. It is important to remember that this is a measurement of weight not volume. In other words, make sure you aren't using "fluid ounces" for any conversion. I think the chart on the Duracool site accounts for this.

Glad to hear the the Infiniti is ice cold. It has a better condensor than our cars and should be more efficient. Make sure not to under-charge it as under-charged systems are always cold but may not move enough oil to protect the compressor.

If you find that the 3Gee is overcharged then you will have to start from scratch with it because you cannot bleed off the combination of gases that
makes the Duracool without changing the blend.

[system-f]

Thanks for the info about the Duracool bleed-off. It does make me wonder how much of Duracool isn't just very pure propane and their special oil. I was just going to try to bleed off a couple of ozs, but it looks like I just blew $20.