Need some more help from the AC gurus on here

[tbrumm]

I am going to be taking my truck in soon to have the AC system evac'd, leak checked, recharged etc. by a local shop. I don't think I have any leaks as the system is holding pressure and does cool somewhat. This is a dealer installed AC system with an expansion valve. It has a newer parallel flow condenser, the Seltec compressor seems to run okay and is quiet, I have cleaned out the evaporator and that seems to be fine. The problem I continue to have is the low side pressure is still too low (20-25) and the evaporator seems to be freezing up blocking the system. The thermostatic switch does kick out the compressor when the system freezes up but then it takes quite a while for the evap to thaw and to engage the clutch again. Anyway, I want to purchase a new receiver/dryer and take that along and have the shop install that when they evac the system. Unfortunately, I can't find any part number or markings on the dryer to tell me which one to get. I have attached a couple of pictures so I am hoping you ac gurus can tell me what kind of fittings are on the dryer. It obviously has a binary switch on it too. Any suggestions on where to order it form? Thanks very much for your help! Todd

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[typ4]

I bet those are -6 flare fittings and I think Napa has that dryer in their picture book. 208301 in temp products
If it is insert o-ring style they have many that will work..

 

[icanfixall]

Russ is probably correct but I'm going with the o ring type fittings. The 25 lbs on the low side should not be freexing up the system at all.

 

[chris142]

its just a universal dryer.

 

[typ4]

Blew up the picture it does look like the oring insert. if so might be this one napa TEM 208486

It sounds like the thermostat is not shutting off the compressor and the low side switch is after it freezes up the evap. Could have dirty fins also, cant transfer the cool off the fins.

My best experienced guess, also if it cools well enough to freeze down, you dont need a dryer.

 

[FordGuy100]

Check to see how dirty your evaporator is. What are the high side pressures and ambient temps?

 

[tbrumm]

Thanks for the replies, guys. I am only getting marginally cool air in the cab and all the components seem to be working so I was thinking I had moisture in the system freezing it up. The lowest temp I can get in the center duct of the dash is 65° with ambient outside temp of 80°. The evap is clean - opened up the plenum and vacuumed out a few bits of leaves and pine needles, but fins are clean and drain hole is open. While I am getting 20-25lbs on the low side, the high side is up around 200 at 80° ambient temp. If I try adding more R143a to bump the low side, the high side really starts to rise. Not sure what else to check here. I appreciate any more suggestions you guys might have.

 

[typ4]

So its not icing up the fins? Thats different, sounds like possible expansion valve, and yes if it freezes from system moisture it will make those pressures.

 

[chris142]

200psi@80f is overcharged or not enough air through the condenser. you could have hot water heating up the ac too.

 

[tbrumm]

Russ - yeah it isn't the fins in the evap freezing - I think the system is freezing up internally and causing a blockage. The expansion valve is for R134a and was new a couple of years ago. I also have the exp. valve insulated from engine bay heat.

Chris- I have a heater shut-off valve installed that shuts off water to the heater core when the system is set to MAX-AC. If I "reduce" the charge in the system, I basically stop getting any cool air at all.

 

[tbrumm]

It was about 85° here today and I ran the AC on the way home from work. Center duct temp got down only to 75°. After running down the highway for about 10 minutes though, it suddenly started blowing nice and cold - that lasted about 30 seconds and it was back to only slightly cool air.

 

[tbiagent69]

Was the system evacuated when you pressurized it last time? Expansion valves are a lot more sensitive than orifice tubes when contamination is in the system.

Where is the temperature sensing bulb for the expansion valve located? If it is not connected it is possible that it is not regulating properly.

With the system running, what does the window on the top of that receiver/dryer look like?

I'd say to evacuate the system, pull vacuum on it and recharge it.

I used to use the manifold gauge system from Autozone, but I bought the one from harbor freight yesterday and was surprised to see that it has vacuum as well as pressure, so pretty cool..

If you don't have any of the tools you could get the vacuum pump and the manifold set for about $130 and they're well worth it in my opinion.

 

[tbrumm]

tbiagent69 - thanks for your reply. I have a good gauge set, but no vac pump or recovery gear. I can't see the sight glass on top of the dryer because of the mounting position. The exp valve does not have a tube with a sensing bulb attached to itI think I am just going to take the truck in and have the system evac'd and recharged. A dryer is not all that expensive either so I am going to have a new one installed too. Maybe a new expansion valve would be a good idea too.

 

[tbiagent69]

Sounds good. I've never taken my AC in to be serviced before, but I've been told that they will not recover contaminated freon so you may be in a tough spot. I know it seems scary to work on it yourself, but as long as you don't give yourself frostbite or inhale the vapors you should be ok.

 

[Shadetreemechanic]

If you are having the system evaced and replacing the dryer, go ahead and do the expansion valve. That is the cheapest opportunity you will have and a bad expansion valve will cause those symptoms.