I have looked through the archives and know the weights are there somewhere, but I can't find them.
I think Rob was the man with the knowledge, so maybe he can let me know.
Mine is a 1990 MasterAce Surf (CR30).
Dual air and cold box.
I recently had the system regassed with 134a.
It wasn't cold, only cool, and the relay behind the dash was chattering away - I think that means low pressure?
Since regassing, it now is cold, when you are up and running, but idling it returns to cool - but the relay is still chattering, and it is worse with both front and rear systems on. High revs and only one cooling component and the chattering lessens and sometimes stops.
My first thought is that they have not put enough gas in? Is that likely?
In that case I need to know the correct weight of gas, so I can check against the weight thay actually put in.
Also any other suggestions as to cause would be appreciated.
Thanks,
Dave.
- (#11963) DaveW, 24 Nov 03 23:06
Sounds like too little gas OK. The weights posted (I posted them some time ago) were for R12, the other stuff will be a bit different. 1200g for dual, can't remember about adding the coolbox- it's either the same, or about 1400g. Best way to verify is to have the aircon guy do it by the gauges...
- (#11964) david miller, 25 Nov 03 2:32
Thanks Dave,
I found your posts about that, and I am pretty sure the R12 was around 1400 for the triple system.
I seem to remember something about the 134a being about 80% of the weight, so I might work on that for now.
DaveW
- (#11965) DaveW, 25 Nov 03 4:09
Dave Miller's June 21 posting with R12 weights is in Ace Answers/Ace Handbook/Air Conditioning. 1600g with coolbox.
See http://www.mpvi.net/ia/pic.htm?pic=../im/rm289e92/ac/ac23volu.gif which explains how to interpret the sight glass regarding the amount of refrigerant, but refers to the single system (675g).
A/C fault-finding chart (still in two parts) ...
http://www.mpvi.net/ia/pic.htm?pic=../im/rm289e92/ac/ac18faul.gif
http://www.mpvi.net/ia/pic.htm?pic=../im/rm289e92/ac/ac19faul.gif
- (#11966) Dave (Sussex), 25 Nov 03 4:25
Thanks for that, all I need now is confirmation on the ratio for 134a.
I read a lot of the discussion, and Dave M's name was throughout, but I think Rob was the man with the ratio r12 to 134a.
It runs OK at the moment, but of course the idle is all over the place with the relay switching on and off - and it also can't be good for the compressor or relay to be continually switching.
I just have to check the papaerwork now and see if they recorded the amount, then call them.
Thanks again.
DaveW
- (#11967) DaveW, 25 Nov 03 5:23
Yes a word of warning for anyone having their aircon regassed. Tell them how much to put in.
The first time I took mine, I left it with the company and picked it up at the end of the day as they were also checking for a leak. I had to regas again this summer after almost 3 years. This time I found a one-man outfit who was very chatty (and much cheaper) and as he said there is no readily available data for these vehicles so if I hadn't supplied him with the figure of 1450g then he would have put about 950g in 'the going rate for this type of vehicle'. I wonder if that explains why my first regassing didn't last that long - low weight.
Incidentally I took the last of his R12 so couldn't comment on the weight conversion to 134a but I'm sure any technician worth his salt would know the correct weight based upon the figure for R12.
- (#11968) Ian Dunse, 26 Nov 03 4:06
Dave W, Yes I have done a lot of work on this subject myself, playing about with the weights to get the best efficiency. I have found that with our (dual system, no coolbox) it worked out at 1050 grams of R134a, that worked best, that's almost exactly 85% of the original 1200 grams of R12 it should have had. This would then mean that a triple system that would have had 1600 grams of R12 originally would need around 1350-1400 grams of R134a to work effectively. If you added the same weight of R134a as R12, it would over pressurise the system because R134a has more volume for it's weight than R12. See the chart at the bottom for the comparisons. The reasons it might not work too well at tick over is 1)The compressor is probably getting a bit tired & therefore not efficient at tickover. 2) The specific heat capacity of R134a is not as good as R12, therefore it does not as effectively move the heat from the evaporator to the condenser. 3)To do a retrofit properly you would need a condenser of around 20% bigger area to dissipate the heat.
Ian, if you had it last for 3 years then this is about right, inherantly a/c loses around 10-15% of it's gas each year (down to a pressure, then it won't lose much more) this could mean that you have lost 25% or more of your gas after 3 years, thus a loss of cooling effect, the a/c has to work hareder then & the fuel consumption goes up. Most vehicle manufacturers recommend a/c is serviced, with a receiver-drier every 2 or 3 years (vehicle dependent) so 3 years is to be expected.
R134a R12
Molecular weight 102.0 120.9
Boiling point (1 atm) oC -26.1 -29.8
0F -15.1 -21.6
Temperature glide oC 0 0
Critical temperature oC 101.1 112.0
oF 214.0 233.6
Critical pressure kPa 4067 4116
psia 590 597
Liquid density @ 25oC Kg/m3 1206 1311
Density of saturated vapour at 25oC
kg/m3 32.4 37.3
Specific heat of liquid at 25oC
kJ/kgoC 1.43 1.00
Specific heat of vapour at 1 atm & 25 oC
kJ/kgoC 0.874 0.606
Vapour pressure at 25oC
Hope this helps,
Regards Rob.
