I'm trying to get AC going in my 78 280Z. I have everything installed and ready to go. I tried to buy a new expansion valve but they are NLA, so I am stuck using an old one. I have four and will use the best one and keep the others as spares.

One of them was pretty corroded. In cleaning it, I managed to take it part before realizing that the screw that holds the spring in also sets the superheat of the system. Now that it is apart and cleaned, is there a way to set the superheat back to specs? Every instruction I have found online indicates setting it with the expansion valve installed on a running system. This won't work on the early AC systems because the setting screw is inside the running system. I only want to do this once - R12 is not cheap.

My questions are:

How do you set the superheat?

Is there a way to test an expansion valve before installing it to be sure that it is working?

Thanks,

Sam

Due to the age of the expansion valves in question, I clean them with a flush. I would never dissassemble them because you won't find any instructions on how to set/adjust them when you reassemble them. I've looked and I've never been able to find any instructions to do such a setting on these old systems. My conclustion it that they were pretty much 'set at the factory' so to speak.

sblake01,

Thanks. This one was pretty shot. Don't know if a flush would have gotten the rust out, so I don't feel to bad if i've ruined it for good.

Is there a way to see if they are even operational before installing? I'd like to test my other ones.

I've found the following in reference to converting to other refrigerants at http://yarchive.net/ac/expansion_valve.html

"The superheat must be set. This is normally done by an adjustment

accessable through the outlet port of the valve. To set the superheat,

one needs a source of pressure, a gauge and a thermometer. Connect the

gauge and pressure source to the outlet port (flow backward.) Measure

the temperature of the capillary tube. Subtract 10 degrees from that

value. This is the superheat. Look that temperature up on the

refrigerant's vapor pressure table and note the PSI. Turn on the

pressure source regulated to a low flow and adjust the superheat screw

to achieve this pressure. For example, if the temperature is 70

degrees, subtract 10 to get 60. If the vapor pressure is 30 psi, set

the pressure to that value. (these are made-up numbers - consult the

vapor pressure table for your refrigerant of interest. Put the system

back together, charge it with the new refrigerant and enjoy."

Does this sound reasonable?

Sam

Edited August 11, 201014 yr by sam280z

I don't know of a way to test them before installing. That procedure sounds reasonable. I've never tried it, however.

Sam,

It would be far easier for you to install a new Evaporator and a modern Expansion Valve rather than try to clean/reuse a 32 year old EV. The effort alone is pretty substantial. If the EV is dirty, then that means that the Dryer or compressor has problems and has begun to throw off debris. In these old systems the refrigerant oil has almost certainly began to degrade and turn brown and get sticky - jacking up everything.

I would suggest that you flush the Compressor and Condenser; Replace the Dryer, Evaporator and Expansion Valve. (Make sure to add 9.5 oz of refrigerant oil - specifically for R12 into the Low side). Do not add Polyol Ester oil to an R12 system it will gel any residual Mineral Oil.

If you can afford it (and it is practical for you), It would best to replace the components and charge with R134.

I can help you either way - I have already replaced the AC in my 78 Coupe with an R134 system. I know where to get the parts, etc. I am also IMACA(MACS) certified.

Do what is practical for you. Let me know if I can help.

Good Luck,

Andrew, Thanks for the offer.

I have already flushed the whole system. I'd rather not remove the evaporator because I have an un-cracked dash and I don't want to risk cracking it with the removal. I have the system charged with R12 now and it is cooling marginally with high side pressure of 250psi and low side of 30psi. I foolishly just stuck the valve that was in the car back in with new O-rings after blowing through it with my mouth and comparing it to a brand new valve that belongs to a friend. I should have cleaned it out, but didn't.

I think it is partially clogged because the EV housing is sweating and the high side line gets pretty hot in the evap housing. By pretty hot, I mean it will burn you if you touch it too long or too hard. Does this sound right?

I'm not running the system without gauges though until I get all these issues sorted out. of course, I'm in Louisiana with 90% humidity and high 90's F. So the suffering continues.

