Rv2 A/c cool, not cold, but suction line gets cold

[WH23G3G]

So another issue with my 73 Charger 400 is the a/c is cool but not icy cold and dry like it should be. It's all brand new parts, rv2 compressor and new clutch. All hoses, evap, condenser, drier, valve are new. I put 10 ounces of PAG oil because it was a totally new system not an old conversion. I think we charged it with 3 cans of freon. The line on the back of the compressor sweats and gets nice and cold, and back to the evaporator it gets cool but not as cold as off the back of the compressor. The liquid line going to the drier isn't hot. After you shut the car off and the a/c off you can hear a squeal from the EPR valve inside the compressor. Is that normal? I know Classic Auto Air says you are suppose to remove that totally and run an electric thermostat but then I've heard some here that use the original system and it works fine. It would definitely be much more pleasant to drive with ice cold air because it's a pretty good running car now besides the driveshaft and the a/c.

[Pete in NH]

Hi,

First thing to consider- is the heater control valve fully closed? You have to make sure there is no hot water flow in the heater core.

On the A/C side of things, do you have a gauge set? Pressure readings would be helpful. Also, tests should be made at 1500 RPM engine speed, idle speed results with R-134A may not be that good. My 71 shop manual lists the system capacity as 52 OZ. of R-12. You want to start with 75% of this for R-134A or about 39 OZ. with 3 -12 OZ. cans you might be undercharged as you likely didn't get all 12 OZ in from each can.

The EPR valve regulates evaporator pressure somewhere around 26 to 28 pounds. You want that to be slightly lower at around 22 pounds for R-134A. Some EPR valves have an adjustment screw and can be reset, others are fixed. That is why Classic Air recommends removing the EPR valve and using a thermostatic switch. This will give you maximum efficiency.

Without pressure readings there is really no way to see what is going on and you're kind of flying blind. Also, what vent temperatures are you getting?

[WH23G3G]

Yeah I wasn't paying too much attention to pressure readings because the mechanic was doing it. But I know the low was high around 90psi and I think high side was in the 200psi range but not sure exactly. I just noticed the low was high. The pipe on the back of per was colder than before it reached the evaporator. I would guess temp out vents was high 60s-70s but didn't have a thermometer on it. I've got a factory 73 manual and it's not that much freon it's 38 or 39 ounces. I was thinking that rot was freezing up. How hard is it to install the thermostatic switch?

[Dino]

It's very easy to install that switch and very necessary!  The EPR valve is no longer needed.  When you top off the system with more freon, put the can in a bath of warm water.  It'll help to get all of the freon into the system.

It doesn't sound like there's anything else going on really.  Swap the EPR for a thermostatic switch, check pressure, and top off as needed, fire it up and go enjoy.  I loooove my a/c.   

[A383Wing]

did you pull a vacuum on the system for about 30 minutes before you put the 3 cans in?

[WH23G3G]

It may have been in the 20 minutes range. It was a totally dry system to begin with, everything was new, and never run. I looked on the classic auto air website for what they call a thermostat but I couldn't find the one they offer. Maybe it was someone else who offered it. Where can I get one? What does it take to install it? Do I just totally remove the epr valve and leave the suction screen intact?

[Pete in NH]

Look on EBay and do a search on A/C thermostat switch I saw many types available. If you get an adjustable type you can dial in the best trip temperature. You'll need to remove the EPR valve if there is one in the compressor, don't throw it away, those things are getting very pricey, if you can find them. Ideally you want to insert the sensing tube on the switch into the evaporator core fins and then you wire the switch is series with the power to the compressor clutch. This was the set up used on A body cars which didn't use an EPR valve until the mid 70's.

If you do indeed have 90 pounds on the low side that is way high something is not right. Like I said, you really need to get accurate pressure readings to know what is going on. Gauge sets are fairly inexpensive and a must have for A/C work. I don't know where your reman. compressor came from but, it's getting hard to find properly rebuilt RV-2's. I'd find out what the systems pressures are and go from there. If the suction side is really 90 pounds, I would fix that issue first. If your mechanic saw that 90 pounds and just returned the car to you with a very poorly working system, I would question his ability and knowledge about A/C systems.

