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Topic: Rebuild 1991 GV GAST 5HCD-10-M500X Onboard air compressor (Read 693 times) previous topic - next topic

Rebuild 1991 GV GAST 5HCD-10-M500X Onboard air compressor

Finally got time to rebuild the GAST onboard air compressor. Searched this forum, I couldn't find any post regarding the rebuild of the air compressor.

The rebuild kit number is K-263

I bought from GPIndustry USA, They seems to have the best price.

There is no video on youtube match the exact model no. I found this one is almost identical to the aux compressor on 1991 GV
https://www.youtube.com/watch?v=T2HDVXFskEY

Other than few seized bolts, the process are relatively easy. The old gasket are definitely worn out turns into little pieces.

After rebuild the air compressor, it does run smoother, less vibration. I added this to the outlet of the compressor, then a check valve then a T fitting. One side of the T fitting go to the pressure switch, Pressure switch set at 100PSI. The other side of the T fitting connected to a quick air fitting. Just in case I need air for some other use.  With this setup, the air filter will remove small particles and water form air. When air pressure reaches 100PSI, air compressor stops. Check valve hold the pressure. No pressure on the air filter. The accumulated water will then be disposed.

When the compressor runs, it draw about 12 amps. My storage place only have 15 amp plugin, so it tripped the breaker few times if other electronic run at the same time.

I initially though the air compressor is going to be air tight. But regardless how hard I tight the bolt, there is still air leak. Then I realize that why a check valve is on the air schematic. With check valve, the compressor does not need to hold pressure. It only needs to build pressure then it is isolated from the rest of the air system by the check valve. I spend so much money on different kind of air fittings but what I really need is just a check valve. I guess that is the price I pay to learn the air system.

I tested the aux compressor with a portable tank. It can hold pressure for days. So the check valve and fittings are good. But once installed on the GV, there are significant leak some where. Air pressure drop from 90 PSI to 0 in less than hour. That is some significant leaking. I could only find one air leak at one of the front air bag by using soap water. I couldn't hear any sound of the air leak. This is really annoying. Searched on this forum, I guess I have to live with that. I wish it could leak less so that I can use the manual leveling system.

Probably it doesn't make any sense financially to rebuild the compressor. The cost of the rebuild kit is about the same as some new portable air compressor and the amount of air fittings I bought is really concerning :'( . Working on 30 year old coach will never make sense from financial perspective.

BTW: Do we have air schematic for 1991 GV with manual leveling (without HWH) on this forum? I couldn't find one. Thanks in advance.

1991 Grand Villa U300

Re: Rebuild 1991 GV GAST 5HCD-10-M500X Onboard air compressor

Reply #1 –
Here is photo of air schematic and legend for 91gv

Ken
Ken & Peggy
91 GV  U300 40'
DD 6v92
Build #3819
2023 Canyon Denali 4x4 crew cab

Re: Rebuild 1991 GV GAST 5HCD-10-M500X Onboard air compressor

Reply #2 –
Running, sent you a message
Rudy Legett
2003 U320 4010 ISM 450 hp
2001 U320 4220 ISM 450 hp
1995 U320 M11 400 hp
1990 Granvilla 300 hp 3208T
Aqua Hot Service Houston and Southeast Texas

Re: Rebuild 1991 GV GAST 5HCD-10-M500X Onboard air compressor

Reply #3 –
Quote from: kpbowser –
Here is photo of air schematic and legend for 91gv

Ken
Thanks for sharing the air schematic.
On the drawing

V is probably the air bag

I also see X and W

They are not listed on the part list.

What would be the part number for these two?

How do I convert the Foretravel part number like 700053 to manufacture part number?
1991 Grand Villa U300

Re: Rebuild 1991 GV GAST 5HCD-10-M500X Onboard air compressor

Reply #4 –
V = s
W = t
X = u
I never have been able to cross reference there part number to useful info. Use the search option and put in the parts name and you will find all kinds of info.

Ken
Ken & Peggy
91 GV  U300 40'
DD 6v92
Build #3819
2023 Canyon Denali 4x4 crew cab

Re: Rebuild 1991 GV GAST 5HCD-10-M500X Onboard air compressor

Reply #5 –
Follow this post Likely air leak locations

Just did a test, after the air pressure reached 90 PSI, turned off the aux compressor.

Open the wet tank drain plug, air pressure gauge show both tank air pressure drops.

Turn off the wet tank drain plug, open the front tank drain plug, air pressure drops for both tank.

It seems like those check valves are not working. They are not leaking air verified by using soap water. But they are not stopping air from flowing the other direction.

Open wet tank and pressure drops, that mean the check valves to either front or rear tank is not working.
Since both air tank pressure drops when open one drain valve, that means the double check valve is not working.
According to schematic, the only connection between two tanks are the double check valve (K)


Time to read @Chuck & Jeannie  great post Air Tank Valves R&R

Check valve part number is Bendix 227871 SC-1, will start from this simple step. After change this two check valve, the air pressure gauge should not drop when wet tank drain plug is open.

1991 Grand Villa U300