HVAC gurus - How do I test an auto AC expansion valve

Based on your infomation of vehicle year, make and model this system uses a "Fixed Orriface" an not an expansion valve. this early system was R12 freon and when converted to R134 caused the problem you discribed. later on we found that R134 was not compatable, later a new type of orriface was released but still not efficent. most of the time going back to R12 was the only cure. Ken Humphreys AEE, AME, ASE Master, Educator.

Thanks for a reply Ken. This is an aftermarket AC system (SGS Frigette) R134a installed by a auto AC shop, not a shade tree shop or homeowner. And it was working fine for years and years. It is MOST definitely an expansion valve system with no orifice tube. Eaton expansion valve, single acting (one capillary coil). The entire system is disassembled and blown out with $100/gallon AC flush and not one spec of black death was found, and no contaminants or particulates of any type. I don't have a diagram of the heating system and the Haynes books don't show it well to see if this is a combo AC heating system where the heater core can fight with the AC if that system isn't operating right. I poke my head under the dash. Internet search for the heating system diagram didn't produce much.

Sorry, did not know it was an aftermarket unit. The best bet is to find and replace valve. This situation, installing A/C on Vehicles dilivered with no A/C, is always A problem with no info on installed package. Can't help much with out hands on check out. Thanks for your reply. Ken

Hi Ken,

I reassembled everything this weekend with a new valve found in a picture book of Eaton valves. Pulled vacuum for 3 hours but after 5 minutes the vacuum didn't change any. Filled and tested with 35 psig on the low side, 250 +/- on the high side with 95*F ambient, but still no improvement. Duct temps are still about 65-70* F. Even though the condenser blew out clean and free of major restrictions, I'm now noticing the condenser has little temperature drop. The temperature coming into the dryer is about 160*F guessing as I can't hold on to the pipe and my fingers are normally good for 145*F or so. I can feel a slight chill, nothing to write home about, after the expansion valve on the inlet to the evaporator. By temp difference it is a huge drop, maybe 100*F, but still not freezing cold as I'd expect it downstream of the valve. Not too many web sites with trouble shooting tips. Now checking into my fan clutch.

Hi, This is Ken again. Try running garden hose accross Condenser while checking Temp at ducts, hope you are using a non contact infared gun, if a large temp drop is noticed, air flow is restricted accross condenser. Also if temp is lower on outlet side of reciever/drier, any restriction in drier will act like an orriface and reduce the ability of expansion in the evaporator. Also make sure to find the exact freon requirement is what is in the system, R134 is NOT as forgiveing as R12, 4 Ounces over or under and system is not sufficent for high ambiant inviroment. Good Luck,Ken

Good ideas Ken. I tried shop air last night to supplement the fan (fast and easy), but I don't have a IR gun yet (on the list). No noticeable drop in temp with shop air. I'll wheel it out of the garage today for water test. I did a water test on my home condenser when is 1 meter from my garden hose to see the delta T air temp and it made a heckuva difference so I suppose it will open my eyes on the car. The condenser blew out free but did develop about a 10 psig back pressure (guessing) with about 50 psig going in (guessing again) with the AC hose still connected all the way to the dryer inlet (but disconnected from the dryer inlet and all liquid blown out, so back pressure was air to air, not against a slug trapped somewhere). I've never blown out a new one to see if they are restrictive generally due to small pipes and many turns plus the hose diameter and the 90* bend of hose fitting tubing termination; looks like 1/2 tubing size.

By feel of hand, the dryer feels the same temp in as out. I'll get an instrument today. The volume of 123a is only a guess as the system is aftermarket. I'll try to call the supplier. I burped in liquid in small steps to check performance, then let out some gas to back check performance and it wasn't so sensitive. Started at 20 psig and went in 3 psig steps to 40 psig. No real changes. Just by chance, do you happen to know if the heater circuit is in constant fight with the AC meaning the heater core is flowing 100% but not ducted in, or, is there a manual water valve hiding under the dash? There is no heater circuit valve in the engine compartment making me think the heater core is constant flow and the Hot / cold lever throttles a blend door ? I'm too fat and the (quad focals don't help) to hang upside down under the dash. I notice a slight movement of the cold <> hot lever (1/2 ") brings warm air in.

Hi Petro, Ken here, To elliminate a possable problem with Blend door and injection of heat just clamp off heater hose in engine compartment. let me know when you can get water over that condenser. there should be no restriction through condenser, look to see weather its a single pass, one tube in and out or a collector type. that type has a tank at each end. when you get the IR temp unit make a pass over the condenser and watch the temp. you may have a cold spot. IE blocked passage. Ken

Hi Ken,

Remember me? Well, I reached the manufacturer of the system, SCS Frigette in Ft. Worth and they told me the exact quantity of R134a (26 oz) and PAB 100 (8 liquid oz) so I vacuumed it down to -15 " Hg and let it sit for 2-3 hours and then reintroduced the exact quantities (drained all oil, etc). Exact weight of R134a with a very accurate scale.