[WH23G3G]

Is there a certain thermostat switch I need to get when looking on EBAY?

[Pete in NH]

Some thing with at least a one foot capillary sensing tube and an adjustable type that can be set in the 30 to 40 degree range would be fine. I'm sure you'll find many of these types listed.

[GMP440]

  Since you have vacuumed the system , your good there. 
I prefer to vacuum for at least an hour or two and then close everything off keeping the guages hooked up, letting the system sit for about an hour to see if there are any pressure drops.  If you have a drop , you have a leak.  Most common areas for leaks are at the shrader valves.
  As stated in the previous post get the a/c pressure switch mounted in.  Yes it can be dialed in to trip at either a lower pressure or higher pressure.
You need to know what the ambient outside temperature is to determine the proper low and high pressures.
There are R-12 and R-134 temperature to pressure charts on the internet.
Did the receiver drier feel very cold or or warm?  If warm you may have a restriction in the system.
Could be an issue with expansion valve or epr valve.  Both would show a high head pressure.  However 200 is not that terrible. but its still goes back to what your outside temp is.  A hot day like Florida would give high pressures and freezing temps would give very low pressures.

[WH23G3G]

Ok I'm trying this one more time. My freon must have leaked out probably due to the oil fill plug not sealing on the RV2 compressor. At least my low pressure switch is working right because it wouldn't turn the compressor on. So I want to re-vacuum down the system this time for an hour. Last time I did the recommended 15 minutes that came with my vauum pump and I don't think it was enough. So I definitely lost some oil since it was leaking out the oil fill plug before when the a/c was somewhat working. So I put in about 2 more ounces now. I'm going to try it one more time the factory way. Should I take out the epr valve and adjust it? I have the adjustable one I think. The factory tag says total charge of R-12 is 2lbs 14oz. So that's 46oz total. Would 3 12oz cans be about right for a recharge? Will an hour be enough to vacuum down?

[Dino]

An hour is plenty, but you need to leave the system alone for quite a while after you shut the vacuum pump off to enure it holds a vacuum.  Some people leave it like that overnight, I think I let it sit for a few hours while I ran some errands.  3 cans sounds about right.  I can't help you with the epr valve though, I'm running R134a.

[Bronzedodge]

Do you know anyone in the residential/commercial HVAC trade?  We pressure test with nitrogen.  Most good techs will have a nitrogen bottle and regulator on their truck.  The nitrogen is moisture free; aside from being able to leak test with soapy water in a spray bottle, it will displace any moisture in the system.   

[Pete in NH]

Since all the R-134A leaked out you will want to be sure you have found and fixed the leak. As suggested nitrogen is a great way to pressurize the system and do that if you have access to nitrogen. The RV-2 oil fill plug is a tapered thread type and originally had a bit of sealer on it. Make sure you have the right type of plug. You can check the oil level in an RV-2 with a simple dip stick. The factory service manual gives details on making one, I made one many years ago. It beats guessing about the oil level.

On the EPR valve, if you do have an adjustable type it will have a small set screw and lock nut in the center. Unless you make up a bench air pressure type test jig you would have to adjust it in the system. That is a huge pain to do as  you have to measure the suction pressure, recover the R-134A, remove the EPR valve, adjust it, put everything back together and recharge the system. You do this until you get the 22 pounds you want on the suction side. That's why it's easier to pull the EPR valve out and use an adjustable external thermostat switch.

Pulling a vacuum for an hour is okay, the longer the better to get moisture out. I do an hour to two hours close off the valve set paddle wheels and let it sit over night.

Make sure you've really fixed the leak, $45 worth of R-134A at a time can get expensive quick! 

