| Time delay on original roof AC's [message #301951] |
Fri, 10 June 2016 08:18  |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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When I purchased my coach in 2002, one of the many things that needed work were the two roof AC's. Both of the would run the fan, but neither would start and blow cold air. Someone mentioned the following modification which removes the time delay and allows the AC's to work.
http://www.gmcmhphotos.com/photos/g3615-roof-ac-modification.html
Someone receintly asked me if there was a down side to doing this modification. Is it ok running with out it? Anyone know?
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: Time delay on original roof AC's [message #301961 is a reply to message #301951] |
Fri, 10 June 2016 11:33  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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The reason for the delay is to give the high and low side a chance to equalize pressure like Matt says otherwise you could trip the breaker.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Time delay on original roof AC's [message #301963 is a reply to message #301956] |
Fri, 10 June 2016 11:49 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Matt Colie wrote on Fri, 10 June 2016 10:06Larry wrote on Fri, 10 June 2016 09:18When I purchased my coach in 2002, one of the many things that needed work were the two roof AC's. Both of the would run the fan, but neither would start and blow cold air. Someone mentioned the following modification which removes the time delay and allows the AC's to work.
http://www.gmcmhphotos.com/photos/g3615-roof-ac-modification.html
Someone receintly asked me if there was a down side to doing this modification. Is it ok running with out it? Anyone know?
Larry,
The only downside it that if they get blinked (either by the power supply or the operator), they will probably pop the breaker when trying to restart.
Matt I will expand on what Matt said. The time delay relay is there to keep the compressor from trying to start too soon after it goes off, so that it won't try to start against high head pressure. That strain to try to get spinning against the pressure would create a whole lotta current, and the breaker would trip. Say you are on shore power and the compressor is running. The power goes out momentarily, long enough for the compressor to stop. It comes back on, and the AC tries to resume where it left off, and the compressor can't budge. It trips the breaker. Let it sit long enough for the refrigerant to redistribute itself, and you are good to go. That time delay relay does that automagically.
Now that your eyes have glazed over in boredom, let me add that just because the AC doesn't cool doesn't mean the time delay relay is the problem. Another cause is low/no refrigerant. You can tell when the compressor comes on, and if it does, then the delay relay is not the problem. And remember that there are two fans. One for circulating air inside (the one you say comes on) and the one outside that blows over the condenser. That one might have mud-dauber nests locking it up. If no air blows over the condenser, you get no cooling.
These 40 year old roof ACs generally get replaced because someone wants a low profile one, or one that uses less current, or one that is quieter, and so on. Very rarely are they graveyard dead due to a failed compressor or low/no refrigerant. It usually turns out to be mud-daubers or corroded connectors or fan motor bearings need oil and even the time delay relay.
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| Re: Time delay on original roof AC's [message #301982 is a reply to message #301951] |
Fri, 10 June 2016 18:22 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The OEM Duotherms have one fan motor with 2 shafts. squirl cage on the inside evaporator and fan blade w slinger on the outside condenser.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Time delay on original roof AC's [message #302041 is a reply to message #301963] |
Sun, 12 June 2016 09:14 |
trapper
Messages: 52
Registered: April 2015
Location: Saskatchewan, Canada
Karma: 0
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Interesting info. I was one of the folks that posed the question. I came across Larry's very helpful documentation when looking for causes of my compressor not coming on. In my case it was definitely the relay causing the problem. Compressor would not ever kick in.
So if the power burps and the breaker is tripped...we are talking about inside the coach? Or coming from the shore power?
How does one get a replacement relay?
75 Glenbrook
[Updated on: Sun, 12 June 2016 09:15] Report message to a moderator |
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| Re: Time delay on original roof AC's [message #302049 is a reply to message #302041] |
Sun, 12 June 2016 11:36 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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Should be the breaker in the coach but very ikely the internal compressor overload will cycle a time or two and it will then start. If new ones aren't available some rv repair places have a pile of old units to get one from.
Roy Keen
Minden,NV
76 X Glenbrook
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