Remember, there were no blockages that I can tell by blowing air through the evaporator, hoses, condenser (a tiny bit of restricting) . There are 14 end turns in the condenser and 5-6 gangs of collected tubes on the hose side. 3/8" tubes.

Still no change; 60* F duct air still, 85-90*F ambient, inside / outside air door is closing (audible) and pinching off heater hoses has no effect, switching off compressor raises duct air temp to 75* or so, therefore I don't think outside air is coming in nor is the 'constant on' heater core blending hot air to my cold air. Air flow good through radiator, shop air blowing through radiator to help fan (in case fan clutch kind-of bad) also has no effect, RPM 1500 during tests.

I now have a thermal gun and the condenser is 158*F at top and 155* mid point +/- and 152* F at bottom so for me not much delta T. Compressor discharge about 165* F, inlet to dryer and dryer 168*F, significant drop across expansion valve but I can't get my gun down there . . . just feeling with my finger tip it feels like this 168*F dryer temp down to 35-40* F or so; dew drops can be seen. Might be cooler (I'd guess it should be a lot more drop, but that 168* F dryer temp worries me. There is no delta T across the dryer so I guess it is unblocked (it blew through fine by mouth) and I 'boiled' all the moisture out at -15" Hg real good.

Spraying the condenser with water dropped the duct temp to 45*F.

Low pressure 30-33 psig, high at 270-290 psig depending on ambient. High went down to 220* psig by water spraying condenser.

Good air flow out ducts and movement of 3/4 " on the cold <> hot lever starts blending hot air right away.

I replaced the expansion valve but didn't get the exact same Eaton part number. They look absolutely identical in every way except the part number.

An AC pal who is out of ideas (by phone) told me expansion valves don't work on R134a. All R134a are orifice tubes. This was installed as R134a from the get go although I'm the second owner. may have been converted from R-12 but SCS Frigette was not concerned about exp valves and R134a.

What gives?

Thanks in advance.

Hi Petro, Well one thing to note is that -15 in is now were neer what is needed a true A/C evac tool goes to -28 in at ambiant temp of at least 80 deg. Also note that many Car Manuf. do still use TXV's with very goog results, the orriface is smaller for R134 but 45 deg of duct temp is well with-in design, probably not enough air is going through condenser. Engine fan may be problem, could have been ok for mid summer heat load in northern climbs, not in south like Florida. If you have a clutch fan it may be bad, if spacing to radiator is too wide or air is going around sides of condenser. Also don't allow outside air to go through evaporator. try operating in "MAX Mode" and take it on higher speed road for 10 to 15 miles and see if it will then cool the interior of car. Ken

I suspected my -15 is wimpy but it's all I can get from this 30 YO vacuum pump I borrowed. This is one of those older basket ball refrigerator type pumps, not sure what's inside but I guess a rotary ?? are the seals might be kaput (or bands and valves if a piston). I'd like to see -25 and called around and no HVAC guys I run around with had a comment on this. They thought -15 was OK . . but, my pals are good-old-boy AC guys, not science guys. I guess I should buy a new 'real' vacuum pump from ?? Master Cool or Robinaire? I like to get a proper one to service my other 3 cars someday. 25 micron 5 cfm ?

Just about everything I read says you cannot dry out a dryer once it's opened up even with 0 micron as the oil prevents silica gel boiling out all the water. Not sure if I understand this.

The fan shroud is missing also and I suppose that is a huge issue with fan performance. I've never known if the AC was really working as others have been driving this car, but they say it was 'fine'. What is fine? I'm also at 5000 feet alt so that doesn't help either.

I did take it for a fast drive but didn't notice any changes with duct temps. Plus the shop air augmenting fan flow experiment I don't think was a fair comparison to ram air at 30 MPH + as it is too localised. So, my last ditch ideas are to buy the proper expansion valve new now that I have a source, just in case the orifice size is different, find a fan shroud in a wrecking yard, and try a new fan clutch (which is a good idea every 10 years or so anyway living in the desert as I do). Then I'll measure the condenser delta T on 3 other cars I own and restrict air flow and see if I can duplicate the Bronco II deal.

I remember another friends car fan that I thought was flowing just fine based on the blast air coming off the back, but, then darn car still overheated, so I suspected the fan clutch due to radiator water delta T . . . . so I 'locked' up the clutch with hot melt glue before removing it as an experiment and it sounded like a jet engine ! Fan flow is 1:1 ratio with speed.