AC Expansion Valve

[Sam280Z]

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

[z240]

There is very experienced Datsun A/C guy over on classiczcars.com. Search for user sblake01. He may be able to help.

 

Jim

[Pyro]

buy a new z evaporator core that takes a standard style expansion valve that works better with 134.

[Sam280Z]

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 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.

[greghassen]

Did you test your ev by putting it in a freezer?

 

You can charge it with another refrigerant thats r12 compatible like envirosafe until you get the pressures

fixed. I would set the superheat screw in as far as the others you have. All the expansion valves i have are screwed

in about the same distance.

 

After you get everything sorted, I would highly recommend a flushing with solvent

of the whole system, replacement of the dryer and filling with the proper amount of refrigerant oil.

 

You can use lacquer thinner or brake cleaner and an air compressor to flush.

 

The reasons for a proper flush are:

1. You need to get the correct amount of oil in there and after charging and discharging. Lots of oil escapes with the gas.

 

2. Doing that much work can dislodge sludge in system.

 

 

Are you evacuating the system before charging? if not i wouldn't recharge with the

r12

Edited August 21, 2010 by greghassen