95 p30 chassis location of air conditioner system orifice tube

[jimntempe]

Hello,

Just got a 95 Winnebago built on a Chevy P30 chassis.  Owner said he believed the AC needed a new orifice tube and recharge.
  I recharged the AC and it's working but pressures are a bit high, high enough that it could have some restriction in the orifice tube so I'll like to put a new one in.. but can't find out where it's located!!
Does anyone know the location of the orifice tube on this thing?

 

[Gary RV_Wizard]

Not an a/c guru, so didn't know what an "orifice tube" is. Had to look that one up!  However, it's a standard automotive system, probably from Evans Tempcon, so the components ought to be readily identifiable.  If it is an Evans system, it could be integrated with the heater/evaporator assembly?  I dunno...

Maybe some help here:  http://www.evanstempcon.com/troubleshooting.php

Orifice tube:  https://technician.academy/what-does-an-orifice-tube-do-in-an-ac-system/

 

[jimntempe]

Thanks for the comments.  From what I see the vehicle just has a factor GM AC system on it, at least all the parts under the hood are standard GM AC and Heater parts.  The dash is winnebago's cross panel but all the stuff in the dash is standard gm instruments, controls and switches other then the control panel for the hydraulic jacks.  I assume they simply add their own dash vents to the GM ac/heater box.

 

[Heli_av8tor]

The orifice tube (if it has one) has to be close to the inlet side of the evaporator coil.

Many A/C systems (such as mine) use an expansion valve instead. It is also going to be located right at the inlet to the evap coil. Mine is in the same housing.

Tom

 

[jimntempe]

Yes, I did see what appears to be an expansion tube "block" at the evap inlet.  Looking online for parts it seems there is also a listing for an orifice tube. So some confusion as to whether it has one or both of them in there somehow and if so where.  Hate to take the block off if there's no o tube hiding behind it.
Thanks for the feedback.

 

[rls7201]

If you have an orifice tube you will have an accumulator tank in the suction line close to the fire wall. If you have an expansion valve you will have a receiver/dryer just down stream from the condenser.
Orifice tube systems flood the evaporator and require an accumulator tank to keep from slugging the compressor.
Expansion valve systems require a receiver/dryer to make sure the expansion valve gets 100% liquid refrigerant.

 

[jimntempe]

Thanks.  I'll take a second look.  WHen I was in there I did not see an accumulator like most light cars have but did see a receiver drier next to the condenser.  Based on your comments it sounds like the most likely case is that it just has the block expansion valve that's just before things go into the evap case.  Any idea if those block exp valves can get blocked like orifice tubes do over time?  All things considered it doesn't look too hard to replace assuming the fittings aren't stuck. 

 

[Gary RV_Wizard]

Looks like the Chevy P chassis did come with much of the a/c stuff installed. (The Ford chassis did not)

I looked at a 1990's vintage P30+G30 chassis manual and it says this about the factory a/c system. It includes info on both the G series and P series, so read carefully. Note that it says a "thermostaic expansion valve" for the P-seres chassis.

System components include a compressor, condenser, expansion tube (G-Series) or a thermostatic expansion valve
(P-Series), evaporator, and an accumulator or a receiverdehydrator.  In operation, the compressor produces the
pressure which moves refrigerant through the system . Liquid refrigerant passing through the restriction of the expansion
tube or valve changes into a vapor as it enters the low-pressure environment of the evaporator.

Download the manual at https://www.gmcmi.com/wp-content/uploads/2014/05/P30-Chassis-Manual.pdf

 

[rls7201]

Thanks.  I'll take a second look.  WHen I was in there I did not see an accumulator like most light cars have but did see a receiver drier next to the condenser.  Based on your comments it sounds like the most likely case is that it just has the block expansion valve that's just before things go into the evap case.  Any idea if those block exp valves can get blocked like orifice tubes do over time?  All things considered it doesn't look too hard to replace assuming the fittings aren't stuck.

That block exp. valve is definitely aftermarket. GM did not use a block exp. valve back then. They have always been problematic. I can't even begin to guess at how many I've change in my life time, especially on MOPARs. It's probably not blocked but failed. If you elect to change the exp. valve, make sure and change the receiver/dryer too. And blow or flush out the line between the two devices. Then don't make the rookie mistake of not drawing a vacuum on the system for at least 30 minutes, before charging. In order to get all the moisture out of the pores of the system, it takes at least 30 minutes. The liquid in the pores boils off and is then pulled out as a gas. This creates a cycle in the vacuum that must be maintained until all the moisture is out.

As per the previous provided manual, page 2-2.
The P-Series system is installed by the body manufacturer.

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