Low Side Frost - Finding the Problem.

[Z2TT]

Hi,

1987 Toyota Soarer, uses a Expansion Valve System.
The last time I had the system gassed, I had noticed a small layer of ice forming up on the low side coming out of the firewall for the first 10cm or so, very minute but noticable. I assume this isn't good as if the low side is freezing, liquid could enter the compressor and cause a failure, the compressor was failed when I bought the car, I have replaced it.

The Service tech also mentioned that the high side pressures were a bit too high.

I'd think it could be a Faulty TXV Flowing too much refrigerant into the evap, but my system uses an EPR valve, so could it be a faulty EPR Valve not restricting enough flow from the evap causing the low side to frost up?

As I don't have equipment to charge the car at home, next time I get someone to regas it, what things Should I take note of to be able to give me ideas of what could be causing the low side frosting.

The type of gas being used is a Hydrocarbon gas, Butane/Propane mix.

Thanks.

[monkey spanners]

Ice does not mean liquid, just means what ever is exiting the evaporator is below 0C, vapour can be below 0C also. Liquid can be above 0C so a lack of frost does not mean you can't have flood back....

Is the refrigerant you are using a propper replacement for R12? Because if it isn't you TXV isn't going to be able to regulate its flow propperly.
It would need to have the exact same pressuer temperature properties as the refrigerant it replaces for the TXV to work effectively.

[Will]

An '87 ?, dirty evap ?

[Z2TT]

Monkey Spanners, Here is the pressure temp chart for the refrigerant, it's called HR12

http://www.hychill.com.au/tech/ptc.htm

At 30C for example R12 is 93.5 PSI while HR12 (The hydrocarbon mix) is 104.2 PSI

Will do you mean an evaporator thats dirty with leaves/dirt etc? The evaporator was very clean when I had a look at it.

[Z2TT]

I have read an online quiz on A/C

http://www.tomorrowstechnician.com/Article/4979/tt_april_08_pop_quiz_ac_systems.aspx

There was a question about identifying a restriction in the system (Question 7), and if you look down at the answers, It says it can be identified by seeing ice forming at the restriction area. Would that mean I have a restriction where I see the frost forming?

[bruisermac]

frost on the suction line is normal. it should "sweat" a bit. most car evaps are flooded anyway.

[Z2TT]

Thanks, Seems on most cars it's common to see a bit of moisture/frost on the low side.

What do you mean when you say "Most car evaps are flooded anyway"

[bruisermac]

Since liquid and vapor are forming in the evaporator, the vapor volume leaving the evaporator tends to "drag" liquid out of the evaporator too. If operating properly this process occurs at the saturation temperature of the refrigerant for the pressure maintained in the evaporator by the compressor. There should be NO superheat!

The reason for why this type of heat exchanger might be selected is the higher capacity available for the same amount of heat transfer surface. If you use the heat exchange surface for superheating the vapor you are not evaporating liquid, hence you get slightly less cooling capacity.

this was quoted by "iceman" in another post and is a good explanation i think.