[elacruze]

Yeah I wasn't paying too much attention to pressure readings because the mechanic was doing it. But I know the low was high around 90psi and I think high side was in the 200psi range but not sure exactly. I just noticed the low was high. The pipe on the back of per was colder than before it reached the evaporator. I would guess temp out vents was high 60s-70s but didn't have a thermometer on it. I've got a factory 73 manual and it's not that much freon it's 38 or 39 ounces. I was thinking that rot was freezing up. How hard is it to install the thermostatic switch?

As a rule of thumb, low side pressure correlates to evaporator temperature. 90psi on the low side says you have air in the system, supported by the fact that you know you had a leak. You were pulling air into the system while vacuuming. As previously stated, vacuum the system and let it stand for no less than 15 minutes, and you should lose no detectable vacuum. Add UV dye if your oil doesn't already have it to make any leaks easier to find.

[WH23G3G]

What kind of sealer needs to be used on the oil plug threads on the compressor? I've got a spare rv2 and another epr valve if I need it. How hard is it to wire in one of the thermostat switches? I saw some on eBay for around $10 and it looks like a 2 pin connector.

[A383Wing]

the oil plugs are pipe thread if I remember....Teflon tape could be used, but nothing was used from the factory

[Dino]

What kind of sealer needs to be used on the oil plug threads on the compressor? I've got a spare rv2 and another epr valve if I need it. How hard is it to wire in one of the thermostat switches? I saw some on eBay for around $10 and it looks like a 2 pin connector.

I got an adjustable thermoastat switch off ebay, it's not mandatory but the price was right so why not.  The wire running from bulkhead connector to compressor (blue I think) just gets cut and the switch is placed inbetween, that's it.  Don't use the epr valve.

For a thread sealant look up Nylog, it's liquid and works great.  I used it on all connections and green o-rings.

[Pete in NH]

What kind of sealer needs to be used on the oil plug threads on the compressor? I've got a spare rv2 and another epr valve if I need it. How hard is it to wire in one of the thermostat switches? I saw some on eBay for around $10 and it looks like a 2 pin connector.

I got an adjustable thermoastat switch off ebay, it's not mandatory but the price was right so why not.  The wire running from bulkhead connector to compressor (blue I think) just gets cut and the switch is placed inbetween, that's it.  Don't use the epr valve.

For a thread sealant look up Nylog, it's liquid and works great.  I used it on all connections and green o-rings.

There wasn't any sealer on the plug originally but since you think its been leaking making sure it is clean of any oil film and a little Nylog wouldn't hurt.

With R-134A I would pull the EPR valve out and just use an adjustable thermostat switch. It's the easiest way to go and allows you to dial in the best performance.

[WH23G3G]

Well I'm going to try one more time the oem way with the epr valve still installed. I believe the problem was with not vacuuming long enough before. I believe it was 10 mins or less. Plus the oil fill plug was slowly leaking. I've cleaned the plug and reinstalled it tight. Now tonight I've vacuumed it down for 1 hour and 1 minute exactly and now letting it sit for the rest of the night. It won't be until maybe Saturday evening or Sunday before I can try and add freon because I'm out. If all goes well and no vacuum loss over night will it be ok to just add in freon on Sunday or the next day I can get to it. Or will I need to re-vacuum it? I thought I had freon but I was out so I vacuumed it down anyway. Do I just leave everything plugged in tonight and just turn off the vacuum pump? Then just see if the needle has moved over night?

[A383Wing]

yea, pull vacuum, turn pump off, and see if it stays the same overnight

[Pete in NH]

In all your postings I'm not sure you have ever mentioned using a gauge set. You are using a gauge set while pulling a vacuum right? After letting the vacuum pump run for a least an hour close off both side valves on the gauge set and let it sit overnight. You will also add you new R-134A through the suction side gauge port, after purging the air out of the hoses on the suction side. While charging the system the discharge or pressure side valve on the gauge set remains closed.

[WH23G3G]

I let it sit hooked up overnight after getting done vacuuming and checked it this morning. There was no drop of the needle on either side. I'm going to try and recharge this weekend.