A/C MOV identification request

SteveG · 01-17-2008, 01:38 PM

With my recent heat pump episode I was told by RV Products that the Positive Temperature Coefficient Resistormetal NOT <STRIKE>a metal oxide varistors(MOV)</STRIKE> would be the first to go and their failure would be obvious. Since my heat pumps still seem to be working OK I thought I would take a look to see what the PTCR look like when they were healthy. I think I have identified them but would appreciate it if someone would please confirm. See photo below. Thanks.

SteveG · 01-17-2008, 01:38 PM

With my recent heat pump episode I was told by RV Products that the Positive Temperature Coefficient Resistormetal NOT <STRIKE>a metal oxide varistors(MOV)</STRIKE> would be the first to go and their failure would be obvious. Since my heat pumps still seem to be working OK I thought I would take a look to see what the PTCR look like when they were healthy. I think I have identified them but would appreciate it if someone would please confirm. See photo below. Thanks.

ChasA · 01-17-2008, 02:22 PM

Steve,
Every MOV I ever saw was much smaller than what I see in your picture, and they were not cylindrical, they were disk shaped with two wires coming out. In fact they looked just like ceramic disk capacitors, except they had the letters "MOV" printed on them. Mind you, I haven't kept up with electronics for quite a few years, and manufacturers may have changed the form factor. I suggest you look for any markings on the components and tell us what if any markings on them.
Chas

SteveG · 01-17-2008, 03:39 PM

ChasA, thanks for the reply. I mis-spoke when I named it a MOV. It is a Positive Temperature Coefficient Resistor. Just in case I guessed wrong I took a photo of the entire thing. Anything look like a PTCR?

TheRVGuy · 01-17-2008, 05:26 PM

Yep, far right hand side on top of the black capacitors. About 1 1/4 wide by 1 high about 1/4 thick, red wire on top.

They will be burned and toasted when damaged.

Hope this helps,

Mike

Izzyblueye · 01-18-2008, 03:31 AM

Thanks guys-- I copied to my file of basement air and heat pump folder. Now can you enlighten an electrically challenged individual as to what a PTCR is? Thanks again.

Clay L · 01-18-2008, 05:08 AM

The resistance increases as the temperature increases.
Of course this is true for most metals and many materials, so I am not sure what is special about this guy. Must have a specific temperature co-efficient and resistance.

codgerbill · 01-18-2008, 05:27 AM

Hmmmmmm

Being a former Electric Utility Employee........
MOV's are the newer type lightening arrestors. They replaced the porcelain ones that virtually exploded when hit by lightening. The newer MOV's just got sorta pregnant and oozed some gunk when hit by lightening. I am wonderning if there are in fact MOV's in the ac/Heat pump controls and do they serve the same type protection (IE: overvoltage protection)?

gunawo · 01-18-2008, 06:33 AM

It is an electronic switch in the compressor starting circuit. When the A/C is first started the PTCR is cold and has no resistance so it allows current to flow through the start capacitor to the start winding of the compressor giving it a start "kick", it immediately heats,resistance increases and cuts off current to the start capacitor as soon as the compressor is up to speed. The run capacitor then takes over and feeds a small amount of out of phase current to the start winding to assist the compressor in running efficiently

Izzyblueye · 01-18-2008, 07:26 AM

gunawo: Thank you sir: I will file this with the original picture. I have not found many techs that know a twit about these basement systems so far.

NeilV · 01-18-2008, 08:50 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Homer:
gunawo: Thank you sir: I will file this with the original picture. I have not found many techs that know a twit about these basement systems so far. </div></BLOCKQUOTE>

Homer,

The last time I bought them they were sold as a set with the capacitors. The parts guy went out back and confered with the tech and said since you replace them as a set they stock and sell them that way. It was less than $50 for two kits when I did mine this past labor day. The unit failed when we stopped for some groceries so we called ahead and had the kits waiting at the parts counter when we drove by the dealership. I put one set in before we left the parking lot and finished the job and got the second half of the system back in operation when we arrived at the campground.

SteveG · 01-18-2008, 04:18 PM

Per the RV Products technician the PRTCs are sold as "Start Kits". The kit number for my 2004 Journey basement air unit is 8333A-9021. I did not ask a price. But I am pretty sure he said they could be purchased at Camping World. He also said that they are easy to install but to be sure to discharge the capactors to prevent electrical shock.

Thanks for the help.

NeilV · 01-19-2008, 01:09 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by SteveG:
Per the RV Products technician the PRTCs are sold as "Start Kits". The kit number for my 2004 Journey basement air unit is 8333A-9021. I did not ask a price. But I am pretty sure he said they could be purchased at Camping World. He also said that they are easy to install but to be sure to discharge the capactors to prevent electrical shock.

Thanks for the help. </div></BLOCKQUOTE>

Steve,

They only take a few minutes to install and are normally stocked at the parts counter next door to Camping World in Sefner/Tampa at LazyDays. I was surprised that I got out of it so inexpensively replacing both capacitors and starters myself for less than $50.

One word of caution, the starters come apart easily so put them in right the first time and don't handle them too much. The disks are just slid up between the two contact plates with the connector tabs in the plastic housing snapping into place and if you mess with them they may slide apart on you. Once they have been in use for a while they may come apart quite easily if you try to unplug them or swap them for diagnostics.

If they come apart you may be able to snap them back together. You will have four parts a plastic housing, metal disk and two metal plates with connector tabs on them. Make sure everything is clean and then slide the metal plates back up into the slot in the bottom of the housing making sure that the tabs stick out where they belong. Then slide the disk back into place. Be carefull not to break the plastic as it may be brittle.

Get a spare if you have one come apart even if you are able to get it back together so you will not have to do without for an extended period if it does not stay together and fails again.

SteveG · 01-19-2008, 06:07 PM

Neil, thanks for the good information. I've copied it and tucked it away into my Air Condidioning file. Hopefully the A/C unit will keep on chugging.

Just to get things named correctly for those who may read this thread in the future I have re-marked the photo below showing the PTCRs.

Finhawk · 01-19-2008, 07:01 PM

Do these control the propane heat when the ambient temp drops to a certain point?

NeilV · 01-20-2008, 02:00 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Finhawk:
Do these control the propane heat when the ambient temp drops to a certain point? </div></BLOCKQUOTE>

No they don't, these are to provide starting current for the compressor motors in the AC/HeatPump system.

gunny · 01-20-2008, 04:08 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by gunawo:
It is an electronic switch in the compressor starting circuit. When the A/C is first started the PTCR is cold and has no resistance so it allows current to flow through the start capacitor to the start winding of the compressor giving it a start "kick", it immediately heats,resistance increases and cuts off current to the start capacitor as soon as the compressor is up to speed. The run capacitor then takes over and feeds a small amount of out of phase current to the start winding to assist the compressor in running efficiently </div></BLOCKQUOTE>

Explained that very well. Thank You.