When I charged the system, I had bypassed the pressure switch, thermostat, etc. and activated the clutch directly because the AC relay was missing. In hindsight, this was a mistake. Upon replacing the relay, I discovered the pressure switch was bad. So, I have to pull the system down again to change that anyway. I have an expansion valve that was pulled from a recently operating system - the compressor seized after ten years of use. I went through all these same issues getting it going back then - except the EV was completely plugged (took me a while to figure out why the suction side was pulling a vacuum no matter how much freon I put in). Back then you could still get new EVs so i just dropped a new one in.

Thanks,

Sam

Edited August 12, 201014 yr by sam280z

Sam,

I believe that you can remove the Evaporator without pulling the dash although it will be quite difficult. I can understand not wanting to mess with you dash though.

It sounds like it is fundamentally working, but it is plugged somewhere hence the 250:30 ratio. Generally it is a 10:1 and 250 on the highside is too high. I am betting that the EV has some crud in it. The Highside line is supposed to get pretty hot - not enough to burn you but pretty uncomfortable to touch. I live in Houston so I know what you are talking about with the heat and 100% humidity!

I would take the EV out and clean it with AC Flush (and leave it out). Take the Dryer out and throw it away. Flush the Compressor, the Condenser, Evaporator and the disconnected lines. You may need to Flush the Condenser and Evaporator twice.

Reassemble everything, using refrigerant oil (AC Mineral Oil for R12) on the o-rings, compression fittings - be generous with the oil. Use a new Dryer. Add the proper amount (I believe 9.5oz) of Refrigerant Oil to the low side.

Pull a vacuum to like (-25 to -30 atm) and let it sit for 30 mins. Check for leaks (Needle rising). If all is good and with the engine off, put one can of R12 in AS LIQUID (can held upside down) into the system. Start engine and top off with R12 (I believe that it is another can and a half).

If there are no leaks and it is clean - it should cool like a meat locker.

Good Luck

i need my AC worked on.. it works but the stuff that is inside it is oily brown crap and it hardly cools at all.. and im guessing it was converted to r134a because it has the fittings on it for r134a connections.. and it seems to have some of that in it right now.

should i simply go get it vacuumed out and refil with r134a?

Get the system inspected by an accredited shop. They can identify the type of refrigerant. If it has 'oily brown crap' in it chances are it needs other work. Having R134a type connections doesn't necessarily indicate that the system has R134a in it. I install those type fittings on any of the older systems I work on just because they are easier to use. Like Andrew, I'm also a licensed HVAC/MVAC tech. If your system was legally retrofitted, the should be a refrigerant tag somewhere under the hood.

ah i see. i havent seen a tag anywhere so i assume it wasnt. and i assume there was some r134a because thats what the guy said was in it when i bought it.. right now the whole system doesnt even kick on. no fans no nothing so i got to fix that first.

would you know how much it would cost to replace some of the parts like the expansion valve to newer 134a parts and do the conversion?

I've never been a proponent of putting R134a in a system that was designed for R12. The R134a molecule is smaller than the R12 molecule coupled with the fact that R134a requires higher pressure to adequately cool which would tend to make the system more susceptible to leaks than a system purpose built for R134a. For that reason I've always used either R12 or a R12 substitute like Johnsen's Freeze 12 when charging an R12 system. I know R12 costs a fortune these days but I lucked into a jug of it at a yard sale last year that had about 23 lbs. left in the cylinder and the lady sold it to me for $25! Systems become problematic for different reasons so I would only be guessing at the repair cost without actually doing an inspection.

Edited August 13, 201014 yr by sblake01

ah i see. no i agree with you, id rather have r12 in it then 134a. i had a bmw with r12 and that thing was a ice box. ive been in brand new cars in 110 degree weather and it was never as cold.

in that case i hope mine isnt r134a.. and since you said there would be a stamp i assume it wasnt, or the dude vacuumed it out and didnt put r12 back in. if that is the case could there be any damage to the system if not converted properly? or can i just flush it out and put r12 in it?