- (#11969) Rob Drinkwater, 26 Nov 03 14:46
I have 1991 Masterace and after three refils the aircon has worked for a while then given up. I have found some viscous brown liquid smeared around the top of the cold/hot box. Can anyone tel me how I can remove the box for either bypassing it or for inspection and possible repair. Having aircon is more important than a cool box should pinch come to shove.
Regards tew
- (#6944) Terry Withey, 27 Jan 04 03:38
The US toyotavan.org has an online workshop manual. It has an AC section which describes how to remove the hot/cold box. Getting spares for the box may be a problem. If you are thinking of just using it as a hot box, next time you have the gas removed, just get them to undo and blank off the supply and return pipes, you then have cool and hot box. If you have A/C on the cool turns to cold, if you select cold on the box, as the intake fan sucks cabin air into the box straight from the A/C out vent.
- (#6944) Clive (Bristol), 27 Jan 04 10:24
Different question, but same subject.
I find that when I start up from cold, the air con will not come on for a few minutes/or couple of miles.
I'm fairly sure it used to.
Wondered if its due to the cold weather in UK at the moment - ie: the sensor is cold enough already - or if it is a developing fault?
- (#6944) chris turner, 27 Jan 04 15:25
By definition A/c evaporators must not be allowed to go below about 3 degrees C, otherwise the water sitting on the fins will start to freeze, as water is at it's densest at 4 degrees, it starts to expand again below this (Hence the ice pushes the freezer door open!) If the evaporator ices up it will crack due to the expanding ice, the sensor on the evaporator will cut the a/c out @ 3-4 degrees C, hence yours doesn't work when really cold, it will almost certainly work OK once it warms up though. Still worth leaving on though as it will help de-mist when it does kick in, due to it helping to dessicate the incoming air.
Regards Rob.
- (#6944) Rob Drinkwater, 27 Jan 04 15:43
Rob. Like many others, A/C is a bit of a mystery to me although I do understand some of the fundamentals so, thanks for the very comprehensive postings above. You
mention, in one of the above postings "receiver/drier"
every 2 or 3 years. Is this a "consumable" item in the a/c system and, is it special to the Townace or can "pattern" types be fitted into the system? I had my system re-gassesd a couple of years ago with R134 but, as far as I know, nothing else was fitted or replaced. I should like to get the system in shape for another possible hot summer.
- (#6944) John Davis, 27 Jan 04 16:17
I have some knowledge of air conditioning also, but have no idea what the receiver drier is or does, so if any body can explain I would appreciate it.
There are some Sealing agents that can be used by air conditioning specialists. Its an additive that is injected into the system that will react and plug leaks as they develop.
There is an explanation at; http://www.coolprofits.com/articles/aircondition/ac_sealants_p1.htm but its not a DIY job.
- (#6944) dave Bright, 28 Jan 04 04:30
The receiver drier can sometimes be referred to as a filter drier, it is exactly that, the refrigerant is passed through it after it exits the condenser. The drier is a small cylinder (on the Townie it is mounted on a huge bracket just in front of the nearside front wheel on the inside edge of the chassis rail) it's purpose is to dessicate the refrigerant as it passes through the silica gell that it contains. The receiver drier can hold around a teaspoon (yes that little) of water. The reason for having it there is many fold, water will corrode internal components of the a/c system, water will also cause the lubricating oil in the system to emulsify & can also accumulate around the control valves & freeze, rendering the system useless. It is absolutely imperative that the drier is changed every 2-3 years (depending on usage) and also when doing a retro fit to R134a, as it will be contaminated with R12 & will be old by definition anyway. Just like changing your engine oil filter it is a preventative maintenance job.
HTH Rob.
- (#6944) Rob Drinkwater, 28 Jan 04 16:03
Thanks for your response Rob. Reassured that its OK.
Chris
- (#6944) chris turner, 28 Jan 04 16:11
Thank you Rob. Now I understand the importance of changing it.
- (#6944) dave Bright, 29 Jan 04 01:41
My thanks also Rob but, if you have time to reply, are these items available (like filters) or, are we in the hands of the A/C specialists re their supply?
- (#6944) John Davis, 29 Jan 04 04:15
As usual, the part is readily available, but the reference to them is not. I have a source of these if anyone is struggling, cost of around £40 if I remember correctly, this may be much cheaper than you average a/c specialist will charge you for the receiver drier. Please e-mail me if you need one & I'll try to get one to you & arrange payment.
Regards Rob.
- (#6944) Rob Drinkwater, 29 Jan 04 15:43
Thanks for that helpful advice Rob and, perhaps, when I get around to that part (A/C) of my pre summer preparations, I could contact you.
- (#6944) John Davis, 30 Jan 04 02:05